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path: root/src/devices/cpu/alto2/a2disk.cpp
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// license:BSD-3-Clause
// copyright-holders:Juergen Buchmueller
/*****************************************************************************
 *
 *   Xerox AltoII disk interface
 *
 *****************************************************************************/
#include "alto2cpu.h"

#define GET_KADDR_SECTOR(kaddr)         X_RDBITS(kaddr,16, 0, 3)            //!< get sector number from address register
#define PUT_KADDR_SECTOR(kaddr,val)     X_WRBITS(kaddr,16, 0, 3,val)        //!< put sector number into address register
#define GET_KADDR_CYLINDER(kaddr)       X_RDBITS(kaddr,16, 4,12)            //!< get cylinder number from address register
#define PUT_KADDR_CYLINDER(kaddr,val)   X_WRBITS(kaddr,16, 4,12,val)        //!< put cylinder number int address register
#define GET_KADDR_HEAD(kaddr)           X_RDBITS(kaddr,16,13,13)            //!< get head number from address register
#define PUT_KADDR_HEAD(kaddr,val)       X_WRBITS(kaddr,16,13,13,val)        //!< put head number into address register
#define GET_KADDR_DRIVE(kaddr)          X_RDBITS(kaddr,16,14,14)            //!< get drive (unit) number from address register
#define PUT_KADDR_DRIVE(kaddr,val)      X_WRBITS(kaddr,16,14,14,val)        //!< put drive (unit) number into address register
#define GET_KADDR_RESTORE(kaddr)        X_RDBITS(kaddr,16,15,15)            //!< get restore flag from address register
#define PUT_KADDR_RESTORE(kaddr,val)    X_WRBITS(kaddr,16,15,15,val)        //!< putt restore flag into address register

#define GET_KADR_SEAL(kadr)             X_RDBITS(kadr,16, 0, 7)             //!< get command seal from command register
#define PUT_KADR_SEAL(kadr,val)         X_WRBITS(kadr,16, 0, 7,val)         //!< put command seal into command register
#define GET_KADR_HEADER(kadr)           X_RDBITS(kadr,16, 8, 9)             //!< get r/w/c for header from command register
#define PUT_KADR_HEADER(kadr,val)       X_WRBITS(kadr,16, 8, 9,val)         //!< put r/w/c for header from command register
#define GET_KADR_LABEL(kadr)            X_RDBITS(kadr,16,10,11)             //!< get r/w/c for label from command register
#define PUT_KADR_LABEL(kadr,val)        X_WRBITS(kadr,16,10,11,val)         //!< put r/w/c for label into command register
#define GET_KADR_DATA(kadr)             X_RDBITS(kadr,16,12,13)             //!< get r/w/c for data from command register
#define PUT_KADR_DATA(kadr,val)         X_WRBITS(kadr,16,12,13,val)         //!< put r/w/c for data into command register
#define GET_KADR_NOXFER(kadr)           X_RDBITS(kadr,16,14,14)             //!< get no transfer flag from command register
#define PUT_KADR_NOXFER(kadr,val)       X_WRBITS(kadr,16,14,14,val)         //!< put no transfer flag into command register
#define GET_KADR_UNUSED(kadr)           X_RDBITS(kadr,16,15,15)             //!< get unused (drive?) flag from command register
#define PUT_KADR_UNUSED(kadr,val)       X_WRBITS(kadr,16,15,15,val)         //!< put unused (drive?) flag into command register

#define GET_KSTAT_SECTOR(kstat)         X_RDBITS(kstat,16,0,3)              //!< get current sector number from status register
#define PUT_KSTAT_SECTOR(kstat,val)     X_WRBITS(kstat,16,0,3,val)          //!< put current sector number into status register
#define GET_KSTAT_DONE(kstat)           X_RDBITS(kstat,16,4,7)              //!< get 'done' field from status register (017)
#define PUT_KSTAT_DONE(kstat,val)       X_WRBITS(kstat,16,4,7,val)          //!< put 'done' field int status register (017)
#define GET_KSTAT_SEEKFAIL(kstat)       X_RDBITS(kstat,16,8,8)              //!< get seek fail flag from status register
#define PUT_KSTAT_SEEKFAIL(kstat,val)   X_WRBITS(kstat,16,8,8,val)          //!< put seek fail flag into status register
#define GET_KSTAT_SEEK(kstat)           X_RDBITS(kstat,16,9,9)              //!< get seek busy flag (strobe) from status register
#define PUT_KSTAT_SEEK(kstat,val)       X_WRBITS(kstat,16,9,9,val)          //!< put seek busy flag (strobe) into status register
#define GET_KSTAT_NOTRDY(kstat)         X_RDBITS(kstat,16,10,10)            //!< get drive not ready flag from status register
#define PUT_KSTAT_NOTRDY(kstat,val)     X_WRBITS(kstat,16,10,10,val)        //!< put drive not ready flag into status register
#define GET_KSTAT_DATALATE(kstat)       X_RDBITS(kstat,16,11,11)            //!< get data late flag from status register
#define PUT_KSTAT_DATALATE(kstat,val)   X_WRBITS(kstat,16,11,11,val)        //!< put data late flag into status register
#define GET_KSTAT_IDLE(kstat)           X_RDBITS(kstat,16,12,12)            //!< get idle flag from status register (idle is a software flag)
#define PUT_KSTAT_IDLE(kstat,val)       X_WRBITS(kstat,16,12,12,val)        //!< put idle flag into status register (idle is a software flag)
#define GET_KSTAT_CKSUM(kstat)          X_RDBITS(kstat,16,13,13)            //!< get checksum flag from status register (checksum is a software flag; it is ORed when 0)
#define PUT_KSTAT_CKSUM(kstat,val)      X_WRBITS(kstat,16,13,13,val)        //!< put checksum flag into status register (checksum is a software flag; it is ORed when 0)
#define GET_KSTAT_COMPLETION(kstat)     X_RDBITS(kstat,16,14,15)            //!< get completion code from status register (completion is a 2-bit software latch)
#define PUT_KSTAT_COMPLETION(kstat,val) X_WRBITS(kstat,16,14,15,val)        //!< put completion code into status register (completion is a 2-bit software latch)

#define GET_KCOM_XFEROFF(kcom)          X_RDBITS(kcom,16,1,1)               //!< get transfer off flag from controller command (hardware command register)
#define PUT_KCOM_XFEROFF(kcom,val)      X_WRBITS(kcom,16,1,1,val)           //!< put transfer off flag into controller command (hardware command register)
#define GET_KCOM_WDINHIB(kcom)          X_RDBITS(kcom,16,2,2)               //!< get word task inhibit flag from controller command (hardware command register)
#define PUT_KCOM_WDINHIB(kcom,val)      X_WRBITS(kcom,16,2,2,val)           //!< put word task inhibit flag into controller command (hardware command register)
#define GET_KCOM_BCLKSRC(kcom)          X_RDBITS(kcom,16,3,3)               //!< get bit clock source flag from controller command (hardware command register)
#define PUT_KCOM_BCLKSRC(kcom,val)      X_WRBITS(kcom,16,3,3,val)           //!< put bit clock source flag into controller command (hardware command register)
#define GET_KCOM_WFFO(kcom)             X_RDBITS(kcom,16,4,4)               //!< get write fixed frequency oscillator flag from controller command (hardware command register)
#define PUT_KCOM_WFFO(kcom,val)         X_WRBITS(kcom,16,4,4,val)           //!< put write fixed frequency oscillator flag into controller command (hardware command register)
#define GET_KCOM_SENDADR(kcom)          X_RDBITS(kcom,16,5,5)               //!< get send address flag from controller command (hardware command register)
#define PUT_KCOM_SENDADR(kcom,val)      X_WRBITS(kcom,16,5,5,val)           //!< put send address flag into controller command (hardware command register)

/** @brief completion codes (only for documentation, since this is microcode defined) */
enum {
	STATUS_COMPLETION_GOOD,
	STATUS_COMPLETION_HARDWARE_ERROR,
	STATUS_COMPLETION_CHECK_ERROR,
	STATUS_COMPLETION_ILLEGAL_SECTOR
};

/** @brief record numbers per sector in INCRECNO order */
enum {
	RECNO_HEADER,
	RECNO_NOTHING,
	RECNO_LABEL,
	RECNO_DATA
};


/** @brief read/write/check numbers */
enum {
	RWC_READ,
	RWC_CHECK,
	RWC_WRITE,
	RWC_WRITE2
};

#if ALTO2_DEBUG
/** @brief human readable names for the KADR<- modes */
static const char *rwc_name[4] = {"read", "check", "write", "write2"};
static const char* raise_lower[2] = {"/","\\"};
#endif

/**
 * <PRE>
 * SECTOR, ERROR WAKEUPS
 *
 *
 * Monoflop pulse duration:
 * tW = K * Rt * Cext * (1 + 0.7/Rt)
 * K = 0.28 for 74123
 * Rt = kOhms
 * Cext = pF
 *
 *                     +------+
 *  CLRSTAT' >---------oS'    | 15k, .47uF (=470000pF)
 *                     | MONO | 2066120ns ~= 2ms
 *                     | FLOP |
 *                     |      | Q'     +----+
 *  READY'   >---------oC'    o--------|NAND|    ERRWAKE'
 *                     +------+        |    o----+
 *  RDYLAT'  >-------------------------|    |    |
 *                                     +----+    |
 *                                               |
 *                                               |
 *                         .---------------------+
 *                         |
 *                     +---o--+ Q            +------+
 *               +-----|J  S' |----+---------|S     | 30k, .01uF (=10000pF)
 *               |     |      |    |         | MONO | 85960ns ~= 86us
 *   SECT[4] >---|-----|CLK   |    |         | FLOP |
 *               |     |   21a|    |         |      | Q'
 *               | 1 >-|K' C' |    |     1 >-|C'    |--------------------> SECLATE
 *               |     +---o--+    |         +------+
 *               |         |       |
 *               +---------+-------|-----------------------------------.
 *                                 |                                   |
 *                 +---------------+                                   |
 *                 |                                                   |
 *                 |       1                 1   RESET' >------+       |
 *                 |       |                 |                 |       |
 *                 |   +---o--+ Q        +---o--+ Q        +---o--+ Q  |
 *                 +---|J  S' |----------|J  S' |----------|J  S' |------> STSKENA
 *                     |      |          |      |          |      |    |
 *  SYSCLKB' >--+------|CLK   |  .-------|CLK   |  +-------|CLK   |    |
 *              |      |   21b|  |       |   22a|  |       |   22b| Q' |
 *              |  1 >-|K' C' |  |   1 >-|K' C' |  |   +---|K' C' |----+-> WAKEST'
 *              |      +---o--+  |       +---o--+  |   |   +---o--+    |
 *              |          |     |           |     |   |       1       |
 *              |          +-----|-----------+-----|---|---------------+
 *              |                |                 |   |
 *              +----------------+-----------------+   |
 *                                                     |
 *                                     +----+          |
 *   BLOCK   >-------------------------|NAND|          |
 *                                     |    o----------+
 *  STSKACT  >-------------------------|    |
 *                                     +----+
 *
 * A CLRSTAT starts the monoflop, and READY', i.e. the ready signal from the disk
 * drive, clears it. The Q' output is thus 0 for some time after CLRSTAT, and as
 * long as the disk signals being ready.
 *
 * If the disk is not ready, i.e. the Q' being 1, and if RDYLAT' - the READY' state
 * latched at the most recent CLRSTAT - is also 1, the ERRWAKE' signal will go 0.
 *
 * Each new sector (SECT[4]' going 1) will clock the FF 21a, which changes
 * its Q output depending on WAKEST' (K' is always 1):
 *   if J and K' are both 1, sets its Q to 1.
 *   if J is 0, and K' is 1, keeps Q as is.
 * So Q becomes 0 by WAKEST' going 0, and it becomes 1 with the next sector, if
 * WAKEST' is 1.
 *
 * The mono-flop to the right will generate a SECLATE signal, if WAKEST' was
 * not 0 when the disk signalled a new sector.
 *
 * The three J-K FFs at the bottom are all clocked with the rising edge of
 * SYSCLKB' (i.e falling edge of SYSCLKB).
 *
 * The left JK-FF propagates the current state of the upper JK-FF's Q output
 * to its own Q. The middle propagates the previous state of the left one,
 * and the JK-FF to the right delays the wandering Q for a third SYSCLKB'
 * rising edge, but only in one case:
 * 1)  if J and K' are both 1, set its Q to 1.
 * 2)  if J is 1, and K' is 0, toggle Q.
 * 3)  if J is 0, and K' is 1, keep Q as is.
 * 4)  if J and K' are both 0, set its Q to 0.
 *
 * The right FF's K' is 0 whenever the BLOCK signal (see DISK WORD TIMING)
 * and the sector task active signal (STSKACT) are 1 at the same time.
 *
 * Case 1) is the normal case, and it wakes the KSECT on the third SYSCLKB'
 * positive edge. It resets at that same time the left, middle, and upper
 * J-K FFs .
 *
 * Case 2) is due, when the sector task is already active the moment
 * the BLOCK signal arrives. This toggles the output, i.e. removes the
 * wake.
 *
 * Case 3) is for an active sector task without a new sector.
 *
 * And finally case 4) happens when an active sector task sees no new
 * sector, and BLOCK rises.
 *
 * (This is like the video timing's dwt_blocks and dht_blocks signals)
 * </PRE>
 */

/**
 * @brief monoflop 31a pulse duration
 * Rt = 15k, Cext = .47uF (=470000pF) => 2066120ns (~2ms)
 */
#define TW_READY    2066120

/**
 * @brief monoflop 31b pulse duration
 * Rt = 30k, Cext = .01uF (=10000pF) => 86960ns (~85us)
 *
 * There's something wrong with this, or the KSEC would never ever
 * be able to commence the KWD. The SECLATE monoflop ouput has to go
 * high some time into the KSEC task microcode, before the sequence
 * error state is checked.
 *
 *  TW_SECLATE  (85960 nsec)
 *  TW_SECLATE  (46*ALTO2_UCYCLE)
 *  TW_SECLATE  8596
 */
#define TW_SECLATE  8596

/** @brief monoflop 52b pulse duration
 * Rt = 20k, Cext = 0.01uF (=10000pF) => 57960ns (~58us)
 */
#define TW_STROBON  57960

/**
 * <PRE>
 * DISK WORD TIMING
 *
 *
 *                       SECLATE ----+  +-+-+-+---< 1
 *                                   |  | | | |
 *                                +--o-----------+ CARRY +---+
 *                                | CLR 1 2 4 8  |-------|INVo-----> WDDONE'
 *                +---+  BITCLK'  |              |       +---+
 *    BITCLK >----|INVo----+------|CLK/   74161  |
 *                +---+    |      +----o---------+
 *                         |           |LOAD'
 *              +----------+           |
 *              |  +----+              |
 *              +--|NAND|              |
 *                 |    o----+         |
 *  HIORDBIT >-----|    |    |         |
 *                 +----+    |         |
 *                           |         |
 *                       +---o--+ Q    |
 *    BUS[4] >--------+--|J  S' |------+
 *                    |  |      |                               +----+
 *    LDCOM' >--------|--|CLK   |                        +------|NAND|
 *                    |  |   67b|                        |      |    o----> WAKEWDT'
 *                    +--|K' C' |                        |   +--|    |
 *                       +---o--+                        |   |  +----+
 *                           |                           |   |
 *                           1                           |   +----------+
 *                                                       |              |
 * OK TO RUN >---------------+                 1         |       1      |
 * (1 in AltoI)              |                 |         |       |      |
 *                       +---o--+ Q        +---o--+ Q    |   +---o--+ Q |
 *                   1 >-|J  S' |----------|J  S' |------+---|J  S' |---+
 *                       |      |          |      |      |   |      |
 *   WDDONE' >-----------|CLK   |  +-------|CLK   |   .--|---|CLK   |
 *                       |   43b|  |       |   53a|   |  |   |   43a|
 *                   1 >-|K' C' |  | +-----|K' C' |   |  `---|K' C' o---+
 *                       +---o--+  | |     +---o--+   |      +---o--+ Q'|
 *                           |     | |         |      |          |      |
 *                           +-----|-|---------|------|----------|------+
 *                                 | |         |      |          |
 *  SYSCLKA' >---------------------|-|---------|------+          |
 *                                 | |         |                 |
 *  WDALLOW  >---------------------|-|---------+-----------------+
 *                                 | |         |
 *  SYSCLKB' >---------------------+ |     +---o--+ Q
 *                                 | | 0 >-|J  S' |-------------> WDINIT
 *                                 | |     |      |
 *              +----+             +-|-----|CLK   |
 *     BLOCK >--|NAND|               |     |   53b|
 *              |    o---------------+-----|K  C' |
 *  WDTSKACT >--|    |                     +---o--+
 *              +----+                         |
 *                                             1
 *
 *
 * If SECLATE is 0, WDDONE' never goes low (counter's clear has precedence).
 *
 * If SECLATE is 1, WDDONE', the counter will count:
 *
 * If HIORDBIT is 1 at the falling edge of BITCLK, it sets the J-K flip-flop 67b, and
 * thus takes away the LOAD' assertion from the counter. It has been loaded with
 * 15, so it counts to 16 on the next rising edge and makes WDDONE' go to 0.
 *
 * If HIORDBIT is 0 at the falling edge of BITCLK, counting continues as it was
 * preset with BUS[4] at the last KCOM<- load:
 *
 * If BUS[4] was 1, both J and K' of the FF (74109) will be 1 at the rising edge
 * of LDCOM' (at the end of KCOM<-) and Q will be 1 => LOAD' is deasserted.
 *
 * If BUS[4] was 0, both J and K' will be 0, and Q will be 0 => LOAD' asserted.
 *
 * WDDONE' going from 0 to 1 will make the Q output of FF 43b go to 1.
 * The FF is also set, as long as OK TO RUN is 0.
 *
 * The FF 53a is clocked with falling edge of SYSCLKB (rising of SYSCLKB'),
 * and will:
 *   if J and K' are both 1, set its Q to 1.
 *   if J is 1, and K' is 0, toggle Q.
 *   if J is 0, and K' is 1, keep Q as is.
 *   if J and K' are both 0, set its Q to 0.
 * J is = Q of the FF 43b.
 * K is = 0, if both BLOCK and WDTASKACT are 1, and 1 otherwise.
 *
 * The FF 43a is clocked with falling edge of SYSCLKA (rising of SYSCLKA').
 * Its J and K' inputs are the Q output of the previous (middle) FF, thus
 * it will propagate the middle FF's Q to its own Q when SYSCLKA goes 0.
 *
 * If Q (53a) and Q (43a) are both 1, the WAKEKWDT' is 0 and the
 * word task wakeup signal is sent.
 *
 * WDALLOW going 0 asynchronously resets the 53a and 43a FFs, and thus
 * deasserts the WAKEKWD'. It also asynchronously sets the FF 53b, and
 * its output Q is the WDINIT signal.
 *
 * WDINIT is also deasserted with SYSCLKB going high, whenever both BLOCK
 * and WDTSKACT are 1.
 *
 * Whoa there! :-)
 * </PRE>
 */
#define WDALLOW (!GET_KCOM_WDINHIB(m_dsk.kcom))
#define WDINIT  ((m_dsk.ff_53b & JKFF_Q) ? 1 : 0)
#define RDYLAT  ((m_dsk.ff_45a & JKFF_Q) ? 1 : 0)
#define SEQERR  ((m_task == task_ksec && m_dsk.seclate == 0) || (m_task == task_kwd && m_dsk.bitcount == 15))
#define ERRWAKE (RDYLAT | m_dsk.ready_mf31a)
#define SEEKOK  (m_dsk.seekok)

/**
 * @brief disk word timing
 *
 * Implement the FIFOs and gates in the description above.
 *
 * @param bitclk the current bitclk level
 * @param datin the level of the bit read from the disk
 * @param block contains the task number of a blocking task, or 0 otherwise
 */
void alto2_cpu_device::kwd_timing(int bitclk, int datin, int block)
{
	diablo_hd_device* dhd = m_drive[m_dsk.drive];
	int wddone = m_dsk.wddone;      // get previous state of word-done
	int i;
	uint8_t s0, s1;

	LOG((this,LOG_DISK,9,"   *** KWD timing bitclk:%d datin:%d block:%d\n", bitclk, datin, block));
	if (0 == m_dsk.seclate)
	{
		// if SECLATE is 0, WDDONE' never goes low (counter's clear has precedence).
		if (m_dsk.bitcount) {
			LOG((this,LOG_DISK,7,"   SECLATE:0 clears bitcount:0\n"));
			m_dsk.bitcount = 0;
		}
	}
	else
	{
		// SECLATE is 1
		if (m_dsk.bitclk && !bitclk)
		{
			// on the falling edge of bitclk the counter will count or be loaded
			if ((m_dsk.shiftin & (1 << 16)) && !GET_KCOM_WFFO(m_dsk.kcom)) {
				/*
				 * If HIORDBIT is 1 at the falling edge of BITCLK, it sets the
				 * JK-FF 67b, and thus takes away the LOAD' assertion from the
				 * counter. It has been loaded with 15, so it counts to 16 on
				 * the next rising edge and makes WDDONE' go to 0.
				 */
				LOG((this,LOG_DISK,7,"   HIORDBIT:1 sets WFFO:1\n"));
				PUT_KCOM_WFFO(m_dsk.kcom, 1);
				// TODO: show disk indicators
			}
			/*
			 * Falling edge of BITCLK, counting continues as it was preset
			 * with BUS[4] (WFFO) at the last KCOM<- load, or as set by a
			 * 1 bit being read in HIORDBIT.
			 */
			if (GET_KCOM_WFFO(m_dsk.kcom)) {
				/*
				 * If BUS[4] (WFFO) was 1, both J and K' of the FF (74109) will
				 * be 1 at the rising edge of LDCOM' (at the end of KCOM<-)
				 * and Q will be 1. LOAD' is deassterted: count on clock.
				 */
				m_dsk.bitcount = (m_dsk.bitcount + 1) % 16;
				LOG((this,LOG_DISK,6,"   WFFO:1 count bitcount:%2d\n", m_dsk.bitcount));
			} else {
				/*
				 * If BUS[4] (WFFO) was 0, both J and K' will be 0, and Q
				 * will be 0. LOAD' is asserted and will load on rising bitclock (now)
				 */
				m_dsk.bitcount = 15;
				LOG((this,LOG_DISK,6,"   WFFO:0 load bitcount:%2d\n", m_dsk.bitcount));
			}
		}
		if (!m_dsk.bitclk && bitclk) {
			// rising edge of bitclk
			m_dsk.shiftin = (m_dsk.shiftin << 1) | datin;       // clock the input shift register
			m_dsk.shiftout = m_dsk.shiftout << 1;               // and the output shift register too
		}
	}

	if (m_dsk.wddone != wddone) {
		LOG((this,LOG_DISK,8,"   WDDONE':%d->%d\n", m_dsk.wddone, wddone));
	}

	if (15 == m_dsk.bitcount) {
		/* CARRY = 1 -> WDDONE' = 0 */
		wddone = 0;
		if (m_dsk.wddone == 0) {
			/*
			 * Latch a new data word while WDDONE is 0
			 * Note: The shifter outputs for bits 0 to 14 are connected
			 * to the latches inputs 1 to 15, while input bit 0 comes
			 * from the current datin.
			 * Shifter output 15 is the HIORDBIT signal.
			 */
			m_dsk.datain = m_dsk.shiftin & 0177777;
			/* load the output shift register */
			m_dsk.shiftout = m_dsk.dataout;
			LOG((this,LOG_DISK,8,"   LATCH in:%06o (0x%04x) out:%06o (0x%04x)\n", m_dsk.datain, m_dsk.datain, m_dsk.dataout, m_dsk.dataout));
		}
	} else {
		/* CARRY = 0 -> WDDONE' = 1 */
		wddone = 1;
	}

	// remember previous state of word-done
	m_dsk.wddone = wddone;

	/**
	 * JK flip-flop 43b (word task)
	 * <PRE>
	 * CLK  WDDONE'
	 * J    1
	 * K'   1
	 * S'   1
	 * C'   WDTSKENA
	 * Q    to 53a J
	 * </PRE>
	 */
	s0 = m_dsk.ff_43b;
	s1 = wddone ? JKFF_CLK : JKFF_0;
	s1 |= JKFF_J;
	s1 |= JKFF_K;
	if (m_dsk.ok_to_run)
		s1 |= JKFF_S;
	if (!(m_dsk.ff_43a & JKFF_Q))
		s1 |= JKFF_C;
	m_dsk.ff_43b = update_jkff(s0, s1, "43b KWD   ");

	// loop over the 4 stages of sysclka and sysclkb transitions
	for (i = 0; i < 4; i++) {
#if ALTO2_DEBUG
		if (m_sysclka0[i] != m_sysclka1[i]) {
			LOG((this,LOG_DISK,9,"   SYSCLKA' %s\n", raise_lower[m_sysclka1[i]]));
		}
		if (m_sysclkb0[i] != m_sysclkb1[i]) {
			LOG((this,LOG_DISK,9,"   SYSCLKB' %s\n", raise_lower[m_sysclkb1[i]]));
		}
#endif

		/**
		 * JK flip-flop 53b (word task)
		 * <PRE>
		 * CLK  SYSCLKB'
		 * J    0
		 * K'   (BLOCK & WDTSKACT)'
		 * S'   WDALLOW
		 * C'   1
		 * Q    WDINIT
		 * </PRE>
		 */
		s0 = m_dsk.ff_53b;
		s1 = m_sysclkb1[i];
		if (block != task_kwd)
			s1 |= JKFF_K;           // (BLOCK & WDTSKACT)'
		if (WDALLOW)
			s1 |= JKFF_S;
		s1 |= JKFF_C;
		m_dsk.ff_53b = update_jkff(s0, s1, "53b KWD   ");

		/**
		 * JK flip-flop 53a (word task)
		 * <PRE>
		 * CLK  SYSCLKB'
		 * J    from 43b Q
		 * K'   (BLOCK & WDTSKACT)'
		 * S'   1
		 * C'   WDALLOW
		 * Q    to 43a J and K'
		 * </PRE>
		 */
		s0 = m_dsk.ff_53a;
		s1 = m_sysclkb1[i];
		if (m_dsk.ff_43b & JKFF_Q)
			s1 |= JKFF_J;
		if (block != task_kwd)
			s1 |= JKFF_K;
		s1 |= JKFF_S;
		if (WDALLOW)
			s1 |= JKFF_C;
		m_dsk.ff_53a = update_jkff(s0, s1, "53a KWD   ");

		/**
		 * JK flip-flop 43a (word task)
		 * <PRE>
		 * CLK  SYSCLKA'
		 * J    from 53a Q
		 * K'   from 53a Q
		 * S'   1
		 * C'   WDALLOW
		 * Q    WDTSKENA', Q' WDTSKENA
		 * </PRE>
		 */
		s0 = m_dsk.ff_43a;
		s1 = m_sysclka1[i];
		if (m_dsk.ff_53a & JKFF_Q)
			s1 |= JKFF_J;
		if (m_dsk.ff_53a & JKFF_Q)
			s1 |= JKFF_K;
		s1 |= JKFF_S;
		if (WDALLOW)
			s1 |= JKFF_C;
		m_dsk.ff_43a = update_jkff(s0, s1, "43a KWD   ");

		/**
		 * JK flip-flop 45a (ready latch)
		 * <PRE>
		 * CLK  SYSCLKA'
		 * J    READY' from drive
		 * K'   1
		 * S'   1
		 * C'   CLRSTAT'
		 * Q    RDYLAT'
		 * </PRE>
		 */
		s0 = m_dsk.ff_45a;
		s1 = m_sysclka1[i];
		if (dhd->get_ready_0())
			s1 |= JKFF_J;
		s1 |= JKFF_K;
		s1 |= JKFF_S;
		s1 |= JKFF_C;       // FIXME: CLRSTAT' ?
		m_dsk.ff_45a = update_jkff(s0, s1, "45a RDYLAT");

		/**
		 * sets the seqerr flip-flop 45b (Q' is SEQERR)
		 * JK flip-flop 45b (seqerr latch)
		 * <PRE>
		 * CLK  SYSCLKA'
		 * J    1
		 * K'   SEQERR'
		 * S'   CLRSTAT'
		 * C'   1
		 * Q    to KSTAT[11] DATALATE
		 * </PRE>
		 */
		s0 = m_dsk.ff_45b;
		s1 = m_sysclka1[i];
		s1 |= JKFF_J;
		if (SEQERR)
			s1 |= JKFF_K;
		s1 |= JKFF_S;       // FIXME: CLRSTAT' ?
		s1 |= JKFF_C;
		m_dsk.ff_45b = update_jkff(s0, s1, "45b SEQERR");

		/**
		 * JK flip-flop 22b (sector task)
		 * <PRE>
		 * CLK  SYSCLKB'
		 * J    from 22a Q
		 * K'   (BLOCK & STSKACT)'
		 * S'   1 (really it's RESET')
		 * C'   1
		 * Q    STSKENA; Q' WAKEKST'
		 * </PRE>
		 */
		s0 = m_dsk.ff_22b;
		s1 = m_sysclkb1[i];
		if (m_dsk.ff_22a & JKFF_Q)
			s1 |= JKFF_J;
		if (block != task_ksec)
			s1 |= JKFF_K;
		s1 |= JKFF_S;   // FIXME: RESET' ?
		s1 |= JKFF_C;
		m_dsk.ff_22b = update_jkff(s0, s1, "22b KSEC  ");

		/**
		 * JK flip-flop 22a (sector task)
		 * <PRE>
		 * CLK  SYSCLKB'
		 * J    from 21b Q
		 * K'   1
		 * S'   1
		 * C'   WAKEST'
		 * Q    to 22b J
		 * </PRE>
		 */
		s0 = m_dsk.ff_22a;
		s1 = m_sysclkb1[i];
		if (m_dsk.ff_21b & JKFF_Q)
			s1 |= JKFF_J;
		s1 |= JKFF_K;
		s1 |= JKFF_S;
		if (!(m_dsk.ff_22b & JKFF_Q))
			s1 |= JKFF_C;
		m_dsk.ff_22a = update_jkff(s0, s1, "22a KSEC  ");

		/**
		 * JK flip-flop 21b (sector task)
		 * <PRE>
		 * CLK  SYSCLKB'
		 * J    from 21a Q
		 * K'   1
		 * S'   1
		 * C'   WAKEST'
		 * Q    to 22a J
		 * </PRE>
		 */
		s0 = m_dsk.ff_21b;
		s1 = m_sysclkb1[i];
		if (m_dsk.ff_21a & JKFF_Q)
			s1 |= JKFF_J;
		s1 |= JKFF_K;
		s1 |= JKFF_S;
		if (!(m_dsk.ff_22b & JKFF_Q))
			s1 |= JKFF_C;
		m_dsk.ff_21b = update_jkff(s0, s1, "21b KSEC  ");
	}

	// The 53b FF Q output is the WDINIT signal.
	if (WDINIT != m_dsk.wdinit) {
		m_dsk.wdinit0 = m_dsk.wdinit;
		// rising edge immediately
		if ((m_dsk.wdinit = WDINIT) == 1)
			m_dsk.wdinit0 = 1;
		LOG((this,LOG_DISK,8,"   WDINIT:%d\n", m_dsk.wdinit));
	}

	/*
	 * If Q (53a) and Q (43a) are both 1, the WAKEKWDT'
	 * output is 0 and the disk word task wakeup signal is asserted.
	 */
	if ((m_dsk.ff_53a  & JKFF_Q) && (m_dsk.ff_43a & JKFF_Q)) {
		if (m_dsk.wdtskena == 1) {
			LOG((this,LOG_DISK,2,"   WDTSKENA':0 and WAKEKWDT':0 wake KWD\n"));
			m_dsk.wdtskena = 0;
			m_task_wakeup |= 1 << task_kwd;
		}
	} else if (m_dsk.ff_43a & JKFF_Q) {
		/*
		 * If Q (43a) is 1, the WDTSKENA' signal is deasserted.
		 */
		if (m_dsk.wdtskena == 0) {
			LOG((this,LOG_DISK,2,"   WDTSKENA':1\n"));
			m_dsk.wdtskena = 1;
			m_task_wakeup &= ~(1 << task_kwd);
		}
	}

	if (0 != m_dsk.kfer) {
		// no fatal error: ready AND not seqerr AND seekok
		if (!RDYLAT && !SEQERR && SEEKOK) {
			LOG((this,LOG_DISK,6,"   reset KFER\n"));
			m_dsk.kfer = 0;
		}
	} else {
		// fatal error: not ready OR seqerr OR not seekok
		if (RDYLAT) {
			LOG((this,LOG_DISK,6,"   RDYLAT sets KFER\n"));
			m_dsk.kfer = 1;
		}
		if (SEQERR) {
			LOG((this,LOG_DISK,6,"   SEQERR sets KFER\n"));
			m_dsk.kfer = 1;
		}
		if (!SEEKOK) {
			LOG((this,LOG_DISK,6,"   not SEEKOK sets KFER\n"));
			m_dsk.kfer = 1;
		}
	}

	/*
	 * The FF 22b Q output is the STSKENA (sector task enable)
	 * signal, the Q' is the WAKEKST' signal.
	 */
	if (m_dsk.ff_22b & JKFF_Q) {
		if (0 == (m_task_wakeup & (1 << task_ksec))) {
			LOG((this,LOG_DISK,6,"   STSKENA:1; WAKEST':0 wake KSEC\n"));
			m_task_wakeup |= 1 << task_ksec;
		}
	} else {
		if (0 != (m_task_wakeup & (1 << task_ksec))) {
			LOG((this,LOG_DISK,6,"   STSKENA:0; WAKEST':1\n"));
			m_task_wakeup &= ~(1 << task_ksec);
		}
	}

	/**
	 * JK flip-flop 21a (sector task)
	 * <PRE>
	 * CLK  SECT4 (inverted sector mark from drive)
	 * J    WAKEST'
	 * K'   1
	 * S'   ERRWAKE'
	 * C'   WAKEST'
	 * Q    to seclate monoflop
	 * </PRE>
	 */
	s0 = m_dsk.ff_21a;
	s1 = dhd->get_sector_mark_0() ? JKFF_CLK : JKFF_0;
	if (!(m_dsk.ff_22b & JKFF_Q))
		s1 |= JKFF_J;
	s1 |= JKFF_K;
	if (!ERRWAKE)
		s1 |= JKFF_S;
	if (!(m_dsk.ff_22b & JKFF_Q))
		s1 |= JKFF_C;
	m_dsk.ff_21a = update_jkff(s0, s1, "21a KSEC  ");

	// If the KSEC FF 21a Q goes 1, pulse the SECLATE signal for some time.
	if (!(m_dsk.ff_21a_old & JKFF_Q) && (m_dsk.ff_21a & JKFF_Q)) {
		m_dsk.seclate_timer->adjust(attotime::from_nsec(TW_SECLATE), 1);
		if (m_dsk.seclate) {
			m_dsk.seclate = 0;
			LOG((this,LOG_DISK,6,"   SECLATE -> 0 pulse until cycle %lld\n", cycle() + TW_SECLATE / ALTO2_UCYCLE));
		}
	}

	// check if write and erase gate, or read gate are changed
	if ((m_task_wakeup & (1 << task_ksec)) || GET_KCOM_XFEROFF(m_dsk.kcom) || m_dsk.kfer) {
#if ALTO2_DEBUG
		if (0 == m_dsk.egate || 0 == m_dsk.wrgate || 0 == m_dsk.rdgate) {
			// log the reason why gates are deasserted
			LOG((this,LOG_DISK,6,"   deassert gates because of"));
			if (m_task_wakeup & (1 << task_ksec)) {
				LOG((this,LOG_DISK,6," KSECWAKE"));
			}
			if (GET_KCOM_XFEROFF(m_dsk.kcom)) {
				LOG((this,LOG_DISK,6," XFEROFF"));
			}
			if (m_dsk.kfer) {
				LOG((this,LOG_DISK,6," KFER"));
			}
			LOG((this,LOG_DISK,6,"\n"));
		}
#endif
		// sector task is active OR xferoff is set OR fatal error
		dhd->set_egate(m_dsk.egate = 1);
		dhd->set_wrgate(m_dsk.wrgate = 1);
		dhd->set_rdgate(m_dsk.rdgate = 1);
	} else {
		if (m_dsk.krwc & RWC_WRITE) {
			if (m_dsk.ok_to_run) {
#if ALTO2_DEBUG
				if (1 == m_dsk.egate || 1 == m_dsk.wrgate) {
					LOG((this,LOG_DISK,6,"   assert "));
					if (m_dsk.egate) {
						LOG((this,LOG_DISK,6," EGATE"));
					}
					if (m_dsk.wrgate) {
						LOG((this,LOG_DISK,6," WRGATE"));
					}
					LOG((this,LOG_DISK,6,"\n"));
				}
#endif
				// assert erase and write gates
				dhd->set_egate(m_dsk.egate = 0);
				dhd->set_wrgate(m_dsk.wrgate = 0);
			}
		} else {
#if ALTO2_DEBUG
			if (1 == m_dsk.rdgate) {
				LOG((this,LOG_DISK,6,"   assert RDGATE\n"));
			}
#endif
			// assert read gate
			dhd->set_rdgate(m_dsk.rdgate = 0);
		}
	}

	m_dsk.ff_21a_old = m_dsk.ff_21a;
	m_dsk.bitclk = bitclk;
	m_dsk.datin = datin;
}


/**
 * @brief timer callback to take away the SECLATE pulse (monoflop)
 * @param ptr some unused pointer
 * @param arg contains the seclate value
 */
void alto2_cpu_device::disk_seclate(void* ptr, int32_t arg)
{
	(void)ptr;
	LOG((this,LOG_DISK,2,"   SECLATE -> %d\n", arg));
	m_dsk.seclate = arg;
	m_dsk.seclate_timer->enable(false);
}

/**
 * @brief timer callback to take away the OK TO RUN pulse (reset)
 * @param ptr some unused pointer
 * @param arg contains the ok_to_run value
 */
void alto2_cpu_device::disk_ok_to_run(void* ptr, int32_t arg)
{
	(void)ptr;
	LOG((this,LOG_DISK,2,"   OK TO RUN -> %d\n", arg));
	m_dsk.ok_to_run = arg;
	m_dsk.ok_to_run_timer->enable(false);
}

/**
 * @brief timer callback to pulse the STROBE' signal to the drive
 *
 * STROBE' pulses are sent to the drive at a rate that depends on
 * the monoflop 52b external resistor and capacitor.
 *
 * The drive compares the cylinder number that is presented on
 * its inputs against the current cylinder, and if they don't
 * match steps into the corresponding direction.
 *
 * On the falling edge of a strobe, the drive sets the log_addx_interlock
 * flag 0 (LAI, active low). On the rising edge of the strobe the drive then
 * indicates seek completion by setting addx_acknowledge to 0 (ADDRACK, active low).
 * If the seek is not yet complete, it instead keeps the seek_incomplete
 * flag 0 (SKINC, active low). If the seek would go beyond the last cylinder,
 * the drive deasserts seek_incomplete, but does not assert the addx_acknowledge.
 *
 * @param ptr some unused pointer
 * @param arg contains the drive, cylinder, and restore flag
 */
void alto2_cpu_device::disk_strobon(void* ptr, int32_t arg)
{
	(void)ptr;
	int unit = arg % 2;
	int restore = (arg / 2) % 2;
	int cylinder = arg / 4;

	diablo_hd_device* dhd = m_drive[unit];
	LOG((this,LOG_DISK,2,"   STROBE #%d restore:%d cylinder:%d dhd:%p\n", unit, restore, cylinder, dhd));

	dhd->set_cylinder(cylinder);
	dhd->set_restore(restore);
	// This is really monoflop 52a generating a very short 0 pulse
	for (int strobe = 0; strobe < 2; strobe++) {
		uint8_t s0, s1;
		dhd->set_strobe(strobe);    // pulse the strobe signal to the unit

		int lai = dhd->get_log_addx_interlock_0();
		LOG((this,LOG_DISK,6,"       LAI':%d\n", lai));
		/**
		 * JK flip-flop 44a (LAI' clocked)
		 * <PRE>
		 * CLK  LAI
		 * J    1
		 * K'   1
		 * S'   1
		 * C'   CLRSTAT' (not now)
		 * Q    to seekok
		 * </PRE>
		 */
		s0 = m_dsk.ff_44a;
		s1 = lai ? JKFF_CLK : JKFF_0;
		s1 |= JKFF_J;
		s1 |= JKFF_K;
		s1 |= JKFF_S;
		s1 |= JKFF_C;
		m_dsk.ff_44a = update_jkff(s0, s1, "44a LAI   ");
		if (dhd->get_addx_acknowledge_0() == 0 && (m_dsk.ff_44a & JKFF_Q)) {
			/* if address is acknowledged, and Q' of FF 44a, clear the strobe */
			m_dsk.strobe = 0;
		}
	}

	if (dhd->get_addx_acknowledge_0()) {
		/* no acknowledge yet */

	} else {
		/* clear the monoflop 52b, i.e. no timer restart */
		LOG((this,LOG_DISK,2,"       STROBON:%d\n", m_dsk.strobe));
		/* update the seekok status: SKINC' && LAI' && Q' of FF 44a */
		int seekok = dhd->get_seek_incomplete_0();
		if (seekok != m_dsk.seekok) {
			m_dsk.seekok = seekok;
			LOG((this,LOG_DISK,2,"       SEEKOK:%d\n", m_dsk.seekok));
		}
	}

	LOG((this,LOG_DISK,2,"   current cylinder:%d\n", dhd->get_cylinder()));

	/* if the strobe is still set, restart the timer */
	if (m_dsk.strobe) {
		m_dsk.strobon_timer->adjust(attotime::from_nsec(TW_STROBON), arg);
	} else {
		m_dsk.strobon_timer->reset();
	}
}

/** @brief timer callback to change the READY monoflop 31a */
void alto2_cpu_device::disk_ready_mf31a(void* ptr, int32_t arg)
{
	diablo_hd_device* dhd = m_drive[m_dsk.drive];
	m_dsk.ready_mf31a = arg & dhd->get_ready_0();
	/* log the not ready result with level 0, else 2 */
	LOG((this,LOG_DISK,m_dsk.ready_mf31a ? 0 : 2,"   mf31a:%d %sready\n", m_dsk.ready_mf31a, m_dsk.ready_mf31a ? "not " : ""));
}

/**
 * @brief called if one of the disk tasks (task_kwd or task_ksec) blocks
 *
 * @param task task that blocks (either task_ksec or task_kwd)
 */
void alto2_cpu_device::disk_block(int task)
{
	kwd_timing(m_dsk.bitclk, m_dsk.datin, task);
}

/**
 * @brief bs_read_kstat early: bus driven by disk status register KSTAT
 * <PRE>
 * Part of the KSTAT register is made of two 4 bit latches S8T10 (Signetics).
 * The signals BUS[8-11] are the current state of:
 *     BUS[0-3]   SECT[0-3]; from the Winchester drive (inverted)
 *     BUS[8]     SEEKOK'
 *     BUS[9]     SRWRDY' from the Winchester drive
 *     BUS[10]    RDYLAT' (latched READY' at last CLRSTAT, FF 45a output Q)
 *     BUS[11]    SEQERR (latched SEQERR at last CLRSTAT, FF 45b output Q')
 * The signals BUS[12,14-15] are just as they were loaded at KSTAT<- time.
 *     BUS[13]    CHSEMERROR (FF 44b output Q' inverted)
 * </PRE>
 */
void alto2_cpu_device::bs_early_read_kstat()
{
	diablo_hd_device* dhd = m_drive[m_dsk.drive];
	uint16_t r;

	/* KSTAT[4-7] bus is open */
	PUT_KSTAT_DONE(m_dsk.kstat, 017);

	/* KSTAT[8] latch the inverted seekok status */
	PUT_KSTAT_SEEKFAIL(m_dsk.kstat, m_dsk.seekok ? 0 : 1);

	/* KSTAT[9] latch the drive seek/read/write status */
	PUT_KSTAT_SEEK(m_dsk.kstat, dhd->get_seek_read_write_0());

	/* KSTAT[10] latch the latched (FF 45a at CLRSTAT) ready status (Q) */
	PUT_KSTAT_NOTRDY(m_dsk.kstat, m_dsk.ff_45a & JKFF_Q ? 1 : 0);

	/* KSTAT[11] latch the latched (FF 45b at CLRSTAT) seqerr status (Q') */
	PUT_KSTAT_DATALATE(m_dsk.kstat, m_dsk.ff_45b & JKFF_Q ? 0 : 1);

	/* KSTAT[13] latch the latched (FF 44b at CLRSTAT/KSTAT<-) checksum status */
	PUT_KSTAT_CKSUM(m_dsk.kstat, m_dsk.ff_44b & JKFF_Q ? 1 : 0);

	r = m_dsk.kstat;

	LOG((this,LOG_DISK,1,"   <-KSTAT; BUS &= %#o\n", r));
	LOG((this,LOG_DISK,2,"       SECTOR     : %#o\n", GET_KSTAT_SECTOR(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       DONE       : %#o\n", GET_KSTAT_DONE(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       SEEKFAIL   : %d\n", GET_KSTAT_SEEKFAIL(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       SEEK       : %d\n", GET_KSTAT_SEEK(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       NOTRDY     : %d\n", GET_KSTAT_NOTRDY(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       DATALATE   : %d\n", GET_KSTAT_DATALATE(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       IDLE       : %d\n", GET_KSTAT_IDLE(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       CKSUM      : %d\n", GET_KSTAT_CKSUM(m_dsk.kstat)));
	LOG((this,LOG_DISK,2,"       COMPLETION : %#o\n", GET_KSTAT_COMPLETION(m_dsk.kstat)));

	m_bus &= r;
}

/**
 * @brief bs_read_kdata early: bus driven by disk data register KDATA input
 *
 * The input data register is a latch that latches the contents of
 * the lower 15 bits of a 16 bit shift register in its more significant
 * 15 bits, and the current read data bit is the least significant
 * bit. This is handled in kwd_timing.
 */
void alto2_cpu_device::bs_early_read_kdata()
{
	uint16_t r;
	/* get the current word from the drive */
	r = m_dsk.datain;
	LOG((this,LOG_DISK,1,"   <-KDATA (%#o)\n", r));
	m_bus &= r;
}

/**
 * @brief f1_strobe late: initiates a disk seek
 *
 * Initiates a disk seek operation. The KDATA register must have
 * been loaded previously, and the SENDADR bit of the KCOM
 * register previously set to 1.
 */
void alto2_cpu_device::f1_late_strobe()
{
	if (GET_KCOM_SENDADR(m_dsk.kcom)) {
		LOG((this,LOG_DISK,1,"   STROBE (SENDADR:1)\n"));
		/* Set the STROBON flag and start the STROBON monoflop */
		m_dsk.strobe = 1;
		disk_strobon(nullptr,
			4 * GET_KADDR_CYLINDER(m_dsk.kaddr) +
			2 * GET_KADDR_RESTORE(m_dsk.kaddr) +
			m_dsk.drive);
	} else {
		LOG((this,LOG_DISK,1,"   STROBE (w/o SENDADR)\n"));
		/* FIXME: what to do if SENDADR isn't set? */
	}
}

/**
 * @brief f1_load_kstat late: load disk status register
 *
 * KSTAT[12-15] are loaded from BUS[12-15], except that BUS[13] is
 * ORed into KSTAT[13].
 *
 * NB: The 4 bits are just software, not changed by hardware
 */
void alto2_cpu_device::f1_late_load_kstat()
{
	LOG((this,LOG_DISK,1,"   KSTAT<-; BUS[12-15] %#o\n", m_bus));
	LOG((this,LOG_DISK,2,"       IDLE       : %d\n", GET_KSTAT_IDLE(m_bus)));
	LOG((this,LOG_DISK,2,"       CKSUM      : %d\n", GET_KSTAT_CKSUM(m_bus)));
	LOG((this,LOG_DISK,2,"       COMPLETION : %#o\n", GET_KSTAT_COMPLETION(m_bus)));

	/* KSTAT[12] is just taken from BUS[12] */
	PUT_KSTAT_IDLE(m_dsk.kstat, GET_KSTAT_IDLE(m_bus));

	/* KSTAT[14-15] are just taken from BUS[14-15] */
	PUT_KSTAT_COMPLETION(m_dsk.kstat, GET_KSTAT_COMPLETION(m_bus));

	/* May set the CKSUM flip-flop 44b
	 * JK flip-flop 44b (KSTAT<- clocked)
	 * CLK  SYSCLKA'
	 * J    !BUS[13]
	 * K'   1
	 * S'   1
	 * C'   CLRSTAT' (not now)
	 * Q    Q' inverted to BUS[13] on <-KSTAT
	 */
	for (int i = 0; i < 2; i++) {
		uint8_t s0, s1;
		s0 = m_dsk.ff_44b;
		s1 = i ? JKFF_CLK : JKFF_0;
		if (!GET_KSTAT_CKSUM(m_bus))
			s1 |= JKFF_J;
		s1 |= JKFF_K;
		s1 |= JKFF_S;
		s1 |= JKFF_C;
		m_dsk.ff_44b = update_jkff(s0, s1, "44b CKSUM ");
	}
}

/**
 * @brief f1_load_kdata late: load data out register, or the disk address register
 *
 * KDATA is loaded from BUS.
 */
void alto2_cpu_device::f1_late_load_kdata()
{
	m_dsk.dataout = m_bus;
	if (GET_KCOM_SENDADR(m_dsk.kcom)) {
		PUT_KADDR_SECTOR(m_dsk.kaddr, GET_KADDR_SECTOR(m_bus));
		PUT_KADDR_CYLINDER(m_dsk.kaddr, GET_KADDR_CYLINDER(m_bus));
		PUT_KADDR_HEAD(m_dsk.kaddr, GET_KADDR_HEAD(m_bus));
		PUT_KADDR_DRIVE(m_dsk.kaddr, GET_KADDR_DRIVE(m_bus));
		PUT_KADDR_RESTORE(m_dsk.kaddr, GET_KADDR_RESTORE(m_bus));
		PUT_KADDR_DRIVE(m_dsk.kaddr, GET_KADDR_DRIVE(m_bus));
		m_dsk.drive = GET_KADDR_DRIVE(m_dsk.kaddr);

		LOG((this,LOG_DISK,1,"   KDATA<-; BUS (%#o) (drive:%d restore:%d %d/%d/%02d)\n",
			m_bus,
			GET_KADDR_DRIVE(m_dsk.kaddr),
			GET_KADDR_RESTORE(m_dsk.kaddr),
			GET_KADDR_CYLINDER(m_dsk.kaddr),
			GET_KADDR_HEAD(m_dsk.kaddr),
			GET_KADDR_SECTOR(m_dsk.kaddr)));
#if 0
		/* printing changes in the disk address */
		{
			static int last_kaddr;
			if (m_dsk.kaddr != last_kaddr) {
				int c = GET_KADDR_CYLINDER(m_dsk.kaddr);
				int h = GET_KADDR_HEAD(m_dsk.kaddr);
				int s = GET_KADDR_SECTOR(m_dsk.kaddr);
				int page = DRIVE_PAGE(c,h,s);
				last_kaddr = m_dsk.kaddr;
				printf("    unit:%d restore:%d %d/%d/%02d page:%d\n",
					GET_KADDR_DRIVE(m_dsk.kaddr),
					GET_KADDR_RESTORE(m_dsk.kaddr),
					c, h, s, page);
			}
		}
#endif
	} else {
		LOG((this,LOG_DISK,1,"   KDATA<-; BUS %#o (%#x)\n", m_bus, m_bus));
	}
}

/**
 * @brief f1_increcno late: advances shift registers holding KADR
 *
 * Advances the shift registers holding the KADR register so that they
 * present the number and read/write/check status of the next record
 * to the hardware.
 *
 * <PRE>
 * Sheet 10, shifter (74195) parts #36 and #37
 *
 * Vcc, BUS[08], BUS[10], BUS[12] go to #36 A,B,C,D
 * Vcc, BUS[09], BUS[11], BUS[13] go to #37 A,B,C,D
 * A is connected to ground on both chips;
 * both shifters are loaded with KADR<-
 *
 * The QA outputs are #36 -> RECNO(0) and #37 -> RECNO(1)
 *
 * RECNO(0) (QA of #37) goes to J and K' of #36
 * RECNO(1) (QA of #36) is inverted and goes to J and K' of #37
 *
 *  shift/   RECNO(0)    RECNO(1)     R/W/C presented
 *   load      #37         #36        to the drive
 * ---------------------------------------------------
 *   load       0           0         HEADER
 * 1st shift    1           0         LABEL
 * 2nd shift    1           1         DATA
 * 3rd shift    0           1         (none) 0 = read
 * [ 4th        0           0         (none) 2 = write ]
 * [ 5th        1           0         (none) 3 = write ]
 * [ 6th        1           1         (none) 1 = check ]
 * </PRE>
 */
void alto2_cpu_device::f1_late_increcno()
{
	switch (m_dsk.krecno) {
	case RECNO_HEADER:
		m_dsk.krecno = RECNO_LABEL;
		m_dsk.krwc = GET_KADR_LABEL(m_dsk.kadr);
		LOG((this,LOG_DISK,2,"   INCRECNO; HEADER -> LABEL (%o, rwc:%o)\n", m_dsk.krecno, m_dsk.krwc));
		break;
	case RECNO_NOTHING:
		m_dsk.krecno = RECNO_HEADER;
		m_dsk.krwc = GET_KADR_HEADER(m_dsk.kadr);
		LOG((this,LOG_DISK,2,"   INCRECNO; NOTHING -> HEADER (%o, rwc:%o)\n", m_dsk.krecno, m_dsk.krwc));
		break;
	case RECNO_LABEL:
		m_dsk.krecno = RECNO_DATA;
		m_dsk.krwc = GET_KADR_DATA(m_dsk.kadr);
		LOG((this,LOG_DISK,2,"   INCRECNO; LABEL -> DATA (%o, rwc:%o)\n", m_dsk.krecno, m_dsk.krwc));
		break;
	case RECNO_DATA:
		m_dsk.krecno = RECNO_NOTHING;
		m_dsk.krwc = 0; /* read (?) */
		LOG((this,LOG_DISK,2,"   INCRECNO; DATA -> NOTHING (%o, rwc:%o)\n", m_dsk.krecno, m_dsk.krwc));
		break;
	}
	// TODO: show disk indicator
}

/**
 * @brief f1_clrstat late: reset all error latches
 *
 * Causes all error latches in the disk controller hardware to reset,
 * clears KSTAT[13].
 *
 * NB: IDLE (KSTAT[12]) and COMPLETION (KSTAT[14-15]) are not cleared
 */
void alto2_cpu_device::f1_late_clrstat()
{
	diablo_hd_device* dhd = m_drive[m_dsk.drive];
	uint8_t s0, s1;

	/* clears the LAI clocked flip-flop 44a
	 * JK flip-flop 44a (LAI' clocked)
	 * CLK  (LAI')'
	 * J    1
	 * K'   1
	 * S'   1
	 * C'   CLRSTAT'
	 * Q    to seekok
	 */
	s0 = m_dsk.ff_44a;
	s1 = m_dsk.ff_44a & JKFF_CLK;
	s1 |= JKFF_J;
	s1 |= JKFF_K;
	s1 |= JKFF_S;
	s1 &= ~JKFF_C;
	m_dsk.ff_44a = update_jkff(s0, s1, "44a LAI   ");

	/* clears the CKSUM flip-flop 44b
	 * JK flip-flop 44b (KSTAT<- clocked)
	 * CLK  SYSCLKA' (not used here, just clearing)
	 * J    1 (BUS[13] during KSTAT<-)
	 * K'   1
	 * S'   1
	 * C'   CLRSTAT'
	 * Q    to seekok
	 */
	s0 = m_dsk.ff_44b;
	s1 = m_dsk.ff_44b & JKFF_CLK;
	s1 |= m_dsk.ff_44b & JKFF_J;
	s1 |= JKFF_K;
	s1 |= JKFF_S;
	s1 &= ~JKFF_C;
	m_dsk.ff_44b = update_jkff(s0, s1, "44b CKSUM ");

	/* clears the rdylat flip-flop 45a
	 * JK flip-flop 45a (ready latch)
	 * CLK  SYSCLKA'
	 * J    READY' from drive
	 * K'   1
	 * S'   1
	 * C'   CLRSTAT'
	 * Q    RDYLAT'
	 */
	s0 = m_dsk.ff_45a;
	s1 = m_dsk.ff_45a & JKFF_CLK;
	if (dhd->get_ready_0())
		s1 |= JKFF_J;
	s1 |= JKFF_K;
	s1 |= JKFF_S;
	s1 &= ~JKFF_C;
	m_dsk.ff_45a = update_jkff(s0, s1, "45a RDYLAT");

	/* sets the seqerr flip-flop 45b (Q' is SEQERR)
	 * JK flip-flop 45b (seqerr latch)
	 * CLK  SYSCLKA'
	 * J    1
	 * K'   SEQERR'
	 * S'   CLRSTAT'
	 * C'   1
	 * Q    to KSTAT[11] DATALATE
	 */
	s0 = m_dsk.ff_45b;
	s1 = m_dsk.ff_45b & JKFF_CLK;
	s1 |= JKFF_J;
	if (!SEQERR)
		s1 |= JKFF_K;
	s1 &= ~JKFF_S;
	s1 |= JKFF_C;
	m_dsk.ff_45b = update_jkff(s0, s1, "45b SEQERR");

	/* set or reset monoflop 31a, depending on drive READY' */
	m_dsk.ready_mf31a = dhd->get_ready_0();

	/* start monoflop 31a, which resets ready_mf31a */
	m_dsk.ready_timer->adjust(attotime::from_nsec(TW_READY), 1);

	LOG((this,LOG_DISK,1,"   CLRSTAT (44a:%d 44b:%d 45a:%d 45b:%d 31a:%d)\n",
			m_dsk.ff_44a & JKFF_Q ? 1 : 0, m_dsk.ff_44b & JKFF_Q ? 1 : 0,
			m_dsk.ff_45a & JKFF_Q ? 1 : 0, m_dsk.ff_45b & JKFF_Q ? 1 : 0,
			m_dsk.ready_mf31a));
}

/**
 * @brief f1_load_kcom late: load the KCOM register from bus
 * <PRE>
 * This causes the KCOM register to be loaded from BUS[1-5]. The
 * KCOM register has the following interpretation:
 *  (1) XFEROFF = 1 inhibits data transmission to/from the m_dsk.
 *  (2) WDINHIB = 1 prevents the disk word task from awakening.
 *  (3) BCLKSRC = 0 takes bit clock from disk input or crystal clock, as appropriate.
 *      BCLKSRC = 1 force use of crystal clock.
 *  (4) WFFO = 0 holds the disk bit counter at -1 until a 1 bit is read.
 *      WFFO = 1 allows the bit counter to proceed normally.
 *  (5) SENDADR = 1 causes KDATA[4-12] and KDATA[15] to be signalled to disk unit as track address.
 *      SENDADR = 0 inhibits such signalling.
 * </PRE>
 */
void alto2_cpu_device::f1_late_load_kcom()
{
	uint16_t change = m_dsk.kcom ^ m_bus;
	m_dsk.kcom = m_bus;
	LOG((this,LOG_DISK,2,"   KCOM<-; BUS %06o\n", m_dsk.kcom));
	LOG((this,LOG_DISK,2,"       XFEROFF    : %d\n", GET_KCOM_XFEROFF(m_dsk.kcom)));
	LOG((this,LOG_DISK,2,"       WDINHIB    : %d\n", GET_KCOM_WDINHIB(m_dsk.kcom)));
	LOG((this,LOG_DISK,2,"       BCLKSRC    : %d\n", GET_KCOM_BCLKSRC(m_dsk.kcom)));
	LOG((this,LOG_DISK,2,"       WFFO       : %d\n", GET_KCOM_WFFO(m_dsk.kcom)));
	LOG((this,LOG_DISK,2,"       SENDADR    : %d\n", GET_KCOM_SENDADR(m_dsk.kcom)));
	if (GET_KCOM_WDINHIB(change)) {
		// WDALLOW going 0: should asynchronously reset 43a and 53a and set 53b
		if (m_task == task_kwd) {
			uint8_t s0, s1;
			/**
			 * JK flip-flop 53b (word task)
			 * <PRE>
			 * CLK  SYSCLKB'
			 * J    0
			 * K'   (BLOCK & WDTSKACT)'
			 * S'   WDALLOW
			 * C'   1
			 * Q    WDINIT
			 * </PRE>
			 */
			s0 = m_dsk.ff_53b;
			s1 = JKFF_0;
			if (WDALLOW)
				s1 |= JKFF_S;
			s1 |= JKFF_C;
			m_dsk.ff_53b = update_jkff(s0, s1, "53b KWD   ");

			/**
			 * JK flip-flop 53a (word task)
			 * <PRE>
			 * CLK  SYSCLKB'
			 * J    from 43b Q
			 * K'   (BLOCK & WDTSKACT)'
			 * S'   1
			 * C'   WDALLOW
			 * Q    to 43a J and K'
			 * </PRE>
			 */
			s0 = m_dsk.ff_53a;
			s1 = JKFF_0;
			if (m_dsk.ff_43b & JKFF_Q)
				s1 |= JKFF_J;
			s1 |= JKFF_S;
			if (WDALLOW)
				s1 |= JKFF_C;
			m_dsk.ff_53a = update_jkff(s0, s1, "53a KWD   ");

			/**
			 * JK flip-flop 43a (word task)
			 * <PRE>
			 * CLK  SYSCLKA'
			 * J    from 53a Q
			 * K'   from 53a Q
			 * S'   1
			 * C'   WDALLOW
			 * Q    WDTSKENA', Q' WDTSKENA
			 * </PRE>
			 */
			s0 = m_dsk.ff_43a;
			s1 = JKFF_0;
			if (m_dsk.ff_53a & JKFF_Q)
				s1 |= JKFF_J;
			if (m_dsk.ff_53a & JKFF_Q)
				s1 |= JKFF_K;
			s1 |= JKFF_S;
			if (WDALLOW)
				s1 |= JKFF_C;
			m_dsk.ff_43a = update_jkff(s0, s1, "43a KWD   ");
		}
	}
	// TODO: show disk indicator in the GUI?
}

/**
 * @brief f1_load_kadr late: load the KADR register from bus
 *
 * The KADR register is loaded from BUS[8-14]. This register has the format
 * of word C in section 6.0 above. In addition, it causes the head address
 * bit to be loaded from KDATA[13].
 *
 * NB: the record numer RECNO(0) and RECNO(1) is reset to 0
 */
void alto2_cpu_device::f1_late_load_kadr()
{
	/* store into the separate fields of KADR */
	PUT_KADR_SEAL(m_dsk.kadr, GET_KADR_SEAL(m_bus));
	PUT_KADR_HEADER(m_dsk.kadr, GET_KADR_HEADER(m_bus));
	PUT_KADR_LABEL(m_dsk.kadr, GET_KADR_LABEL(m_bus));
	PUT_KADR_DATA(m_dsk.kadr, GET_KADR_DATA(m_bus));
	PUT_KADR_NOXFER(m_dsk.kadr, GET_KADR_NOXFER(m_bus));
	PUT_KADR_UNUSED(m_dsk.kadr, GET_KADR_UNUSED(m_bus));

	int unit = GET_KADDR_DRIVE(m_dsk.kaddr);    // get selected drive from DATA[14] output (FF 67a really)
	int head = GET_KADDR_HEAD(m_dsk.dataout);   // latch head from DATA[13]
	PUT_KADDR_HEAD(m_dsk.kaddr, head);          // store in KADDR

	// select drive unit
	diablo_hd_device* dhd = m_drive[unit];
	dhd->select(unit);
	// set selected head
	dhd->set_head(head);

	// On KDAR<- load bit 0 of parts #36 and #37 is reset to 0, i.e. recno = 0
	m_dsk.krecno = 0;
	// current read/write/check is that for the header
	m_dsk.krwc = GET_KADR_HEADER(m_dsk.kadr);

	LOG((this,LOG_DISK,1,"   KADR<-; BUS[8-14] #%o\n", m_dsk.kadr));
	LOG((this,LOG_DISK,2,"       SEAL       : %d\n", GET_KADR_SEAL(m_dsk.kadr)));
	LOG((this,LOG_DISK,2,"       HEADER     : %s (%#o)\n",  rwc_name[GET_KADR_HEADER(m_dsk.kadr)], GET_KADR_HEADER(m_dsk.kadr)));
	LOG((this,LOG_DISK,2,"       LABEL      : %s (%#o)\n",  rwc_name[GET_KADR_LABEL(m_dsk.kadr)], GET_KADR_LABEL(m_dsk.kadr)));
	LOG((this,LOG_DISK,2,"       DATA       : %s (%#o)\n",  rwc_name[GET_KADR_DATA(m_dsk.kadr)], GET_KADR_DATA(m_dsk.kadr)));
	LOG((this,LOG_DISK,2,"       NOXFER     : %d\n",  GET_KADR_NOXFER(m_dsk.kadr)));
	LOG((this,LOG_DISK,2,"       unused     : %d (drive?)\n",  GET_KADR_UNUSED(m_dsk.kadr)));
	// TODO: show disk indicator in the GUI?
}

/**
 * @brief branch on disk word task active and init
 *
 * NEXT <- NEXT OR (WDTASKACT && WDINIT ? 037 : 0)
 */
void alto2_cpu_device::f2_late_init()
{
	// INIT = current task == KWD and WDINIT
	uint16_t r = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;
	LOG((this,LOG_DISK,1,"   INIT; %sbranch (%#o | %#o)\n", r ? "" : "no ", m_next2, r));
	m_next2 |= r;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief branch on read/write/check state of the current record
 * <PRE>
 * NEXT <- NEXT OR (current record to be written ? 3 : current record to be checked ? 2 : 0);
 *
 * NB: note how krecno counts 0,2,3,1 ... etc.
 * on 0: it presents the RWC for HEADER
 * on 2: it presents the RWC for LABEL
 * on 3: it presents the RWC for DATA
 * on 1: it presents the RWC 0, i.e. READ
 *
 * -NEXT[08] = -CHECK = RWC[0] | RWC[1]
 * -NEXT[09] = W/R = RWC[0]
 *
 *  rwc   | -next
 * -------+------
 *  0  0  |  0
 *  0  1  |  2
 *  1  0  |  3
 *  1  1  |  3
 * </PRE>
 */
void alto2_cpu_device::f2_late_rwc()
{
	uint16_t r;
	uint16_t init = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;

	switch (m_dsk.krwc & 3) {
	case 0:     // read
		r = 0;
		break;
	case 1:     // check
		r = 2;
		break;
	default:    // write
		r = 3;
	}

	switch (m_dsk.krecno) {
	case RECNO_HEADER:
		LOG((this,LOG_DISK,1,"   RWC; %sbranch header(%d):%s (%#o|%#o|%#o)\n",
			(r | init) ? "" : "no ", m_dsk.krecno,
			rwc_name[m_dsk.krwc], m_next2, r, init));
		break;
	case RECNO_NOTHING:
		LOG((this,LOG_DISK,1,"   RWC; %sbranch pageno(%d):%s (%#o|%#o|%#o)\n",
			(r | init) ? "" : "no ", m_dsk.krecno,
			rwc_name[m_dsk.krwc], m_next2, r, init));
		break;
	case RECNO_LABEL:
		LOG((this,LOG_DISK,1,"   RWC; %sbranch label(%d):%s (%#o|%#o|%#o)\n",
			(r | init) ? "" : "no ", m_dsk.krecno,
			rwc_name[m_dsk.krwc], m_next2, r, init));
		break;
	case RECNO_DATA:
		LOG((this,LOG_DISK,1,"   RWC; %sbranch data(%d):%s (%#o|%#o|%#o)\n",
			(r | init) ? "" : "no ", m_dsk.krecno,
			rwc_name[m_dsk.krwc], m_next2, r, init));
		break;
	}
	m_next2 |= r | init;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief f2_recno late: branch on the current record number by a lookup table
 * <PRE>
 * NEXT <- NEXT OR MAP (current record number) where
 *   MAP(0) = 0     (header)
 *   MAP(1) = 2     (label)
 *   MAP(2) = 3     (pageno)
 *   MAP(3) = 1     (data)
 * </PRE>
 * NB: The map isn't needed, because m_dsk.krecno counts exactly this way.
 */
void alto2_cpu_device::f2_late_recno()
{
	uint16_t r = m_dsk.krecno;
	uint16_t init = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;
	LOG((this,LOG_DISK,1,"   RECNO; %sbranch recno:%d (%#o|%#o|%#o)\n", (r | init) ? "" : "no ", m_dsk.krecno, m_next2, r, init));
	m_next2 |= r | init;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief branch on the data transfer state
 *
 * NEXT <- NEXT OR (if current command wants data transfer ? 1 : 0)
 */
void alto2_cpu_device::f2_late_xfrdat()
{
	uint16_t r = GET_KADR_NOXFER(m_dsk.kadr) ? 0 : 1;
	uint16_t init = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;
	LOG((this,LOG_DISK,1,"   XFRDAT; %sbranch (%#o|%#o|%#o)\n", (r | init) ? "" : "no ", m_next2, r, init));
	m_next2 |= r | init;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief branch on the disk ready signal
 *
 * NEXT <- NEXT OR (if disk not ready to accept command ? 1 : 0)
 */
void alto2_cpu_device::f2_late_swrnrdy()
{
	diablo_hd_device* dhd = m_drive[m_dsk.drive];
	uint16_t r = dhd->get_seek_read_write_0();
	uint16_t init = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;

	LOG((this,LOG_DISK,1,"   SWRNRDY; %sbranch (%#o|%#o|%#o)\n", (r | init) ? "" : "no ", m_next2, r, init));
	m_next2 |= r | init;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief branch on the disk fatal error condition
 *
 * NEXT <- NEXT OR (if fatal error in latches ? 0 : 1)
 */
void alto2_cpu_device::f2_late_nfer()
{
	uint16_t r = m_dsk.kfer ? 0 : 1;
	uint16_t init = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;

	LOG((this,LOG_DISK,1,"   NFER; %sbranch (%#o|%#o|%#o)\n", (r | init) ? "" : "no ", m_next2, r, init));
	m_next2 |= r | init;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief f2_strobon late: branch on the seek busy status
 *
 * NEXT <- NEXT OR (if seek strobe still on ? 1 : 0)
 * <PRE>
 * The STROBE signal is elongated with the help of two monoflops.
 * The first one has a rather short pulse duration:
 *  tW = K * Rt * Cext * (1 + 0.7/Rt)
 *  K = 0.28 for 74123
 *  Rt = kOhms
 *  Cext = pF
 * Rt = 20k, Cext = 150pf => 870ns
 *
 * The first one triggers the second, which will be cleared
 * by ADDRACK' from the drive going 0.
 * Its duration is:
 * Rt = 20k, Cext = 0.01uF (=10000pF) => 57960ns (~= 58us)
 * </PRE>
 */
void alto2_cpu_device::f2_late_strobon()
{
	uint16_t r = m_dsk.strobe;
	uint16_t init = (m_task == task_kwd && m_dsk.wdinit0) ? 037 : 0;

	LOG((this,LOG_DISK,2,"   STROBON; %sbranch (%#o|%#o|%#o)\n", (r | init) ? "" : "no ", m_next2, r, init));
	m_next2 |= r | init;
	m_dsk.wdinit0 = 0;
}

/**
 * @brief update the disk controller with a new bitclk
 *
 * @param id timer id
 * @param arg bit number
 */
void alto2_cpu_device::disk_bitclk(void* ptr, int32_t arg)
{
	(void)ptr;
	diablo_hd_device* dhd = m_drive[m_dsk.drive];
	int clk = arg & 1;
	int bit;

	/**
	 * The source for BITCLK and DATAIN depends on disk controller part #65
	 * <PRE>
	 *  BCLKSRC  W/R | BITCLK | DATAIN
	 * --------------+--------+---------
	 *    0       0  |  RDCLK | RDDATA
	 *    0       1  |  CLK/2 | DATOUT
	 *    1       0  |  CLK/2 | RDDATA
	 *    1       1  |  CLK/2 | DATOUT
	 * </PRE>
	 */
	if (m_dsk.krwc & RWC_WRITE) {
		if (GET_KCOM_XFEROFF(m_dsk.kcom)) {
			/* do anything, if the transfer is off? */
			kwd_timing(clk, 1, 0);
		} else {
			bit = (m_dsk.shiftout >> 15) & 1;
			kwd_timing(clk, bit, 0);
			LOG((this,LOG_DISK,8,"   BITCLK#%d bit:%d (write) @%lldns\n", arg, bit, ntime()));
			if (clk)
				dhd->wr_data(arg, bit);
			else
				dhd->wr_data(arg, 1);
		}
	} else if (GET_KCOM_BCLKSRC(m_dsk.kcom)) {
		/* always select the crystal clock */
		bit = dhd->rd_data(arg);
		LOG((this,LOG_DISK,8,"   BITCLK#%d bit:%d (read, crystal) @%lldns\n", arg, bit, ntime()));
		kwd_timing(clk, bit, 0);
	} else {
		/* if XFEROFF is set, keep the bit at 1 (RDGATE' is high) */
		if (GET_KCOM_XFEROFF(m_dsk.kcom)) {
			bit = 1;
		} else {
			clk = dhd->rd_clock(arg);
			bit = dhd->rd_data(arg);
			LOG((this,LOG_DISK,8,"   BITCLK#%d bit:%d (read, driveclk) @%lldns\n", arg, bit, ntime()));
		}
		kwd_timing(clk, bit, 0);
	}

	if (++arg < dhd->bits_per_sector()) {
		m_bitclk_time += m_dsk.bitclk_time[m_dsk.drive];
		m_bitclk_index = arg;
	} else {
		// stop the bitclock timer
		m_bitclk_time = -1;
	}
}

/**
 * @brief callback is called by the drive timer whenever a new sector starts
 *
 * @param unit the unit number
 */
void alto2_cpu_device::next_sector(int unit)
{
	diablo_hd_device* dhd = m_drive[unit];
	LOG((this,LOG_DISK,0,"%s dhd=%p\n", __FUNCTION__, dhd));
	// get bit time in attoseconds
	m_dsk.bitclk_time[unit] = dhd->bit_time().as_attoseconds();
	if (m_bitclk_time >= 0) {
		LOG((this,LOG_DISK,0,"   unit #%d stop bitclk\n", unit));
		m_bitclk_time = -1;
		m_bitclk_index = -1;
	}

	/* KSTAT[0-3] update the current sector in the kstat field */
	PUT_KSTAT_SECTOR(m_dsk.kstat, dhd->get_sector());

	/* clear input and output shift registers (?) */
	m_dsk.shiftin = 0;
	m_dsk.shiftout = 0;

	LOG((this,LOG_DISK,1,"   unit #%d sector %d start\n", unit, GET_KSTAT_SECTOR(m_dsk.kstat)));

	// TODO: verify current sector == requested sector and only then run the bitclk?
	// HACK: no command, no bit clock
	if (debug_read_mem(0521))
	{
		// Make the CPU execution loop call disk_bitclk
		m_bitclk_time = 0;
		m_bitclk_index = 0;
	}
}

/**
 * @brief initialize the disk context and insert a disk wort timer
 *
 * @result returns 0 on success, fatal() on error
 */
void alto2_cpu_device::init_disk()
{
	memset(&m_dsk, 0, sizeof(m_dsk));
	save_item(NAME(m_dsk.drive));
	save_item(NAME(m_dsk.kaddr));
	save_item(NAME(m_dsk.kadr));
	save_item(NAME(m_dsk.kstat));
	save_item(NAME(m_dsk.kcom));
	save_item(NAME(m_dsk.krecno));
	save_item(NAME(m_dsk.shiftin));
	save_item(NAME(m_dsk.shiftout));
	save_item(NAME(m_dsk.datain));
	save_item(NAME(m_dsk.dataout));
	save_item(NAME(m_dsk.krwc));
	save_item(NAME(m_dsk.kfer));
	save_item(NAME(m_dsk.wdtskena));
	save_item(NAME(m_dsk.wdinit0));
	save_item(NAME(m_dsk.wdinit));
	save_item(NAME(m_dsk.strobe));
	save_item(NAME(m_dsk.bitclk));
	save_item(NAME(m_dsk.datin));
	save_item(NAME(m_dsk.bitcount));
	save_item(NAME(m_dsk.carry));
	save_item(NAME(m_dsk.seclate));
	save_item(NAME(m_dsk.seekok));
	save_item(NAME(m_dsk.ok_to_run));
	save_item(NAME(m_dsk.ready_mf31a));
	save_item(NAME(m_dsk.seclate_mf31b));
#if 0
	save_item(NAME(m_dsk.ff_21a));
	save_item(NAME(m_dsk.ff_21a_old));
	save_item(NAME(m_dsk.ff_21b));
	save_item(NAME(m_dsk.ff_22a));
	save_item(NAME(m_dsk.ff_22b));
	save_item(NAME(m_dsk.ff_43b));
	save_item(NAME(m_dsk.ff_53a));
	save_item(NAME(m_dsk.ff_43a));
	save_item(NAME(m_dsk.ff_53b));
	save_item(NAME(m_dsk.ff_44a));
	save_item(NAME(m_dsk.ff_44b));
	save_item(NAME(m_dsk.ff_45a));
	save_item(NAME(m_dsk.ff_45b));
#endif

	/** @brief simulate previous sysclka */
	m_sysclka0[0] = JKFF_CLK;
	m_sysclka0[1] = JKFF_0;
	m_sysclka0[2] = JKFF_0;
	m_sysclka0[3] = JKFF_CLK;

	/** @brief simulate current sysclka */
	m_sysclka1[0] = JKFF_0;
	m_sysclka1[1] = JKFF_0;
	m_sysclka1[2] = JKFF_CLK;
	m_sysclka1[3] = JKFF_CLK;

	/** @brief simulate previous sysclkb */
	m_sysclkb0[0] = JKFF_CLK;
	m_sysclkb0[1] = JKFF_CLK;
	m_sysclkb0[2] = JKFF_0;
	m_sysclkb0[3] = JKFF_0;

	/** @brief simulate current sysclkb */
	m_sysclkb1[0] = JKFF_CLK;
	m_sysclkb1[1] = JKFF_0;
	m_sysclkb1[2] = JKFF_0;
	m_sysclkb1[3] = JKFF_CLK;

	m_dsk.wdtskena = 1;
	m_dsk.egate = 1;
	m_dsk.wrgate = 1;
	m_dsk.rdgate = 1;

	m_dsk.seclate = 0;
	m_dsk.ok_to_run = 0;

	m_dsk.kcom = 066000;

	m_dsk.strobon_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(alto2_cpu_device::disk_strobon),this));
	m_dsk.strobon_timer->reset();

	m_dsk.seclate_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(alto2_cpu_device::disk_seclate),this));
	m_dsk.seclate_timer->reset();

	m_dsk.ok_to_run_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(alto2_cpu_device::disk_ok_to_run),this));
	m_dsk.ok_to_run_timer->adjust(attotime::from_nsec(35 * ALTO2_UCYCLE / 1000), 1);

	m_dsk.ready_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(alto2_cpu_device::disk_ready_mf31a),this));
	m_dsk.ready_timer->reset();

	m_dsk.bitclk_time[0] = static_cast<int>(attotime::from_nsec(300).as_attoseconds() / 1000000);
	m_dsk.bitclk_time[1] = static_cast<int>(attotime::from_nsec(300).as_attoseconds() / 1000000);
}

/**
 * @brief exit disk controller - free all timers?
 */
void alto2_cpu_device::exit_disk()
{
	// nothing to do yet
}

void alto2_cpu_device::reset_disk()
{
	m_dsk.drive = 0;
	m_dsk.kaddr = 0;
	m_dsk.kadr = 0;
	m_dsk.kstat = 0;
	m_dsk.kcom = 066000;
	m_dsk.krecno = 0;
	m_dsk.egate = 1;
	m_dsk.wrgate = 1;
	m_dsk.rdgate = 1;
	m_dsk.shiftin = 0;
	m_dsk.shiftout = 0;
	m_dsk.datain = 0;
	m_dsk.dataout = 0;
	m_dsk.krwc = 0;
	m_dsk.kfer = 0;
	m_dsk.wdtskena = 1;
	m_dsk.wddone = 0;
	m_dsk.wdinit0 = 0;
	m_dsk.wdinit = 0;
	m_dsk.strobe = 0;
	m_dsk.strobon_timer->reset();
	m_dsk.bitclk = 0;
	m_dsk.bitclk_time[0] = attotime::from_nsec(300).as_attoseconds();
	m_dsk.bitclk_time[1] = attotime::from_nsec(300).as_attoseconds();
	m_dsk.datin = 0;
	m_dsk.bitcount = 0;
	m_dsk.seclate = 0;
	m_dsk.seclate_timer->reset();
	m_dsk.seekok = 0;
	m_dsk.ok_to_run = 0;
	m_dsk.ok_to_run_timer->adjust(attotime::from_nsec(35 * ALTO2_UCYCLE / 1000), 1);
	m_dsk.ready_mf31a = 0;
	m_dsk.ready_timer->reset();
	m_dsk.seclate_mf31b = 0;
	m_dsk.ff_21a = JKFF_0;
	m_dsk.ff_21a_old = JKFF_0;
	m_dsk.ff_21b = JKFF_0;
	m_dsk.ff_22a = JKFF_0;
	m_dsk.ff_22b = JKFF_0;
	m_dsk.ff_43b = JKFF_0;
	m_dsk.ff_53a = JKFF_0;
	m_dsk.ff_43a = JKFF_0;
	m_dsk.ff_53b = JKFF_0;
	m_dsk.ff_44a = JKFF_0;
	m_dsk.ff_44b = JKFF_0;
	m_dsk.ff_45a = JKFF_0;
	m_dsk.ff_45b = JKFF_0;
}