diff options
| author | Ian Moffett <ian@osmora.org> | 2025-07-22 01:39:53 -0400 |
|---|---|---|
| committer | Ian Moffett <ian@osmora.org> | 2025-07-22 01:40:22 -0400 |
| commit | af93dd2857940d2f0a19481f37ccdb25656ae15d (patch) | |
| tree | b18c253aa9f07b53a1293cd3988fee296cfe5209 | |
| parent | df9f396017f92ad4647697d461bb5475d6596cfb (diff) | |
oemu: cpu: Introduce decoding logic for SUB
Signed-off-by: Ian Moffett <ian@osmora.org>
| -rw-r--r-- | usr.bin/oemu/cpu.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/usr.bin/oemu/cpu.c b/usr.bin/oemu/cpu.c index 8ec106a..84f04bf 100644 --- a/usr.bin/oemu/cpu.c +++ b/usr.bin/oemu/cpu.c @@ -123,6 +123,29 @@ cpu_add(struct oemu_cpu *cpu, inst_t *inst) } /* + * Decode the INST_SUB instruction + * + * @cpu: CPU that is executing + * @inst: Instruction dword + */ +static void +cpu_sub(struct oemu_cpu *cpu, inst_t *inst) +{ + struct cpu_regs *regs = &cpu->regs; + imm_t imm; + + if (inst->rd > NELEM(regs->xreg)) { + printf("bad register operand for 'sub'\n"); + return; + } + + imm = regs->xreg[inst->rd]; + regs->xreg[inst->rd] -= inst->imm; + printf("%d - %d -> X%d, new=%d\n", + imm, inst->imm, inst->rd, regs->xreg[inst->rd]); +} + +/* * Reset a CPU to a default state */ void @@ -161,6 +184,9 @@ cpu_kick(struct oemu_cpu *cpu, struct sysmem *mem) case INST_ADD: cpu_add(cpu, inst); break; + case INST_SUB: + cpu_sub(cpu, inst); + break; } /* Is this a halt instruction? */ |