3 files changed, 19 insertions, 11 deletions
diff --git a/src/device/dcd.h b/src/device/dcd.h
index 8d042bbde..d43a0dd9a 100644
--- a/src/device/dcd.h
+++ b/src/device/dcd.h
@@ -153,7 +153,7 @@ bool dcd_edpt_xfer            (uint8_t rhport, uint8_t ep_addr, uint8_t * buffer
 // This API is optional, may be useful for register-based for transferring data.
 bool dcd_edpt_xfer_fifo       (uint8_t rhport, uint8_t ep_addr, tu_fifo_t * ff, uint16_t total_bytes) TU_ATTR_WEAK;
 
-// Stall endpoint
+// Stall endpoint, any queuing transfer should be removed from endpoint
 void dcd_edpt_stall           (uint8_t rhport, uint8_t ep_addr);
 
 // clear stall, data toggle is also reset to DATA0
diff --git a/src/device/usbd.c b/src/device/usbd.c
index 7cd8fad42..a52ea9afe 100644
--- a/src/device/usbd.c
+++ b/src/device/usbd.c
@@ -1333,26 +1333,33 @@ bool usbd_edpt_busy(uint8_t rhport, uint8_t ep_addr)
 
 void usbd_edpt_stall(uint8_t rhport, uint8_t ep_addr)
 {
-  TU_LOG(USBD_DBG, "    Stall EP %02X\r\n", ep_addr);
 
   uint8_t const epnum = tu_edpt_number(ep_addr);
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
-  dcd_edpt_stall(rhport, ep_addr);
-  _usbd_dev.ep_status[epnum][dir].stalled = true;
-  _usbd_dev.ep_status[epnum][dir].busy = true;
+  // only stalled if currently cleared
+  if ( !_usbd_dev.ep_status[epnum][dir].stalled )
+  {
+    TU_LOG(USBD_DBG, "    Stall EP %02X\r\n", ep_addr);
+    dcd_edpt_stall(rhport, ep_addr);
+    _usbd_dev.ep_status[epnum][dir].stalled = true;
+    _usbd_dev.ep_status[epnum][dir].busy = true;
+  }
 }
 
 void usbd_edpt_clear_stall(uint8_t rhport, uint8_t ep_addr)
 {
-  TU_LOG(USBD_DBG, "    Clear Stall EP %02X\r\n", ep_addr);
-
   uint8_t const epnum = tu_edpt_number(ep_addr);
   uint8_t const dir   = tu_edpt_dir(ep_addr);
 
-  dcd_edpt_clear_stall(rhport, ep_addr);
-  _usbd_dev.ep_status[epnum][dir].stalled = false;
-  _usbd_dev.ep_status[epnum][dir].busy = false;
+  // only clear if currently stalled
+  if ( _usbd_dev.ep_status[epnum][dir].stalled )
+  {
+    TU_LOG(USBD_DBG, "    Clear Stall EP %02X\r\n", ep_addr);
+    dcd_edpt_clear_stall(rhport, ep_addr);
+    _usbd_dev.ep_status[epnum][dir].stalled = false;
+    _usbd_dev.ep_status[epnum][dir].busy = false;
+  }
 }
 
 bool usbd_edpt_stalled(uint8_t rhport, uint8_t ep_addr)
diff --git a/src/device/usbd_pvt.h b/src/device/usbd_pvt.h
index 6a4b30956..7607b9895 100644
--- a/src/device/usbd_pvt.h
+++ b/src/device/usbd_pvt.h
@@ -81,7 +81,7 @@ bool usbd_edpt_claim(uint8_t rhport, uint8_t ep_addr);
 // Release an endpoint without submitting a transfer
 bool usbd_edpt_release(uint8_t rhport, uint8_t ep_addr);
 
-// Check if endpoint transferring is complete
+// Check if endpoint is busy transferring
 bool usbd_edpt_busy(uint8_t rhport, uint8_t ep_addr);
 
 // Stall endpoint
@@ -93,6 +93,7 @@ void usbd_edpt_clear_stall(uint8_t rhport, uint8_t ep_addr);
 // Check if endpoint is stalled
 bool usbd_edpt_stalled(uint8_t rhport, uint8_t ep_addr);
 
+// Check if endpoint is ready (not busy and not stalled)
 TU_ATTR_ALWAYS_INLINE static inline
 bool usbd_edpt_ready(uint8_t rhport, uint8_t ep_addr)
 {