1/* Copyright (c) 2013-2016 Jeffrey Pfau
  2 *
  3 * This Source Code Form is subject to the terms of the Mozilla Public
  4 * License, v. 2.0. If a copy of the MPL was not distributed with this
  5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
  6#include <mgba/internal/gb/timer.h>
  7
  8#include <mgba/internal/sm83/sm83.h>
  9#include <mgba/internal/gb/gb.h>
 10#include <mgba/internal/gb/io.h>
 11#include <mgba/internal/gb/serialize.h>
 12
 13void _GBTimerIRQ(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 14	UNUSED(timing);
 15	UNUSED(cyclesLate);
 16	struct GBTimer* timer = context;
 17	timer->p->memory.io[REG_TIMA] = timer->p->memory.io[REG_TMA];
 18	timer->p->memory.io[REG_IF] |= (1 << GB_IRQ_TIMER);
 19	GBUpdateIRQs(timer->p);
 20}
 21
 22static void _GBTimerDivIncrement(struct GBTimer* timer, uint32_t cyclesLate) {
 23	while (timer->nextDiv >= GB_DMG_DIV_PERIOD) {
 24		timer->nextDiv -= GB_DMG_DIV_PERIOD;
 25
 26		// Make sure to trigger when the correct bit is a falling edge
 27		if (timer->timaPeriod > 0 && (timer->internalDiv & (timer->timaPeriod - 1)) == timer->timaPeriod - 1) {
 28			++timer->p->memory.io[REG_TIMA];
 29			if (!timer->p->memory.io[REG_TIMA]) {
 30				mTimingSchedule(&timer->p->timing, &timer->irq, 7 - ((timer->p->cpu->executionState - cyclesLate) & 3));
 31			}
 32		}
 33		unsigned timingFactor = 0x3FF >> !timer->p->doubleSpeed;
 34		if ((timer->internalDiv & timingFactor) == timingFactor) {
 35			GBAudioUpdateFrame(&timer->p->audio, &timer->p->timing);
 36		}
 37		++timer->internalDiv;
 38		timer->p->memory.io[REG_DIV] = timer->internalDiv >> 4;
 39	}
 40}
 41
 42void _GBTimerUpdate(struct mTiming* timing, void* context, uint32_t cyclesLate) {
 43	struct GBTimer* timer = context;
 44	timer->nextDiv += cyclesLate;
 45	_GBTimerDivIncrement(timer, cyclesLate);
 46	// Batch div increments
 47	int divsToGo = 16 - (timer->internalDiv & 15);
 48	int timaToGo = INT_MAX;
 49	if (timer->timaPeriod) {
 50		timaToGo = timer->timaPeriod - (timer->internalDiv & (timer->timaPeriod - 1));
 51	}
 52	if (timaToGo < divsToGo) {
 53		divsToGo = timaToGo;
 54	}
 55	timer->nextDiv = GB_DMG_DIV_PERIOD * divsToGo;
 56	mTimingSchedule(timing, &timer->event, timer->nextDiv - cyclesLate);
 57}
 58
 59void GBTimerReset(struct GBTimer* timer) {
 60	timer->event.context = timer;
 61	timer->event.name = "GB Timer";
 62	timer->event.callback = _GBTimerUpdate;
 63	timer->event.priority = 0x20;
 64	timer->irq.context = timer;
 65	timer->irq.name = "GB Timer IRQ";
 66	timer->irq.callback = _GBTimerIRQ;
 67	timer->event.priority = 0x21;
 68
 69	timer->nextDiv = GB_DMG_DIV_PERIOD; // TODO: GBC differences
 70	timer->timaPeriod = 1024 >> 4;
 71}
 72
 73void GBTimerDivReset(struct GBTimer* timer) {
 74	timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
 75	mTimingDeschedule(&timer->p->timing, &timer->event);
 76	_GBTimerDivIncrement(timer, 0);
 77	if (((timer->internalDiv << 1) | ((timer->nextDiv >> 3) & 1)) & timer->timaPeriod) {
 78		++timer->p->memory.io[REG_TIMA];
 79		if (!timer->p->memory.io[REG_TIMA]) {
 80			mTimingSchedule(&timer->p->timing, &timer->irq, 7 - (timer->p->cpu->executionState & 3));
 81		}
 82	}
 83	unsigned timingFactor = 0x400 >> !timer->p->doubleSpeed;
 84	if (timer->internalDiv & timingFactor) {
 85		GBAudioUpdateFrame(&timer->p->audio, &timer->p->timing);
 86	}
 87	timer->p->memory.io[REG_DIV] = 0;
 88	timer->internalDiv = 0;
 89	timer->nextDiv = GB_DMG_DIV_PERIOD;
 90	mTimingSchedule(&timer->p->timing, &timer->event, timer->nextDiv - ((timer->p->cpu->executionState + 1) & 3));
 91}
 92
 93uint8_t GBTimerUpdateTAC(struct GBTimer* timer, GBRegisterTAC tac) {
 94	if (GBRegisterTACIsRun(tac)) {
 95		timer->nextDiv -= mTimingUntil(&timer->p->timing, &timer->event);
 96		mTimingDeschedule(&timer->p->timing, &timer->event);
 97		_GBTimerDivIncrement(timer, (timer->p->cpu->executionState + 2) & 3);
 98
 99		switch (GBRegisterTACGetClock(tac)) {
100		case 0:
101			timer->timaPeriod = 1024 >> 4;
102			break;
103		case 1:
104			timer->timaPeriod = 16 >> 4;
105			break;
106		case 2:
107			timer->timaPeriod = 64 >> 4;
108			break;
109		case 3:
110			timer->timaPeriod = 256 >> 4;
111			break;
112		}
113
114		timer->nextDiv += GB_DMG_DIV_PERIOD;
115		mTimingSchedule(&timer->p->timing, &timer->event, timer->nextDiv);
116	} else {
117		timer->timaPeriod = 0;
118	}
119	return tac;
120}
121
122void GBTimerSerialize(const struct GBTimer* timer, struct GBSerializedState* state) {
123	STORE_32LE(timer->nextDiv, 0, &state->timer.nextDiv);
124	STORE_32LE(timer->internalDiv, 0, &state->timer.internalDiv);
125	STORE_32LE(timer->timaPeriod, 0, &state->timer.timaPeriod);
126	STORE_32LE(timer->event.when - mTimingCurrentTime(&timer->p->timing), 0, &state->timer.nextEvent);
127	STORE_32LE(timer->irq.when - mTimingCurrentTime(&timer->p->timing), 0, &state->timer.nextIRQ);
128	GBSerializedTimerFlags flags = GBSerializedTimerFlagsSetIrqPending(0, mTimingIsScheduled(&timer->p->timing, &timer->irq));
129	state->timer.flags = flags;
130}
131
132void GBTimerDeserialize(struct GBTimer* timer, const struct GBSerializedState* state) {
133	LOAD_32LE(timer->nextDiv, 0, &state->timer.nextDiv);
134	LOAD_32LE(timer->internalDiv, 0, &state->timer.internalDiv);
135	LOAD_32LE(timer->timaPeriod, 0, &state->timer.timaPeriod);
136
137	uint32_t when;
138	LOAD_32LE(when, 0, &state->timer.nextEvent);
139	mTimingSchedule(&timer->p->timing, &timer->event, when);
140
141	GBSerializedTimerFlags flags = state->timer.flags;
142
143	if (GBSerializedTimerFlagsIsIrqPending(flags)) {
144		LOAD_32LE(when, 0, &state->timer.nextIRQ);
145		mTimingSchedule(&timer->p->timing, &timer->irq, when);
146	}
147}