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Make instruction data read more flexible and split from emulation of particular instruction.

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This commit is contained in:
Radosław Kujawa 2017-01-19 10:59:35 +01:00
parent 87cafb607f
commit 49b70f0e1f
3 changed files with 65 additions and 1 deletions
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6
src/emulation.c
View File

@ -8,7 +8,11 @@ emul_lda(rk65c02emu_t *e, instruction_t *i)
instrdef_t id;
id = instruction_decode(i->opcode);
e->regs.A = i->op1;
e->regs.A = instruction_data_read_1(e, &id, i);
/* adjust status flags */
}

59
src/instruction.c
View File

@ -137,3 +137,62 @@ instruction_decode(uint8_t opcode)
return id;
}
uint8_t
instruction_data_read_1(rk65c02emu_t *e, instrdef_t *id, instruction_t *i)
{
uint8_t rv; /* data read from the bus */
// uint8_t ziaddr; /* indirect zero page address */
uint16_t iaddr; /* indirect address */
rv = 0;
switch (id->mode) {
case ACCUMULATOR:
rv = e->regs.A;
break;
case IMMEDIATE:
rv = i->op1;
break;
case ZP:
rv = bus_read_1(e->bus, i->op1);
break;
case ZPX:
/* XXX: wraps around zero page? */
rv = bus_read_1(e->bus, i->op1 + e->regs.X);
break;
case ZPY:
rv = bus_read_1(e->bus, i->op1 + e->regs.Y);
break;
case IZP:
iaddr = bus_read_1(e->bus, i->op1);
iaddr |= (bus_read_1(e->bus, i->op1 + 1) << 8);
rv = bus_read_1(e->bus, iaddr);
break;
case IZPX:
/* ziaddr = bus_read_1(e->bus, i->op1 + e->regs.X);
ziaddr |= (bus_read_1(e->bus, i->op1 + e->regs.X + 1) << 8);
rv = bus_read_1(e->bus, ziaddr);
break;
*/
case IZPY:
/*
iaddr = bus_read_1(e->bus, i->op1 + e->regs.Y);
iaddr |= (bus_read_1(e->bus, i->op1 + e->regs.Y + 1) << 8);
rv = bus_read_1(e->bus, ziaddr);
*/
case RELATIVE:
case ABSOLUTE:
case ABSOLUTEX:
case ABSOLUTEY:
case IABSOLUTE:
case IABSOLUTEX:
default:
printf("unhandled addressing mode for opcode %x\n",
i->opcode);
break;
}
return rv;
}

1
src/instruction.h
View File

@ -43,6 +43,7 @@ instruction_t instruction_fetch(bus_t *, uint16_t);
instrdef_t instruction_decode(uint8_t);
void instruction_print(instruction_t *);
void disassemble(bus_t *, uint16_t);
uint8_t instruction_data_read_1(rk65c02emu_t *, instrdef_t *, instruction_t *);
//void instruction_execute(rk65c02emu_t *, instruction_t *);
#endif /* _INSTRUCTION_H_ */