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[m6526] implement TOD and alarm #85

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[m6526] implement TOD and alarm #85

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e55bf3d
[m6526] implement TOD and alarm
nippur72 Aug 8, 2023
fb6eab2
fix CIA TOD to pass all VICE tests
nippur72 Aug 10, 2023
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164 changes: 163 additions & 1 deletion chips/m6526.h
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Original file line number Diff line number Diff line change
Expand Up @@ -241,12 +241,38 @@ typedef struct {
bool flag; // last state of flag bit, to detect edge
} m6526_int_t;

// TOD state
typedef struct {
bool running;
bool latched;
bool alarm;

uint8_t tenths;
uint8_t seconds;
uint8_t minutes;
uint8_t hours;

uint8_t latched_tenths;
uint8_t latched_seconds;
uint8_t latched_minutes;
uint8_t latched_hours;

uint8_t alarm_tenths;
uint8_t alarm_seconds;
uint8_t alarm_minutes;
uint8_t alarm_hours;

uint8_t counter;
uint8_t match_counter;
} m6526_tod_t;

// m6526 state
typedef struct {
m6526_port_t pa;
m6526_port_t pb;
m6526_timer_t ta;
m6526_timer_t tb;
m6526_tod_t tod;
m6526_int_t intr;
uint64_t pins;
} m6526_t;
Expand Down Expand Up @@ -309,13 +335,37 @@ static void _m6526_init_interrupt(m6526_int_t* intr) {
intr->flag = false;
}

static void _m6526_init_tod(m6526_tod_t* tod) {
tod->tenths = 0x0;
tod->seconds = 0x00;
tod->minutes = 0x00;
tod->hours = 0x01; // the most common value

tod->latched_tenths = 0x0;
tod->latched_seconds = 0x00;
tod->latched_minutes = 0x00;
tod->latched_hours = 0x01;

tod->alarm_tenths = 0x0;
tod->alarm_seconds = 0x00;
tod->alarm_minutes = 0x00;
tod->alarm_hours = 0x00;

tod->running = false;
tod->latched = false;
tod->alarm = false;
tod->counter = 0;
tod->match_counter = 5;
}

void m6526_init(m6526_t* c) {
CHIPS_ASSERT(c);
memset(c, 0, sizeof(*c));
_m6526_init_port(&c->pa);
_m6526_init_port(&c->pb);
_m6526_init_timer(&c->ta);
_m6526_init_timer(&c->tb);
_m6526_init_tod(&c->tod);
_m6526_init_interrupt(&c->intr);
c->ta.latch = 0xFFFF;
c->tb.latch = 0xFFFF;
Expand All @@ -327,6 +377,7 @@ void m6526_reset(m6526_t* c) {
_m6526_init_port(&c->pb);
_m6526_init_timer(&c->ta);
_m6526_init_timer(&c->tb);
_m6526_init_tod(&c->tod);
_m6526_init_interrupt(&c->intr);
c->pins = 0;
}
Expand Down Expand Up @@ -447,7 +498,17 @@ static uint64_t _m6526_update_irq(m6526_t* c, uint64_t pins) {
}
c->intr.flag = 0 != (pins & M6526_FLAG);

/* FIXME: ALARM, SP interrupt conditions */
/* FIXME: SP interrupt conditions */

// set alarm bit only on the raising edge of the alarm signal
bool alarm = (
c->tod.tenths == c->tod.alarm_tenths &&
c->tod.seconds == c->tod.alarm_seconds &&
c->tod.minutes == c->tod.alarm_minutes &&
c->tod.hours == c->tod.alarm_hours
);
if(alarm && !c->tod.alarm) c->intr.icr |= (1<<2);
c->tod.alarm = alarm;

/* handle main interrupt bit */
if (_M6526_PIP_TEST(c->intr.pip, M6526_PIP_IRQ, 0)) {
Expand Down Expand Up @@ -559,10 +620,57 @@ static void _m6526_tick_pipeline(m6526_t* c) {
c->intr.pip = (c->intr.pip >> 1) & 0x7F7F7F7F;
}

#define BCDINC(x) ((((x)+1) & 0xF) == 0x0A ? (x)+7 : (((x) & 0x0F) == 0x0F ? (x) & 0xF0 : ((x)+1)))

static void _m6526_tick_tod(m6526_tod_t* tod, uint64_t pins) {
if(!(pins & M6526_TOD) || !tod->running) return;

// convert TOD 50/60 Hz signal to 10 Hz
tod->counter = (tod->counter + 1) & 0x07;
if(tod->counter != tod->match_counter) return;
tod->counter = 0;

// unpack from BCD
uint8_t tenths = tod->tenths;
uint8_t seconds = tod->seconds;
uint8_t minutes = tod->minutes;
uint8_t hours = tod->hours;

// increment clock
tenths = (tenths + 1) & 0x0F;
if(tenths == 10) {
tenths = 0;
seconds = BCDINC(seconds) & 0x7F;
if(seconds == 0x60) {
seconds = 0;
minutes = BCDINC(minutes) & 0x7F;
if(minutes == 0x60) {
minutes = 0;
++hours;
if(hours == 0x13) hours = 0x01;
else if(hours == 0x0A) hours = 0x10;
else if(hours == 0x12) hours = 0x92;
else if(hours == 0x93) hours = 0x81;
else if(hours == 0x8A) hours = 0x90;
else if(hours == 0x92) hours = 0x12;
else if(hours == 0x10) hours = 0x00;
else if(hours == 0x20) hours = 0x10;
}
}
}

// pack into BCD
tod->tenths = tenths;
tod->seconds = seconds;
tod->minutes = minutes;
tod->hours = hours;
}

static uint64_t _m6526_tick(m6526_t* c, uint64_t pins) {
_m6526_read_port_pins(c, pins);
_m6526_tick_timer(&c->ta);
_m6526_tick_timer(&c->tb);
_m6526_tick_tod(&c->tod, pins);
pins = _m6526_update_irq(c, pins);
pins = _m6526_write_port_pins(c, pins);
_m6526_tick_pipeline(c);
Expand Down Expand Up @@ -616,6 +724,26 @@ static uint8_t _m6526_read(m6526_t* c, uint8_t addr) {
/* force-load bit always returns zero */
data = c->tb.cr & ~(1<<4);
break;
case M6526_REG_TOD10TH:
data = c->tod.latched ? c->tod.latched_tenths : c->tod.tenths;
c->tod.latched = false;
break;
case M6526_REG_TODSEC:
data = c->tod.latched ? c->tod.latched_seconds : c->tod.seconds;
break;
case M6526_REG_TODMIN:
data = c->tod.latched ? c->tod.latched_minutes : c->tod.minutes;
break;
case M6526_REG_TODHR:
if(!c->tod.latched) {
c->tod.latched_tenths = c->tod.tenths;
c->tod.latched_seconds = c->tod.seconds;
c->tod.latched_minutes = c->tod.minutes;
c->tod.latched_hours = c->tod.hours;
c->tod.latched = true;
}
data = c->tod.latched ? c->tod.latched_hours : c->tod.hours;
break;
}
return data;
}
Expand Down Expand Up @@ -659,10 +787,44 @@ static void _m6526_write(m6526_t* c, uint8_t addr, uint8_t data) {
break;
case M6526_REG_CRA:
_m6526_write_cr(&c->ta, data);
c->tod.match_counter = data & (1<<7) ? 5 : 6; // 50 or 60 Hz TOD
break;
case M6526_REG_CRB:
_m6526_write_cr(&c->tb, data);
break;
case M6526_REG_TOD10TH:
if(c->tb.cr & (1<<7)) {
c->tod.alarm_tenths = data & 0x0F;
} else {
c->tod.tenths = data & 0x0F;
c->tod.running = true; // TOD starts when tenths are R/W
}
break;
case M6526_REG_TODSEC:
if(c->tb.cr & (1<<7)) {
c->tod.alarm_seconds = data & 0x7F;
} else {
c->tod.seconds = data & 0x7F;
}
break;
case M6526_REG_TODMIN:
if(c->tb.cr & (1<<7)) {
c->tod.alarm_minutes = data & 0x7F;
} else {
c->tod.minutes = data & 0x7F;
}
break;
case M6526_REG_TODHR:
data = data & 0x9F;
if(data == 0x92 || data == 0x12) data ^= 0x80; // CIA oddity: AM/PM flag is inverted at 12 hour
if(c->tb.cr & (1<<7)) {
c->tod.alarm_hours = data;
} else {
c->tod.hours = data;
c->tod.running = false; // TOD stops when hours are written
c->tod.counter = 0;
}
break;
}
}

Expand Down