add preliminary apu register support

Makefile

@@ -1,7 +1,7 @@
 CFLAGS = -O2 -Wall -Wextra -pedantic -Wno-unused-parameter
 
 nes:
-	${CC} ${CFLAGS} -o nes cpu.c rom.c ppu.c
+	${CC} ${CFLAGS} -o nes cpu.c rom.c ppu.c apu.c
 
 test: nes
 	./nes ${HOME}/src/other/nes-test-roms/other/nestest.nes

apu.c

@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "apu.h"
+
+struct apu apu = {0};
+
+void
+apu_init(void)
+{
+	memset(&apu, 0, sizeof(apu));
+}
+
+uint8_t
+apu_read(uint16_t addr)
+{
+	switch (addr) {
+	/* pulse1 */
+	case 0x4000:
+		return (apu.pulse1.duty << 6) | (apu.pulse1.envelope << 5)
+		    | (apu.pulse1.const_vol << 4) | apu.pulse1.envelope_vol;
+	case 0x4001:
+		return (apu.pulse1.sweep_enable << 7) | (apu.pulse1.sweep_period << 4)
+		    | (apu.pulse1.sweep_negative << 3) | apu.pulse1.sweep_shift_count;
+	case 0x4002:
+		return apu.pulse1.timer_low;
+	case 0x4003:
+		return (apu.pulse1.length_counter_load << 3) | apu.pulse1.timer_high;
+	/* pulse2 */
+	case 0x4004:
+		return (apu.pulse2.duty << 6) | (apu.pulse2.envelope << 5)
+		    | (apu.pulse2.const_vol << 4) | apu.pulse2.envelope_vol;
+	case 0x4005:
+		return (apu.pulse1.sweep_enable << 7) | (apu.pulse1.sweep_period << 4)
+		    | (apu.pulse1.sweep_negative << 3) | apu.pulse1.sweep_shift_count;
+	case 0x4006:
+		return apu.pulse1.timer_low;
+	case 0x4007:
+		return (apu.pulse1.length_counter_load << 3) | apu.pulse1.timer_high;
+	/* status */
+	case 0x4015:
+		return (apu.status.dmc_int << 7) | (apu.status.frame_int << 6)
+		    | (apu.status.dmc_active << 4) | (apu.status.lc_noise << 3)
+		    | (apu.status.lc_triangle << 2) | (apu.status.lc_pulse2 << 1)
+		    | apu.status.lc_pulse1;
+	default:
+		fprintf(stderr, "Invalid APU read at $%04X!\n", addr);
+		return 0;
+	};
+}
+
+void
+apu_write(uint16_t addr, uint8_t byte)
+{
+}

apu.h

@@ -0,0 +1,105 @@
+#ifndef APU_H
+#define APU_H
+
+#include <stdint.h>
+
+struct pulse {
+	/* $4000/$4004 */
+	uint8_t duty : 2;
+	uint8_t envelope : 1;
+	uint8_t const_vol : 1;
+	uint8_t envelope_vol : 4;
+	/* $4001/$4005 */
+	uint8_t sweep_enable : 1;
+	uint8_t sweep_period : 3;
+	uint8_t sweep_negative : 1;
+	uint8_t sweep_shift_count : 3;
+	/* $4002/$4006 */
+	uint8_t timer_low;
+	/* $4003/$4007 */
+	uint8_t length_counter_load : 5;
+	uint8_t timer_high : 3;
+};
+
+struct triangle {
+	/* $4008 */
+	uint8_t counter_disable : 1;
+	uint8_t counter_reload : 7;
+	/* $400A */
+	uint8_t timer_low;
+	/* $400B */
+	uint8_t counter_load : 5;
+	uint8_t timer_high : 3;
+};
+
+struct noise {
+	/* $400C */
+	uint8_t padding1 : 2;
+	uint8_t loop_envelope : 1;
+	uint8_t constant_volume : 1;
+	uint8_t envelope_volume : 4;
+	/* $400E */
+	uint8_t loop_noise : 1;
+	uint8_t padding2 : 3;
+	uint8_t noise_period : 4;
+	/* $400F */
+	uint8_t length_counter_load : 5;
+	uint8_t padding3 : 3;
+};
+
+struct dmc {
+	/* $4010 */
+	uint8_t irq_enable : 1;
+	uint8_t loop : 1;
+	uint8_t padding1 : 2;
+	uint8_t frequency : 4;
+	/* $4011 */
+	uint8_t padding2 : 1;
+	uint8_t load_counter : 7;
+	/* $4012 */
+	uint8_t sample_addr;
+	/* $4013 */
+	uint8_t sample_length;
+};
+
+struct apu {
+	/* $4000-$4013 (write) */
+	struct pulse pulse1;
+	struct pulse pulse2;
+	struct triangle triangle;
+	struct noise noise;
+	struct dmc dmc;
+	/* $4015 (write) */
+	struct control {
+		uint8_t padding : 3;
+		uint8_t dmc_enable : 1;
+		uint8_t noise_enable : 1;
+		uint8_t triangle_enable : 1;
+		uint8_t pulse2_enable : 1;
+		uint8_t pulse1_enable : 1;
+	} control;
+	/* $4015 (read) */
+	struct status {
+		uint8_t dmc_int : 1;
+		uint8_t frame_int : 1;
+		uint8_t padding : 1;
+		uint8_t dmc_active : 1;
+		uint8_t lc_noise : 1;
+		uint8_t lc_triangle : 1;
+		uint8_t lc_pulse2 : 1;
+		uint8_t lc_pulse1 : 1;
+	} status;
+	/* $4017 (write) */
+	struct frame_counter {
+		uint8_t mode : 1;
+		uint8_t irq_inhibit : 1;
+		uint8_t padding : 6;
+	} frame_counter;
+};
+extern struct apu apu;
+
+void apu_tick(void);
+uint8_t apu_read(uint16_t addr);
+void apu_write(uint16_t addr, uint8_t byte);
+
+#endif /* APU_H */

cpu.c

@@ -5,10 +5,11 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include "apu.h"
 #include "cpu.h"
 #include "opcodes.h"
-#include "rom.h"
 #include "ppu.h"
+#include "rom.h"
 
 #define MAX(a, b)	((a > b) ? a : b)
 
@@ -53,10 +54,11 @@ peek(uint16_t addr)
 			return rom.prg_rom[addr - 0x8000];
 		else
 			fprintf(stderr, "PRG ROG size is not 0x4000 nor 0x8000\n"), exit(1);
-	} else {
+	} else if ((addr >= 0x4000 && addr <= 0x4013) || addr == 0x4015 || addr == 0x4017)
+		return apu_read(addr);
+	else
 		return memory[addr];
 }
-}
 
 static uint16_t
 peek16(uint16_t addr)
@@ -68,6 +70,11 @@ peek16(uint16_t addr)
 static void
 memwrite(uint16_t addr, uint8_t byte)
 {
+	if (addr >= 0x4000 && addr <= 0x4017) {
+		apu_write(addr, byte);
+		return;
+	}
+
 	MEMORY_MIRROR(addr);
 
 	memory[addr] = byte;