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Fixes #5 - Support interrupts

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This commit is contained in:
Stefan Arentz 2016-11-13 20:07:54 -05:00
parent e7ed556023
commit 85c8204c1b
3 changed files with 47 additions and 3 deletions
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37
cpu.c
View File

@ -80,6 +80,33 @@ uint16_t _cpu_pull_word(struct cpu_t *cpu) {
return (uint16_t) _cpu_pull_byte(cpu) | ((uint16_t) _cpu_pull_byte(cpu) << 8);
}
// Because we keep the processor status bits in separate fields, we
// need a function to combine them into a single register. This is
// only used when we need to push the register on the stack for
// interupt handlers. If this turns out to be inefficient then they
// can be stored in their native form in a byte.
uint8_t _cpu_get_status(struct cpu_t *cpu) {
return 0x30
| (((cpu->state.n != 0) & 0x01) << 7)
| (((cpu->state.v != 0) & 0x01) << 6)
| (((cpu->state.b != 0) & 0x01) << 4)
| (((cpu->state.d != 0) & 0x01) << 3)
| (((cpu->state.i != 0) & 0x01) << 2)
| (((cpu->state.z != 0) & 0x01) << 1)
| (((cpu->state.c != 0) & 0x01) << 0);
}
void _cpu_set_status(struct cpu_t *cpu, uint8_t status) {
cpu->state.n = (status & (1 << 7));
cpu->state.v = (status & (1 << 6));
cpu->state.b = (status & (1 << 4));
cpu->state.d = (status & (1 << 3));
cpu->state.i = (status & (1 << 2));
cpu->state.z = (status & (1 << 1));
cpu->state.c = (status & (1 << 0));
}
#if 1
static void cpu_format_instruction(struct cpu_t *cpu, char *buffer) {
*buffer = 0x00;
@ -353,11 +380,17 @@ void cpu_reset(struct cpu_t *cpu) {
}
void cpu_irq(struct cpu_t *cpu) {
/* TODO: Implement support for IRQ triggering */
_cpu_push_word(cpu, cpu->state.pc);
_cpu_push_byte(cpu, _cpu_get_status(cpu));
cpu->state.i = 1;
cpu->state.pc = _mem_get_word(cpu, 0xfffe);
}
void cpu_nmi(struct cpu_t *cpu) {
/* TODO: Implement support for interrupt triggering */
_cpu_push_word(cpu, cpu->state.pc);
_cpu_push_byte(cpu, _cpu_get_status(cpu));
cpu->state.i = 1;
cpu->state.pc = _mem_get_word(cpu, 0xfffa);
}
void cpu_run(struct cpu_t *cpu) {

4
cpu.h
View File

@ -59,6 +59,10 @@ void _cpu_push_word(struct cpu_t *cpu, uint16_t w);
uint8_t _cpu_pull_byte(struct cpu_t *cpu);
uint16_t _cpu_pull_word(struct cpu_t *cpu);
// Private. How do we keep them private?
uint8_t _cpu_get_status(struct cpu_t *cpu);
void _cpu_set_status(struct cpu_t *cpu, uint8_t status);
typedef uint8_t (*iom_read_handler_t)(struct cpu_t *cpu, void *obj, uint16_t addr);
typedef void (*iom_write_handler_t)(struct cpu_t *cpu, void *obj, uint16_t addr, uint8_t b);

9
ins.c
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@ -680,6 +680,13 @@ static void ror_absx(struct cpu_t *cpu, uint16_t oper) {
mem_mod_byte_absx(cpu, oper, ror);
}
/* RTI */
static void rti(struct cpu_t *cpu) {
_cpu_set_status(cpu, _cpu_pull_byte(cpu));
cpu->state.pc = _cpu_pull_word(cpu);
}
/* RTS */
static void rts(struct cpu_t *cpu) {
@ -888,7 +895,7 @@ cpu_instruction_t instructions[256] = {
/* 0x3e */ { "ROL", 0x3e, 3, 7, (void*) rol_absx },
/* 0x3f */ { "???", 0x3f, 1, 2, (void*) unknown_instruction },
/* 0x40 */ { "???", 0x40, 1, 2, (void*) unknown_instruction },
/* 0x40 */ { "RTI", 0x40, 1, 6, (void*) rti },
/* 0x41 */ { "EOR", 0x41, 2, 6, (void*) eor_indx },
/* 0x42 */ { "???", 0x42, 1, 2, (void*) unknown_instruction },
/* 0x43 */ { "???", 0x43, 1, 2, (void*) unknown_instruction },