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+// license:BSD-3-Clause
+// copyright-holders: Angelo Salese
+/**************************************************************************************************
+
+ NEC uPD4991/uPD4991a parallel RTC
+
+ uPD4991 should be very similar but with "30% more power consumption" (cit.)
+
+ TODO:
+ - bare minimum to make PC98HA happy;
+ - set clock regs;
+ - alarm & timer pulse;
+ - AM/PM hour mode;
+ - leap year;
+ - busy flag;
+ - adjust/clock stop/clock wait mechanisms;
+
+**************************************************************************************************/
+
+#include "emu.h"
+#include "machine/upd4991a.h"
+
+
+//*************************************************************************************************
+// GLOBAL VARIABLES
+//*************************************************************************************************
+
+// device type definition
+DEFINE_DEVICE_TYPE(UPD4991A, upd4991a_device, "upd4991a", "NEC uPD4991a parallel RTC")
+
+
+//*************************************************************************************************
+// LIVE DEVICE
+//*************************************************************************************************
+
+//-------------------------------------------------
+// upd4991a_device - constructor
+//-------------------------------------------------
+
+upd4991a_device::upd4991a_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock)
+ : device_t(mconfig, UPD4991A, tag, owner, clock)
+ , device_rtc_interface(mconfig, *this)
+ , m_timer_clock(nullptr)
+{
+ std::fill(std::begin(m_rtc_regs), std::end(m_rtc_regs), 0);
+}
+
+
+//-------------------------------------------------
+// device_validity_check - perform validity checks
+// on this device
+//-------------------------------------------------
+
+void upd4991a_device::device_validity_check(validity_checker &valid) const
+{
+}
+
+
+//-------------------------------------------------
+// device_start - device-specific startup
+//-------------------------------------------------
+
+void upd4991a_device::device_start()
+{
+ m_timer_clock = timer_alloc(TIMER_CLOCK);
+ m_timer_clock->adjust(attotime::from_hz(clock() / 32768), 0, attotime::from_hz(clock() / 32768));
+
+ save_item(NAME(m_address));
+}
+
+
+void upd4991a_device::device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr)
+{
+ switch (id)
+ {
+ case TIMER_CLOCK:
+ advance_seconds();
+ break;
+ }
+}
+
+//-------------------------------------------------
+// rtc_clock_updated -
+//-------------------------------------------------
+
+void upd4991a_device::rtc_clock_updated(int year, int month, int day, int day_of_week, int hour, int minute, int second)
+{
+/*
+[0-1]
+xxxx xxxx seconds
+[2-3]
+xxxx xxxx minutes
+[4-5]
+xxxx xxxx hour
+[6-7]
+---- xxxx date digit (weekday?)
+xxxx ---- 1 day digit
+[8-9]
+---- xxxx 10 day digit
+xxxx ---- 1 month digit
+[a-b]
+---- xxxx 10 month digit
+xxxx ---- 1 year digit
+[c-d]
+---- xxxx 10 year digit
+xxxx ---- control register 1 (write only)
+[e-f]
+---- xxxx control register 2 (read/write)
+xxxx ---- mode register (write only)
+*/
+ m_rtc_regs[0] = convert_to_bcd(second);
+ m_rtc_regs[1] = convert_to_bcd(minute);
+ m_rtc_regs[2] = convert_to_bcd(hour);
+ const u8 bcd_day = convert_to_bcd(day);
+ const u8 bcd_month = convert_to_bcd(month);
+ const u8 bcd_year = convert_to_bcd(year);
+ m_rtc_regs[3] = (day_of_week-1) | ((bcd_day & 0x0f) << 4);
+ m_rtc_regs[4] = ((bcd_day & 0xf0) >> 4) | ((bcd_month & 0x0f) << 4);
+ m_rtc_regs[5] = ((bcd_month & 0xf0) >> 4) | ((bcd_year & 0x0f) << 4);
+ m_rtc_regs[6] = ((bcd_year & 0xf0) >> 4);
+}
+
+//*************************************************************************************************
+// READ/WRITE HANDLERS
+//*************************************************************************************************
+
+u8 upd4991a_device::data_r(offs_t offset)
+{
+ return m_rtc_regs[m_address >> 1] >> ((m_address & 1) ? 4 : 0);
+}
+
+void upd4991a_device::data_w(offs_t offset, u8 data)
+{
+ // ...
+}
+
+void upd4991a_device::address_w(offs_t offset, u8 data)
+{
+ m_address = data & 0xf;
+}