3 files changed, 21 insertions, 0 deletions
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);
 }