140 lines
2.8 KiB
C
140 lines
2.8 KiB
C
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#include <timer.h>
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#include <interrupts.h>
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#include <audio.h>
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static timer_context ctx = {0};
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bool selected_bit() {
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switch(ctx.tac & 0b11) {
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case 0b00:
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return (ctx.div & (1 << 9));
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break;
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case 0b01:
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return (ctx.div & (1 << 3));
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break;
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case 0b10:
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return (ctx.div & (1 << 5));
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break;
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case 0b11:
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return (ctx.div & (1 << 7));
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break;
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}
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}
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void inc_tima() {
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ctx.tima++;
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if(ctx.tima == 0x00){
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ctx.tima_needs_reset = true;
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}
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}
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void timer_init() {
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ctx.div = 0XAC00;
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ctx.tac = 0xF8;
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}
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void timer_tick() {
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u16 prev_div = ctx.div;
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bool old = selected_bit();
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ctx.div++;
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bool new = selected_bit();
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if((prev_div & (1 << 1)) && (!(ctx.div & (1 << 1)))){
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if(ctx.tima_just_reset)
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ctx.tima_just_reset = false;
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if(ctx.tima_needs_reset){
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ctx.tima = ctx.tma;
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ctx.tima_needs_reset = false;
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ctx.tima_just_reset = true;
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cpu_request_interrupt(IT_TIMER);
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}
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}
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if(ctx.tac & 0b100 && old && !new) {
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inc_tima();
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}
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audio_sample_tick();
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if((prev_div & (1 << 12)) && (!(ctx.div & (1 << 12)))){
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audio_tick();
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}
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if((prev_div & (1 << 0)) && (!(ctx.div & (1 << 0)))){
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audio_period_tick();
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}
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}
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void timer_write(u16 address, u8 value){
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switch(address) {
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case 0xFF04:
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//DIV
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if(selected_bit()) {
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inc_tima();
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}
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ctx.div = 0;
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break;
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case 0xFF05:
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//TIMA
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if(ctx.tima_just_reset)
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return;
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ctx.tima_needs_reset = false;
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ctx.tima = value;
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break;
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case 0xFF06:
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//TMA
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if(ctx.tima_just_reset)
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ctx.tima = value;
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ctx.tma = value;
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break;
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case 0xFF07:
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//TAC
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bool current = selected_bit();
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bool old_enable = ctx.tac & 0b100;
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ctx.tac = value;
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bool new = selected_bit();
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if(((current && !new) && (ctx.tac & 0b100)) || (current && old_enable && !(ctx.tac & 0b100))) {
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inc_tima();
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}
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break;
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}
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}
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u8 timer_read(u16 address) {
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switch(address) {
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case 0xFF04:
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//DIV
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return ctx.div >> 8;
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case 0xFF05:
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//TIMA
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return ctx.tima;
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case 0xFF06:
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//TMA
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return ctx.tma;
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case 0xFF07:
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//TAC
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return ctx.tac;
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}
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}
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timer_context *timer_get_context() {
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return &ctx;
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}
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void timer_save_state(timer_state* state) {
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state->ctx = ctx;
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}
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void timer_load_state(const timer_state* state) {
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ctx = state->ctx;
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} |