From 030724a9aea346e4a9843d5842fb28c6d6c4cf1a Mon Sep 17 00:00:00 2001 From: Peter Fors Date: Thu, 9 Oct 2025 22:07:52 +0200 Subject: Rearrangement and refactoring and optimizations and more accuracy --- mknes_cpu.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 95 insertions(+) create mode 100644 mknes_cpu.c (limited to 'mknes_cpu.c') diff --git a/mknes_cpu.c b/mknes_cpu.c new file mode 100644 index 0000000..3c0a3f2 --- /dev/null +++ b/mknes_cpu.c @@ -0,0 +1,95 @@ +// NOTE(peter): You can enable decimal mode by adding this to the compilerflags -dENABLE_DECIMAL_MODE DO NOT ENABLE FOR NES!!! + +#define PAGE_CROSSED(base, addr) (((base ^ addr) > 0xff)) + +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; +} + +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 *) __attribute__((aligned(4096))); + +#include "mknes_cpu_opcodes.c" +#include "mknes_cpu_opcodes_ud.c" + +static inline void do_nmi(struct nes_state *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 *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 *state) { + struct cpu_state * restrict cpu = &state->cpu; + + if(state->cpu.nmi_pending) { + state->cpu.nmi_pending = 0; + do_nmi(state); + } else if(state->cpu.irq_pending && cpu->i == 0) { + state->cpu.irq_pending = 0; + do_irq(state); + } +} + + +static inline void cpu_reset(struct nes_state *state) { + uint32_t lo = state->mapper_function.prg_rom_read(state, 0xfffc); + uint32_t hi = state->mapper_function.prg_rom_read(state, 0xfffd); + state->cpu.sp = 0xfd; + state->cpu.i = 1; + state->cpu.pc = (hi << 8) | lo; +} + +static inline void cpu_tick(struct nes_state *state) { + struct cpu_state * restrict cpu = &state->cpu; + check_interrupts(state); + + // printf("%4.4x: ", 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: %ld\n", opcode, cpu->a, cpu->x, cpu->y, pack_flags(cpu), cpu->sp, state->cycles); + opcode_lut[opcode](state); +} -- cgit v1.2.3