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Merged
merged 3 commits into from
Nov 23, 2025
Merged

Improve mos-sim trace ergonomics #417

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436c5cf
Improve mos-sim trace ergonomics
lashtear Nov 20, 2025
3496245
fix buffer termination
lashtear Nov 21, 2025
14317ba
Fixing nits
lashtear Nov 23, 2025
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28 changes: 25 additions & 3 deletions utils/sim/mos-sim.c
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,8 @@ bool input_eof = false;

uint64_t clockTicksAtAddress[65536];

void finish(void);

int8_t read6502(uint16_t address) {
if (address == 0xfff0) {
*((uint32_t *)(memory + address)) = clockticks6502 - clock_start;
Expand All @@ -68,6 +70,10 @@ int8_t read6502(uint16_t address) {
return (int8_t)c;
} else if (address == 0xfff6) {
return (int8_t)input_eof;
} else if (address == 0xfffe) {
fprintf(stderr, "%04x:%02x %02x %02x read fffe\n", pc, memory[pc], memory[pc+1], memory[pc+2]);
finish();
abort();
}
return memory[address];
}
Expand All @@ -91,9 +97,13 @@ void write6502(uint16_t address, uint8_t value) {
clock_start = clockticks6502;
break;
case 0xFFF7:
if (shouldProfile)
fprintf(stderr, "%04x:%02x %02x %02x write fff7\n", pc, memory[pc], memory[pc+1], memory[pc+2]);
finish();
abort();
case 0xFFF8:
if (shouldProfile)
fprintf(stderr, "%04x:%02x %02x %02x write fff7\n", pc, memory[pc], memory[pc+1], memory[pc+2]);
finish();
exit(value);
case 0xFFF9:
Expand Down Expand Up @@ -187,9 +197,21 @@ int main(int argc, const char *argv[]) {

reset6502(cmos);
for (;;) {
if (shouldTrace)
fprintf(stderr, "%04x a:%02x x:%02x y:%02x s: %02x st:%02x\n", pc, a, x,
y, sp, status);
char status_buf[9];
status_buf[8] = '\0';
const char statuses[] = "czidb1vn";

if (shouldTrace) {
for (int i=0; i<8; ++i) {
status_buf[7-i] = status&(1<<i) ?
statuses[i] : '.';
}
fprintf(stderr,
"%04x a:%02x x:%02x y:%02x s:%02x st:%02x (%s)"
" insn:%02x %02x %02x\n",
pc, a, x, y, sp, status, status_buf,
memory[pc], memory[(pc+1)&0xffff], memory[(pc+2)&0xffff]);
}
uint32_t clockTicksBefore = clockticks6502;
uint16_t addr = pc;
step6502();
Expand Down