3 files changed, 14 insertions, 4 deletions
diff --git a/src/common/tusb_fifo.h b/src/common/tusb_fifo.h
index de32e3cfb..005282824 100644
--- a/src/common/tusb_fifo.h
+++ b/src/common/tusb_fifo.h
@@ -244,7 +244,9 @@ TU_ATTR_ALWAYS_INLINE static inline uint16_t tu_fifo_depth(const tu_fifo_t *f) {
 }
 
 TU_ATTR_ALWAYS_INLINE static inline bool tu_fifo_empty(const tu_fifo_t *f) {
-  return f->wr_idx == f->rd_idx;
+  const uint16_t wr_idx = f->wr_idx;
+  const uint16_t rd_idx = f->rd_idx;
+  return wr_idx == rd_idx;
 }
 
 // return number of items in fifo, capped to fifo's depth
diff --git a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
index 381aa0b40..6276f0f07 100644
--- a/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
+++ b/src/portable/st/stm32_fsdev/dcd_stm32_fsdev.c
@@ -293,7 +293,11 @@ static void handle_ctr_tx(uint32_t ep_id) {
       return;
     }
     xfer->iso_in_sending = false;
+#if FSDEV_USE_SBUF_ISO == 0
     uint8_t buf_id = (ep_reg & USB_EP_DTOG_TX) ? 0 : 1;
+#else
+    uint8_t buf_id = BTABLE_BUF_TX;
+#endif
     btable_set_count(ep_id, buf_id, 0);
   }
 
@@ -774,7 +778,12 @@ static bool edpt_xfer(uint8_t rhport, uint8_t ep_num, tusb_dir_t dir) {
 
     uint16_t cnt = tu_min16(xfer->total_len, xfer->max_packet_size);
 
-    if (ep_is_iso(ep_reg)) {
+#if FSDEV_USE_SBUF_ISO == 0
+    bool const dbl_buf = ep_is_iso(ep_reg);
+#else
+    bool const dbl_buf = false;
+#endif
+    if (dbl_buf) {
       btable_set_rx_bufsize(ep_idx, 0, cnt);
       btable_set_rx_bufsize(ep_idx, 1, cnt);
     } else {
diff --git a/src/portable/st/stm32_fsdev/fsdev_stm32.h b/src/portable/st/stm32_fsdev/fsdev_stm32.h
index 30ffadc35..e7a57aca0 100644
--- a/src/portable/st/stm32_fsdev/fsdev_stm32.h
+++ b/src/portable/st/stm32_fsdev/fsdev_stm32.h
@@ -202,8 +202,7 @@
   #include "stm32u0xx.h"
   #define FSDEV_PMA_SIZE (1024u)
   #define FSDEV_BUS_32BIT
-  // Disable SBUF_ISO on U0 for now due to bad performance (audio glitching)
-  #define FSDEV_HAS_SBUF_ISO 0
+  #define FSDEV_HAS_SBUF_ISO 1
   #define USB USB_DRD_FS
 
   #define USB_EP_CTR_RX USB_EP_VTRX