1 files changed, 101 insertions, 0 deletions
diff --git a/cpu.c b/cpu.c
new file mode 100644
index 0000000..3e731e5
--- /dev/null
+++ b/cpu.c
@@ -0,0 +1,101 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+// REMOVE FOR NES!!!!!
+// #define ENABLE_DECIMAL_MODE
+
+__attribute__((always_inline))
+static inline uint8_t pack_flags(struct cpu_state *cpu) {
+	return (cpu->n << 7) | (cpu->v << 6) | (1 << 5) | (cpu->d << 3) | (cpu->i << 2) | (cpu->z << 1) | cpu->c;
+}
+
+__attribute__((always_inline))
+static inline void unpack_flags(struct cpu_state *cpu, uint8_t value) {
+	cpu->n = (value >> 7) & 1;
+	cpu->v = (value >> 6) & 1;
+	cpu->d = (value >> 3) & 1;
+	cpu->i = (value >> 2) & 1;
+	cpu->z = (value >> 1) & 1;
+	cpu->c = value & 1;
+}
+
+
+static inline void update_zn(struct cpu_state *cpu, uint8_t result) {
+	cpu->z = (result == 0);
+	cpu->n = (result & 0x80) != 0;
+}
+
+
+
+static void (*opcode_lut[256])(struct nes_state *state);
+
+uint32_t line = 1;
+
+struct addr_result {
+	uint32_t addr;
+	uint8_t value;
+};
+#include "cpu_opcodes.c"
+#include "cpu_opcodes_ud.c"
+
+static inline void do_nmi(struct nes_state * restrict state) {
+	struct cpu_state * restrict cpu = &state->cpu;
+
+	memory_read_dummy(state, cpu->pc);		// T1: dummy read (fetch suppressed)
+
+	uint8_t pcl = cpu->pc & 0xff;
+	uint8_t pch = cpu->pc >> 8;
+
+	memory_write(state, 0x0100 + cpu->sp--, pch);	// T2
+	memory_write(state, 0x0100 + cpu->sp--, pcl);	// T3
+	memory_write(state, 0x0100 + cpu->sp--, pack_flags(cpu) & ~0x10);	// T4: push P (B flag clear)
+
+	uint8_t lo = memory_read(state, 0xfffa);	// T5
+	uint8_t hi = memory_read(state, 0xfffb);	// T6
+
+	cpu->pc = lo | (hi << 8);			// T7
+	cpu->i = 1;
+}
+
+static inline void do_irq(struct nes_state * restrict state) {
+	struct cpu_state * restrict cpu = &state->cpu;
+
+	memory_read_dummy(state, cpu->pc);		// T1: dummy read (fetch suppressed)
+
+	uint8_t pcl = cpu->pc & 0xff;
+	uint8_t pch = cpu->pc >> 8;
+
+	memory_write(state, 0x0100 + cpu->sp--, pch);	// T2
+	memory_write(state, 0x0100 + cpu->sp--, pcl);	// T3
+	memory_write(state, 0x0100 + cpu->sp--, pack_flags(cpu) & ~0x10);	// T4: push P (B flag clear)
+
+	uint8_t lo = memory_read(state, 0xfffe);	// T5
+	uint8_t hi = memory_read(state, 0xffff);	// T6
+
+	cpu->pc = lo | (hi << 8);			// T7
+	cpu->i = 1;
+}
+
+static inline void check_interrupts(struct nes_state * restrict state) {
+	struct cpu_state * restrict cpu = &state->cpu;
+
+	if(state->nmi_pending) {
+		state->nmi_pending = 0;
+		do_nmi(state);
+	} else if(state->irq_pending && cpu->i == 0) {
+		do_irq(state);
+	}
+}
+
+static void cpu_tick(struct nes_state *state) {
+	struct cpu_state * restrict cpu = &state->cpu;
+
+	check_interrupts(state);
+
+	// printf("%5.5d %4.4x: ", line++, cpu->pc);
+	uint8_t opcode = memory_read(state, cpu->pc++);
+	// printf("%2.2x   a:%2.2x x:%2.2x y:%2.2x p:%2.2x sp:%2.2x  cycle: %d\n", opcode, cpu->a, cpu->x, cpu->y, pack_flags(cpu), cpu->sp, cycle);
+	opcode_lut[opcode](state);
+
+}