dcd(fsdev): don't disarm an armed endpoint on clear-halt toggle reset

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HeF2gZ1M7GWkz6Av4BpKPg

1 files changed, 11 insertions, 1 deletions

diff --git a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
index aecd689b3..ba05818b6 100644
--- a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
+++ b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
@@ -835,7 +835,17 @@ void dcd_edpt_clear_stall(uint8_t rhport, uint8_t ep_addr) {
   ep_reg &= U_EPREG_MASK | EP_STAT_MASK(dir) | EP_DTOG_MASK(dir);
 
   if (!ep_is_iso(ep_reg)) {
-    ep_change_status(&ep_reg, dir, EP_STAT_NAK);
+    // Only knock a genuinely STALLED endpoint down to NAK (the class then re-arms it). If the
+    // endpoint is armed (VALID) - e.g. a clear-halt used purely to reset the data toggle, as in
+    // usbtest case 29 - leave STAT untouched so the in-flight transfer isn't disarmed with no
+    // completion, which would leak the usbd claim and starve the endpoint. Masking the STAT bits
+    // to 0 writes no toggle, so an armed/idle endpoint keeps its current status.
+    const uint8_t stat_pos = (uint8_t) (U_EPTX_STAT_Pos + (dir == TUSB_DIR_IN ? 0u : 8u));
+    if (((ep_reg >> stat_pos) & 0x3u) == EP_STAT_STALL) {
+      ep_change_status(&ep_reg, dir, EP_STAT_NAK);
+    } else {
+      ep_reg &= ~EP_STAT_MASK(dir);
+    }
   }
   ep_change_dtog(&ep_reg, dir, 0); // Reset to DATA0
   ep_write(ep_idx, ep_reg, true);