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perf(vcd): stop re-equipping BDMA on every launch when the card already carries a driver pair #243

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Merged
NathanNeurotic merged 1 commit into from
Jul 20, 2026
Merged

perf(vcd): stop re-equipping BDMA on every launch when the card already carries a driver pair #243

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34 changes: 34 additions & 0 deletions src/vcdsupport.c
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Original file line number Diff line number Diff line change
Expand Up @@ -878,6 +878,38 @@ int vcdEquipBdma(int source, int mode, char *diag, int diagSize)
return (mr != 0) ? mr : 0;
}

// 1.0.1-style fast path for the launch equip: a card with NO marker but BOTH driver modules present is
// a pair the user (or an install predating the marker file) manages MANUALLY. vcdReadBdmaMode()
// collapses "marker absent" into VCD_BDMA_FAT32, so before this check every launch on such a card read
// as a MISMATCH and paid the FULL equip -- source-device module loads with bounded waits plus two module
// copies onto the memory card -- on EVERY VCD launch (NathanNeurotic: "unnecessary over work... extended
// wait on game launch... unnecessary MC transfer"). Trust the card and hand off. An EXPLICIT different
// marker (a real variant switch, checked by the caller before this) or a missing/partial pair still does
// the copy work -- ONCE -- after which the marker matches and every later launch takes the cheap path.
static int vcdBdmaManualPairPresent(void)
{
char mcDir[64];
char path[96];
int fd, i;

if (!vcdResolvePopstarterMc(mcDir, sizeof(mcDir)))
return 0;
snprintf(path, sizeof(path), "%s/%s", mcDir, VCD_BDMA_MARKER);
fd = open(path, O_RDONLY);
if (fd >= 0) {
close(fd);
return 0; // marker PRESENT -> its verdict stands (the caller already compared it)
}
Comment on lines +897 to +902

@coderabbitai coderabbitai Bot Jul 20, 2026

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🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

Only treat ENOENT as an absent marker.

A marker open() failure is currently indistinguishable from “no marker.” If the marker exists but the card returns an I/O or access error, this helper can trust an arbitrary module pair and suppress the repair/equip attempt. Return false for all errors other than ENOENT, so the fast path is used only when marker absence is confirmed.

Proposed fix 
     fd = open(path, O_RDONLY);
     if (fd >= 0) {
         close(fd);
         return 0; // marker PRESENT -> its verdict stands (the caller already compared it)
     }
+    if (errno != ENOENT)
+        return 0; // marker state is unknown; do not trust the manual pair
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
snprintf(path, sizeof(path), "%s/%s", mcDir, VCD_BDMA_MARKER);
fd = open(path, O_RDONLY);
if (fd >= 0) {
close(fd);
return 0; // marker PRESENT -> its verdict stands (the caller already compared it)
}
snprintf(path, sizeof(path), "%s/%s", mcDir, VCD_BDMA_MARKER);
fd = open(path, O_RDONLY);
if (fd >= 0) {
close(fd);
return 0; // marker PRESENT -> its verdict stands (the caller already compared it)
}
if (errno != ENOENT)
return 0; // marker state is unknown; do not trust the manual pair
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/vcdsupport.c` around lines 897 - 902, Update the marker check near
VCD_BDMA_MARKER so only an open() failure with errno equal to ENOENT is treated
as marker absence; return 0 immediately for other errors, including I/O or
permission failures. Preserve the existing success path that closes the
descriptor and returns 0 when the marker is present.

for (i = 0; i < 2; i++) {
snprintf(path, sizeof(path), "%s/%s", mcDir, vcdBdmaModule[i]);
fd = open(path, O_RDONLY);
if (fd < 0)
return 0; // pair incomplete -> a real equip is useful work
close(fd);
}
return 1;
}

// Best-effort auto-equip of the device-matching BDMA driver before a VCD launch (POPSLoader's
// ApplyBdmaMode parity). POPSTARTER does its OWN SifIopReset, then reloads its block-device drivers
// from the FIXED memory-card files mc?:/POPSTARTER/usbd.irx + usbhdfsd.irx; equipping copies the
Expand All @@ -901,6 +933,8 @@ void vcdEnsureBdmaForLaunch(int source, int mode)
return; // FAT32 / invalid -> POPSTARTER's built-in driver, nothing to equip
if (vcdReadBdmaMode() == mode)
return; // the matching variant is already on the card
if (vcdBdmaManualPairPresent())
return; // no marker but a full pair on the card -- manually managed; dumb 1.0.1-style handoff

int er = vcdEquipBdma(source, mode, diag, sizeof(diag));
if (er == 0)
Expand Down