51 lines
1.3 KiB
C
51 lines
1.3 KiB
C
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#include "fakelib.h"
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#include "timer.h"
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void fakelib_shutup() {
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outportb(0x61, inportb(0x61) & 0xfc);
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}
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void fakelib_init() {
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atexit(fakelib_shutup);
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}
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static unsigned int remaining_ticks;
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static unsigned int last_tick;
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static unsigned int fnumlow;
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void fakelib_write(int reg, int val) {
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if (reg == 0xa0) { // writing a new frequency to voice 0
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fnumlow = (val & 0xff);
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} else if (reg == 0xb0) {
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if (val & 0x20) {
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unsigned long fnum = ((val & 0x03) << 8) | fnumlow;
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unsigned int oct = (val & 0x1c) >> 2;
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unsigned long div = (24L << (20 - oct)) / fnum;
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unsigned char tmp;
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outportb(0x43, 0xb6);
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outportb(0x42, div & 0xff);
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outportb(0x42, (div >> 8) & 0xff);
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outportb(0x61, inportb(0x61) | 0x03);
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// todo: guess at duration based on instrument decay
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remaining_ticks = 2;
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last_tick = timer_counter;
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} else {
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fakelib_shutup();
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remaining_ticks = 0;
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}
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}
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}
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void fakelib_tick() {
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if (remaining_ticks > 0) {
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unsigned int tickdiff = timer_counter - last_tick;
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if (tickdiff >= remaining_ticks) {
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fakelib_shutup();
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remaining_ticks = 0;
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} else {
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remaining_ticks -= tickdiff;
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}
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}
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last_tick = timer_counter;
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}
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