emu_nes

An NES emulator for learning how the 6502 and similar computers of the era worked
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apu.c (1465B)

      1 #include <stdio.h>
      2 #include <string.h>
      3 
      4 #include "apu.h"
      5 
      6 struct apu apu = {0};
      7 
      8 void
      9 apu_init(void)
     10 {
     11 	memset(&apu, 0, sizeof(apu));
     12 }
     13 
     14 uint8_t
     15 apu_read(uint16_t addr)
     16 {
     17 	switch (addr) {
     18 	/* pulse1 */
     19 	case 0x4000:
     20 		return (apu.pulse1.duty << 6) | (apu.pulse1.envelope << 5)
     21 		    | (apu.pulse1.const_vol << 4) | apu.pulse1.envelope_vol;
     22 	case 0x4001:
     23 		return (apu.pulse1.sweep_enable << 7) | (apu.pulse1.sweep_period << 4)
     24 		    | (apu.pulse1.sweep_negative << 3) | apu.pulse1.sweep_shift_count;
     25 	case 0x4002:
     26 		return apu.pulse1.timer_low;
     27 	case 0x4003:
     28 		return (apu.pulse1.length_counter_load << 3) | apu.pulse1.timer_high;
     29 	/* pulse2 */
     30 	case 0x4004:
     31 		return (apu.pulse2.duty << 6) | (apu.pulse2.envelope << 5)
     32 		    | (apu.pulse2.const_vol << 4) | apu.pulse2.envelope_vol;
     33 	case 0x4005:
     34 		return (apu.pulse1.sweep_enable << 7) | (apu.pulse1.sweep_period << 4)
     35 		    | (apu.pulse1.sweep_negative << 3) | apu.pulse1.sweep_shift_count;
     36 	case 0x4006:
     37 		return apu.pulse1.timer_low;
     38 	case 0x4007:
     39 		return (apu.pulse1.length_counter_load << 3) | apu.pulse1.timer_high;
     40 	/* status */
     41 	case 0x4015:
     42 		return (apu.status.dmc_int << 7) | (apu.status.frame_int << 6)
     43 		    | (apu.status.dmc_active << 4) | (apu.status.lc_noise << 3)
     44 		    | (apu.status.lc_triangle << 2) | (apu.status.lc_pulse2 << 1)
     45 		    | apu.status.lc_pulse1;
     46 	default:
     47 		fprintf(stderr, "Invalid APU read at $%04X!\n", addr);
     48 		return 0;
     49 	};
     50 }
     51 
     52 void
     53 apu_write(uint16_t addr, uint8_t byte)
     54 {
     55 }