// license:BSD-3-Clause
// copyright-holders:Nathan Woods
/***************************************************************************
6883sam.cpp
Motorola 6883 Synchronous Address Multiplexer
The Motorola 6883 SAM has 16 bits worth of state, but the state is changed
by writing into a 32 byte address space; odd bytes set bits and even bytes
clear bits. Here is the layout:
31 Set TY Map Type 0: RAM/ROM 1: All RAM
30 Clear TY Map Type
29 Set M1 Memory Size 00: 4K 10: 64K Dynamic
28 Clear M1 Memory Size 01: 16K 11: 64K Static
27 Set M0 Memory Size
26 Clear M0 Memory Size
25 Set R1 MPU Rate 00: Slow 10: Fast
24 Clear R1 MPU Rate 01: Dual 11: Fast
23 Set R0 MPU Rate
22 Clear R0 MPU Rate
21 Set P1 Page #1 0: Low 1: High
20 Clear P1 Page #1
19 Set F6 Display Offset
18 Clear F6 Display Offset
17 Set F5 Display Offset
16 Clear F5 Display Offset
15 Set F4 Display Offset
14 Clear F4 Display Offset
13 Set F3 Display Offset
12 Clear F3 Display Offset
11 Set F2 Display Offset
10 Clear F2 Display Offset
9 Set F1 Display Offset
8 Clear F1 Display Offset
7 Set F0 Display Offset
6 Clear F0 Display Offset
5 Set V2 VDG Mode
4 Clear V2 VDG Mode
3 Set V1 VDG Mode
2 Clear V1 VDG Mode
1 Set V0 VDG Mode
0 Clear V0 VDG Mode
All parts of the SAM are fully emulated except R1/R0 (the changes in the
MPU rate are approximated) and M1/M0
***************************************************************************/
#include "emu.h"
#include "machine/6883sam.h"
//**************************************************************************
// CONSTANTS
//**************************************************************************
#define LOG_SAM 0
DEFINE_DEVICE_TYPE(SAM6883, sam6883_device, "sam6883", "MC6883 SAM")
//**************************************************************************
// DEVICE SETUP
//**************************************************************************
//-------------------------------------------------
// ctor
//-------------------------------------------------
sam6883_device::sam6883_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
: device_t(mconfig, SAM6883, tag, owner, clock)
, sam6883_friend_device_interface(mconfig, *this, 4)
, m_cpu_tag(nullptr)
, m_cpu_space_ref(AS_PROGRAM)
, m_cpu_space(nullptr)
, m_read_res(*this)
, m_space_0000(*this)
, m_space_8000(*this)
, m_space_A000(*this)
, m_space_C000(*this)
, m_space_FF00(*this)
, m_space_FF20(*this)
, m_space_FF40(*this)
, m_space_FF60(*this)
, m_space_FFE0(*this)
{
}
sam6883_friend_device_interface::sam6883_friend_device_interface(const machine_config &mconfig, device_t &device, int divider)
: device_interface(device, "sam6883")
, m_cpu(nullptr)
, m_sam_state(0x0000)
, m_divider(divider)
{
}
//-------------------------------------------------
// device_start - device-specific startup
//-------------------------------------------------
void sam6883_device::device_start()
{
// find the CPU
m_cpu = machine().device<cpu_device>(m_cpu_tag);
m_cpu_space = &m_cpu->space(m_cpu_space_ref);
// resolve callbacks
m_read_res.resolve_safe(0);
// install SAM handlers
m_cpu_space->install_read_handler(0xFFC0, 0xFFDF, read8_delegate(FUNC(sam6883_device::read), this));
m_cpu_space->install_write_handler(0xFFC0, 0xFFDF, write8_delegate(FUNC(sam6883_device::write), this));
// save state support
save_item(NAME(m_sam_state));
save_item(NAME(m_counter));
save_item(NAME(m_counter_xdiv));
save_item(NAME(m_counter_ydiv));
}
//-------------------------------------------------
// configure_bank - bank configuration
//-------------------------------------------------
void sam6883_device::configure_bank(int bank, uint8_t *memory, uint32_t memory_size, bool is_read_only)
{
configure_bank(bank, memory, memory_size, is_read_only, read8_delegate(), write8_delegate());
}
//-------------------------------------------------
// configure_bank - bank configuration
//-------------------------------------------------
void sam6883_device::configure_bank(int bank, read8_delegate rhandler, write8_delegate whandler)
{
configure_bank(bank, nullptr, 0, false, rhandler, whandler);
}
//-------------------------------------------------
// configure_bank - bank configuration
//-------------------------------------------------
void sam6883_device::configure_bank(int bank, uint8_t *memory, uint32_t memory_size, bool is_read_only, read8_delegate rhandler, write8_delegate whandler)
{
assert((bank >= 0) && (bank < ARRAY_LENGTH(m_banks)));
m_banks[bank].m_memory = memory;
m_banks[bank].m_memory_size = memory_size;
m_banks[bank].m_memory_read_only = is_read_only;
m_banks[bank].m_rhandler = rhandler;
m_banks[bank].m_whandler = whandler;
/* if we're configuring a bank that never changes, update it now */
switch(bank)
{
case 4:
m_space_FF00.point(m_banks[4], 0x0000);
break;
case 5:
m_space_FF20.point(m_banks[5], 0x0000);
break;
case 6:
m_space_FF40.point(m_banks[6], 0x0000);
break;
case 7:
m_space_FF60.point(m_banks[7], 0x0000);
break;
case 2:
m_space_FFE0.point(m_banks[2], 0x1FE0);
break;
}
}
//-------------------------------------------------
// device_reset - device-specific reset
//-------------------------------------------------
void sam6883_device::device_reset()
{
m_counter = 0;
m_counter_xdiv = 0;
m_counter_ydiv = 0;
m_sam_state = 0x0000;
update_state();
}
//-------------------------------------------------
// device_post_load - device-specific post load
//-------------------------------------------------
void sam6883_device::device_post_load()
{
device_t::device_post_load();
update_state();
}
//-------------------------------------------------
// update_state
//-------------------------------------------------
void sam6883_device::update_state(void)
{
update_memory();
update_cpu_clock();
}
//-------------------------------------------------
// update_memory
//-------------------------------------------------
void sam6883_device::update_memory(void)
{
// Memory size - allowed restricting memory accesses to something less than
// 32k
//
// This was a SAM switch that occupied 4 addresses:
//
// $FFDD (set) R1
// $FFDC (clear) R1
// $FFDB (set) R0
// $FFDA (clear) R0
//
// R1:R0 formed the following states:
// 00 - 4k
// 01 - 16k
// 10 - 64k
// 11 - static RAM (??)
//
// If something less than 64k was set, the low RAM would be smaller and
// mirror the other parts of the RAM
//
// TODO: Find out what "static RAM" is
// TODO: This should affect _all_ memory accesses, not just video ram
// TODO: Verify that the CoCo 3 ignored this
// switch depending on the M1/M0 variables
bool setup_rom = true;
switch(m_sam_state & (SAM_STATE_M1|SAM_STATE_M0))
{
case 0:
// 4K mode
m_space_0000.point(m_banks[0], 0x0000, m_banks[0].m_memory_size);
m_counter_mask = 0x0FFF;
break;
case SAM_STATE_M0:
// 16K mode
m_space_0000.point(m_banks[0], 0x0000, m_banks[0].m_memory_size);
m_counter_mask = 0x3FFF;
break;
case SAM_STATE_M1:
case SAM_STATE_M1|SAM_STATE_M0:
// 64k mode
if (m_sam_state & SAM_STATE_TY)
{
// full 64k RAM
m_space_0000.point(m_banks[0], 0x0000, m_banks[0].m_memory_size);
m_space_8000.point(m_banks[0], 0x8000);
m_space_A000.point(m_banks[0], 0xA000);
m_space_C000.point(m_banks[0], 0xC000);
m_counter_mask = 0xFFFF;
setup_rom = false;
}
else
{
// ROM/RAM
uint16_t ram_base = (m_sam_state & SAM_STATE_P1) ? 0x8000 : 0x0000;
m_space_0000.point(m_banks[0], ram_base, m_banks[0].m_memory_size);
m_counter_mask = 0x7FFF;
}
break;
}
if (setup_rom)
{
m_space_8000.point(m_banks[1], m_banks[1].m_memory_offset);
m_space_A000.point(m_banks[2], m_banks[2].m_memory_offset);
m_space_C000.point(m_banks[3], m_banks[3].m_memory_offset);
}
// update $FFE0-$FFFF
m_space_FFE0.point(m_banks[2], m_banks[2].m_memory_offset + 0x1FE0);
}
//-------------------------------------------------
// update_cpu_clock - adjusts the speed of the CPU
// clock
//-------------------------------------------------
void sam6883_friend_device_interface::update_cpu_clock(void)
{
// The infamous speed up poke.
//
// This was a SAM switch that occupied 4 addresses:
//
// $FFD9 (set) R1
// $FFD8 (clear) R1
// $FFD7 (set) R0
// $FFD6 (clear) R0
//
// R1:R0 formed the following states:
// 00 - slow 0.89 MHz
// 01 - dual speed ???
// 1x - fast 1.78 MHz
//
// R1 controlled whether the video addressing was speeded up and R0
// did the same for the CPU. On pre-CoCo 3 machines, setting R1 caused
// the screen to display garbage because the M6847 could not display
// fast enough.
//
// TODO: Make the overclock more accurate. In dual speed, ROM was a fast
// access but RAM was not. I don't know how to simulate this.
int speed = (m_sam_state & (SAM_STATE_R1|SAM_STATE_R0)) / SAM_STATE_R0;
m_cpu->owner()->set_unscaled_clock(device().clock() / (m_divider * (speed ? 2 : 4)));
}
//-------------------------------------------------
// set_bank_offset
//-------------------------------------------------
void sam6883_device::set_bank_offset(int bank, offs_t offset)
{
if (m_banks[bank].m_memory_offset != offset)
{
m_banks[bank].m_memory_offset = offset;
update_memory();
}
}
//-------------------------------------------------
// read
//-------------------------------------------------
READ8_MEMBER( sam6883_device::read )
{
return 0;
}
//-------------------------------------------------
// write
//-------------------------------------------------
WRITE8_MEMBER( sam6883_device::write )
{
/* alter the SAM state */
uint16_t xorval = alter_sam_state(offset);
/* based on the mask, apply effects */
if (xorval & (SAM_STATE_TY|SAM_STATE_M1|SAM_STATE_M0|SAM_STATE_P1))
update_memory();
if (xorval & (SAM_STATE_R1|SAM_STATE_R0))
update_cpu_clock();
}
//-------------------------------------------------
// horizontal_sync
//-------------------------------------------------
void sam6883_device::horizontal_sync(void)
{
bool carry;
// When horizontal sync occurs, bits B1-B3 or B1-B4 may be cleared (except in DMA mode). The catch
// is that the SAM's counter is a chain of flip-flops. Clearing the counter can cause carries to
// occur just as they can when the counter is bumped.
//
// This is critical in getting certain semigraphics modes to work correctly. Guardian uses this
// mode (see bug #1153). Special thanks to Ciaran Anscomb and Phill Harvey-Smith for figuring this
// out
switch((m_sam_state & (SAM_STATE_V2|SAM_STATE_V1|SAM_STATE_V0)) / SAM_STATE_V0)
{
case 0x01:
case 0x03:
case 0x05:
/* these SAM modes clear bits B1-B3 */
carry = (m_counter & 0x0008) ? true : false;
m_counter &= ~0x000F;
if (carry)
counter_carry_bit3();
break;
case 0x00:
case 0x02:
case 0x04:
case 0x06:
/* clear bits B1-B4 */
carry = (m_counter & 0x0010) ? true : false;
m_counter &= ~0x001F;
if (carry)
counter_carry_bit4();
break;
case 0x07:
/* DMA mode - do nothing */
break;
default:
fatalerror("Should not get here\n");
}
}
//-------------------------------------------------
// hs_w
//-------------------------------------------------
WRITE_LINE_MEMBER( sam6883_device::hs_w )
{
if (state)
{
horizontal_sync();
}
}
//-------------------------------------------------
// sam_space::ctor
//-------------------------------------------------
template<uint16_t _addrstart, uint16_t _addrend>
sam6883_device::sam_space<_addrstart, _addrend>::sam_space(sam6883_device &owner)
: m_owner(owner)
{
m_read_bank = nullptr;
m_write_bank = nullptr;
m_length = 0;
}
//-------------------------------------------------
// sam_space::cpu_space
//-------------------------------------------------
template<uint16_t _addrstart, uint16_t _addrend>
address_space &sam6883_device::sam_space<_addrstart, _addrend>::cpu_space() const
{
assert(m_owner.m_cpu_space != nullptr);
return *m_owner.m_cpu_space;
}
//-------------------------------------------------
// sam_space::point
//-------------------------------------------------
template<uint16_t _addrstart, uint16_t _addrend>
void sam6883_device::sam_space<_addrstart, _addrend>::point(const sam_bank &bank, uint16_t offset, uint32_t length)
{
if (LOG_SAM)
{
m_owner.logerror("sam6883_device::sam_space::point(): addrstart=0x%04X addrend=0x%04X offset=0x%04X length=0x%04X bank->m_memory=0x%p bank->m_memory_read_only=%s\n",
(unsigned) _addrstart,
(unsigned) _addrend,
(unsigned) offset,
(unsigned)length,
bank.m_memory,
bank.m_memory_read_only ? "true" : "false");
}
point_specific_bank(bank, offset, length, m_read_bank, _addrstart, _addrend, false);
point_specific_bank(bank, offset, length, m_write_bank, _addrstart, _addrend, true);
}
//-------------------------------------------------
// sam_space::point_specific_bank
//-------------------------------------------------
template<uint16_t _addrstart, uint16_t _addrend>
void sam6883_device::sam_space<_addrstart, _addrend>::point_specific_bank(const sam_bank &bank, uint32_t offset, uint32_t length, memory_bank *&memory_bank, uint32_t addrstart, uint32_t addrend, bool is_write)
{
if (bank.m_memory != nullptr)
{
// this bank is a memory bank - first lets adjust the length as per the offset; as
// passed to this method, the length is from offset zero
if (length != ~0)
length -= std::min(offset, length);
// do we even have a bank? and if so, have legit changes occured?
if (!memory_bank || !memory_bank->matches_exactly(addrstart, addrend) || (length != m_length))
{
// name the bank
auto tag = string_format("bank%04X_%c", addrstart, is_write ? 'w' : 'r');
// determine "nop_addrstart" - where the bank ends, and above which is AM_NOP
uint32_t nop_addrstart = (length != ~0)
? std::min(addrend + 1, addrstart + length)
: addrend + 1;
// install the bank
if (is_write)
{
if (addrstart < nop_addrstart)
cpu_space().install_write_bank(addrstart, nop_addrstart - 1, 0, tag.c_str());
if (nop_addrstart <= addrend)
cpu_space().nop_write(nop_addrstart, addrend);
}
else
{
if (addrstart < nop_addrstart)
cpu_space().install_read_bank(addrstart, nop_addrstart - 1, 0, tag.c_str());
if (nop_addrstart <= addrend)
cpu_space().nop_read(nop_addrstart, addrend);
}
m_length = length;
// and get it
memory_bank = cpu_space().device().owner()->membank(tag.c_str());
}
// point the bank
if (memory_bank != nullptr)
{
if (is_write && bank.m_memory_read_only)
memory_bank->set_base(m_owner.m_dummy);
else
memory_bank->set_base(bank.m_memory + offset);
}
}
else
{
// this bank uses handlers - first thing's first, assert that we are not doing
// any weird stuff with offfsets and lengths - that isn't supported in this path
assert((offset == 0) && (length == (uint32_t)~0));
if (is_write)
{
if (!bank.m_whandler.isnull())
cpu_space().install_write_handler(addrstart, addrend, bank.m_whandler);
}
else
{
if (!bank.m_rhandler.isnull())
cpu_space().install_read_handler(addrstart, addrend, bank.m_rhandler);
}
}
}