Merge pull request #9882 from iNavFlight/dzikuvx-h7-gcc13-potential-fix

Potential fix for GCC 13 VCP broken on H7

Author: DzikuVx

src/main/drivers/nvic.h

@@ -26,4 +26,4 @@
     #else
         #define NVIC_PRIORITY_GROUPING NVIC_PriorityGroup_4
     #endif
-#endif
+#endif

src/main/vcp_hal/usbd_cdc_interface.c

@@ -54,6 +54,8 @@
 #include "usbd_cdc_interface.h"
 #include "stdbool.h"
 #include "drivers/time.h"
+#include "drivers/nvic.h"
+#include "build/atomic.h"
 
 /* Private typedef -----------------------------------------------------------*/
 /* Private define ------------------------------------------------------------*/
@@ -366,14 +368,13 @@ uint32_t CDC_Receive_BytesAvailable(void)
 
 uint32_t CDC_Send_FreeBytes(void)
 {
-    /*
-        return the bytes free in the circular buffer
-
-        functionally equivalent to:
-        (APP_Rx_ptr_out > APP_Rx_ptr_in ? APP_Rx_ptr_out - APP_Rx_ptr_in : APP_RX_DATA_SIZE - APP_Rx_ptr_in + APP_Rx_ptr_in)
-        but without the impact of the condition check.
-    */
-    return ((UserTxBufPtrOut - UserTxBufPtrIn) + (-((int)(UserTxBufPtrOut <= UserTxBufPtrIn)) & APP_TX_DATA_SIZE)) - 1;
+    uint32_t freeBytes;
+
+    ATOMIC_BLOCK(NVIC_PRIO_VCP) {
+        freeBytes = ((UserTxBufPtrOut - UserTxBufPtrIn) + (-((int)(UserTxBufPtrOut <= UserTxBufPtrIn)) & APP_TX_DATA_SIZE)) - 1;
+    }
+
+    return freeBytes;
 }
 
 /**