From 185757ed413fc7bdc65cf494a6079cfed049f98e Mon Sep 17 00:00:00 2001
From: James Smith <{ID}+{username}@users.noreply.github.com>
Date: Sat, 20 Dec 2025 13:27:29 -0700
Subject: [PATCH 1/3] Added tud_vendor_write_clear() which forcefully clears TX
 buffer

---
 examples/device/webusb_serial/src/main.c |  1 +
 src/class/vendor/vendor_device.c         |  6 ++++++
 src/class/vendor/vendor_device.h         |  7 +++++++
 src/common/tusb_fifo.c                   | 16 ++++++++++++++++
 src/common/tusb_fifo.h                   |  1 +
 src/common/tusb_private.h                |  4 ++++
 6 files changed, 35 insertions(+)

diff --git a/examples/device/webusb_serial/src/main.c b/examples/device/webusb_serial/src/main.c
index 50794bdba..155768b76 100644
--- a/examples/device/webusb_serial/src/main.c
+++ b/examples/device/webusb_serial/src/main.c
@@ -196,6 +196,7 @@ bool tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_requ
           tud_vendor_write_str("\r\nWebUSB interface connected\r\n");
           tud_vendor_write_flush();
         } else {
+          tud_vendor_write_clear(); // anything left in the buffer is now thrown out
           blink_interval_ms = BLINK_MOUNTED;
         }
 
diff --git a/src/class/vendor/vendor_device.c b/src/class/vendor/vendor_device.c
index 9972911e0..ced3c0d71 100644
--- a/src/class/vendor/vendor_device.c
+++ b/src/class/vendor/vendor_device.c
@@ -160,6 +160,12 @@ uint32_t tud_vendor_n_write_available(uint8_t idx) {
   vendord_interface_t *p_itf = &_vendord_itf[idx];
   return tu_edpt_stream_write_available(&p_itf->stream.tx);
 }
+
+uint32_t tud_vendor_n_write_clear(uint8_t idx) {
+  TU_VERIFY(idx < CFG_TUD_VENDOR, 0);
+  vendord_interface_t *p_itf = &_vendord_itf[idx];
+  return tu_edpt_stream_count_and_clear(&p_itf->stream.tx);
+}
 #endif
 
 //--------------------------------------------------------------------+
diff --git a/src/class/vendor/vendor_device.h b/src/class/vendor/vendor_device.h
index d59c885d2..878d7aee0 100644
--- a/src/class/vendor/vendor_device.h
+++ b/src/class/vendor/vendor_device.h
@@ -91,6 +91,9 @@ uint32_t tud_vendor_n_write_flush(uint8_t idx);
 
 // Return number of bytes available for writing in TX FIFO
 uint32_t tud_vendor_n_write_available(uint8_t idx);
+
+// Clear the write buffer and return the number of elements cleared
+uint32_t tud_vendor_n_write_clear(uint8_t idx);
 #endif
 
 // Write a null-terminated string to TX FIFO
@@ -148,6 +151,10 @@ TU_ATTR_ALWAYS_INLINE static inline uint32_t tud_vendor_write_flush(void) {
 TU_ATTR_ALWAYS_INLINE static inline uint32_t tud_vendor_write_available(void) {
   return tud_vendor_n_write_available(0);
 }
+
+TU_ATTR_ALWAYS_INLINE static inline uint32_t tud_vendor_write_clear(void) {
+  return tud_vendor_n_write_clear(0);
+}
 #endif
 
 // backward compatible
diff --git a/src/common/tusb_fifo.c b/src/common/tusb_fifo.c
index e97b6ccce..28086be0b 100644
--- a/src/common/tusb_fifo.c
+++ b/src/common/tusb_fifo.c
@@ -95,6 +95,22 @@ void tu_fifo_clear(tu_fifo_t *f) {
   ff_unlock(f->mutex_rd);
 }
 
+// synchronously count then clear fifo, returning the count
+uint16_t tu_fifo_count_and_clear(tu_fifo_t *f) {
+  ff_lock(f->mutex_wr);
+  ff_lock(f->mutex_rd);
+
+  uint16_t cnt = tu_fifo_count(f);
+
+  f->rd_idx = 0;
+  f->wr_idx = 0;
+
+  ff_unlock(f->mutex_wr);
+  ff_unlock(f->mutex_rd);
+
+  return cnt;
+}
+
 // Change the fifo overwritable mode
 void tu_fifo_set_overwritable(tu_fifo_t *f, bool overwritable) {
   if (f->overwritable == overwritable) {
diff --git a/src/common/tusb_fifo.h b/src/common/tusb_fifo.h
index 2e2a0db6f..75eeded01 100644
--- a/src/common/tusb_fifo.h
+++ b/src/common/tusb_fifo.h
@@ -159,6 +159,7 @@ typedef enum {
 bool tu_fifo_config(tu_fifo_t *f, void *buffer, uint16_t depth, uint16_t item_size, bool overwritable);
 void tu_fifo_set_overwritable(tu_fifo_t *f, bool overwritable);
 void tu_fifo_clear(tu_fifo_t *f);
+uint16_t tu_fifo_count_and_clear(tu_fifo_t *f);
 
 #if OSAL_MUTEX_REQUIRED
 TU_ATTR_ALWAYS_INLINE static inline
diff --git a/src/common/tusb_private.h b/src/common/tusb_private.h
index 10e12c2af..0c1709d49 100644
--- a/src/common/tusb_private.h
+++ b/src/common/tusb_private.h
@@ -144,6 +144,10 @@ TU_ATTR_ALWAYS_INLINE static inline void tu_edpt_stream_clear(tu_edpt_stream_t *
   tu_fifo_clear(&s->ff);
 }
 
+TU_ATTR_ALWAYS_INLINE static inline uint16_t tu_edpt_stream_count_and_clear(tu_edpt_stream_t *s) {
+  return tu_fifo_count_and_clear(&s->ff);
+}
+
 TU_ATTR_ALWAYS_INLINE static inline bool tu_edpt_stream_empty(tu_edpt_stream_t *s) {
   return tu_fifo_empty(&s->ff);
 }

From b7463bad87456303c0b68bda120a300b343f45fa Mon Sep 17 00:00:00 2001
From: James Smith <{ID}+{username}@users.noreply.github.com>
Date: Sun, 21 Dec 2025 06:41:57 -0700
Subject: [PATCH 2/3] Removed tu_fifo_count_and_clear

---
 src/class/vendor/vendor_device.c |  4 +++-
 src/common/tusb_fifo.c           | 16 ----------------
 src/common/tusb_fifo.h           |  1 -
 src/common/tusb_private.h        |  4 ----
 4 files changed, 3 insertions(+), 22 deletions(-)

diff --git a/src/class/vendor/vendor_device.c b/src/class/vendor/vendor_device.c
index ced3c0d71..762cbeebc 100644
--- a/src/class/vendor/vendor_device.c
+++ b/src/class/vendor/vendor_device.c
@@ -164,7 +164,9 @@ uint32_t tud_vendor_n_write_available(uint8_t idx) {
 uint32_t tud_vendor_n_write_clear(uint8_t idx) {
   TU_VERIFY(idx < CFG_TUD_VENDOR, 0);
   vendord_interface_t *p_itf = &_vendord_itf[idx];
-  return tu_edpt_stream_count_and_clear(&p_itf->stream.tx);
+  uint32_t cnt = tu_edpt_stream_read_available(&p_itf->stream.tx);
+  tu_edpt_stream_clear(&p_itf->stream.tx);
+  return cnt;
 }
 #endif
 
diff --git a/src/common/tusb_fifo.c b/src/common/tusb_fifo.c
index 28086be0b..e97b6ccce 100644
--- a/src/common/tusb_fifo.c
+++ b/src/common/tusb_fifo.c
@@ -95,22 +95,6 @@ void tu_fifo_clear(tu_fifo_t *f) {
   ff_unlock(f->mutex_rd);
 }
 
-// synchronously count then clear fifo, returning the count
-uint16_t tu_fifo_count_and_clear(tu_fifo_t *f) {
-  ff_lock(f->mutex_wr);
-  ff_lock(f->mutex_rd);
-
-  uint16_t cnt = tu_fifo_count(f);
-
-  f->rd_idx = 0;
-  f->wr_idx = 0;
-
-  ff_unlock(f->mutex_wr);
-  ff_unlock(f->mutex_rd);
-
-  return cnt;
-}
-
 // Change the fifo overwritable mode
 void tu_fifo_set_overwritable(tu_fifo_t *f, bool overwritable) {
   if (f->overwritable == overwritable) {
diff --git a/src/common/tusb_fifo.h b/src/common/tusb_fifo.h
index 75eeded01..2e2a0db6f 100644
--- a/src/common/tusb_fifo.h
+++ b/src/common/tusb_fifo.h
@@ -159,7 +159,6 @@ typedef enum {
 bool tu_fifo_config(tu_fifo_t *f, void *buffer, uint16_t depth, uint16_t item_size, bool overwritable);
 void tu_fifo_set_overwritable(tu_fifo_t *f, bool overwritable);
 void tu_fifo_clear(tu_fifo_t *f);
-uint16_t tu_fifo_count_and_clear(tu_fifo_t *f);
 
 #if OSAL_MUTEX_REQUIRED
 TU_ATTR_ALWAYS_INLINE static inline
diff --git a/src/common/tusb_private.h b/src/common/tusb_private.h
index 0c1709d49..10e12c2af 100644
--- a/src/common/tusb_private.h
+++ b/src/common/tusb_private.h
@@ -144,10 +144,6 @@ TU_ATTR_ALWAYS_INLINE static inline void tu_edpt_stream_clear(tu_edpt_stream_t *
   tu_fifo_clear(&s->ff);
 }
 
-TU_ATTR_ALWAYS_INLINE static inline uint16_t tu_edpt_stream_count_and_clear(tu_edpt_stream_t *s) {
-  return tu_fifo_count_and_clear(&s->ff);
-}
-
 TU_ATTR_ALWAYS_INLINE static inline bool tu_edpt_stream_empty(tu_edpt_stream_t *s) {
   return tu_fifo_empty(&s->ff);
 }

From b53739dee47ae21a21eaa74e9ae6d17d0def32c8 Mon Sep 17 00:00:00 2001
From: James Smith <{ID}+{username}@users.noreply.github.com>
Date: Sun, 21 Dec 2025 09:06:05 -0700
Subject: [PATCH 3/3] Change return of tud_vendor_n_write_clear from uint32_t
 to bool

---
 src/class/vendor/vendor_device.c | 5 ++---
 src/class/vendor/vendor_device.h | 6 +++---
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/class/vendor/vendor_device.c b/src/class/vendor/vendor_device.c
index 762cbeebc..b8e6fec6f 100644
--- a/src/class/vendor/vendor_device.c
+++ b/src/class/vendor/vendor_device.c
@@ -161,12 +161,11 @@ uint32_t tud_vendor_n_write_available(uint8_t idx) {
   return tu_edpt_stream_write_available(&p_itf->stream.tx);
 }
 
-uint32_t tud_vendor_n_write_clear(uint8_t idx) {
+bool tud_vendor_n_write_clear(uint8_t idx) {
   TU_VERIFY(idx < CFG_TUD_VENDOR, 0);
   vendord_interface_t *p_itf = &_vendord_itf[idx];
-  uint32_t cnt = tu_edpt_stream_read_available(&p_itf->stream.tx);
   tu_edpt_stream_clear(&p_itf->stream.tx);
-  return cnt;
+  return true;
 }
 #endif
 
diff --git a/src/class/vendor/vendor_device.h b/src/class/vendor/vendor_device.h
index 878d7aee0..c3de4c49d 100644
--- a/src/class/vendor/vendor_device.h
+++ b/src/class/vendor/vendor_device.h
@@ -92,8 +92,8 @@ uint32_t tud_vendor_n_write_flush(uint8_t idx);
 // Return number of bytes available for writing in TX FIFO
 uint32_t tud_vendor_n_write_available(uint8_t idx);
 
-// Clear the write buffer and return the number of elements cleared
-uint32_t tud_vendor_n_write_clear(uint8_t idx);
+// Clear the transmit FIFO
+bool tud_vendor_n_write_clear(uint8_t idx);
 #endif
 
 // Write a null-terminated string to TX FIFO
@@ -152,7 +152,7 @@ TU_ATTR_ALWAYS_INLINE static inline uint32_t tud_vendor_write_available(void) {
   return tud_vendor_n_write_available(0);
 }
 
-TU_ATTR_ALWAYS_INLINE static inline uint32_t tud_vendor_write_clear(void) {
+TU_ATTR_ALWAYS_INLINE static inline bool tud_vendor_write_clear(void) {
   return tud_vendor_n_write_clear(0);
 }
 #endif