example to call tud_init() after freeRTOS kernel is started

add note for usb init when using with RTOS

examples/device/cdc_msc_freertos/src/main.c

@@ -83,7 +83,6 @@ void cdc_task(void* params);
 int main(void)
 {
   board_init();
-  tusb_init();
 
   // soft timer for blinky
   blinky_tm = xTimerCreateStatic(NULL, pdMS_TO_TICKS(BLINK_NOT_MOUNTED), true, NULL, led_blinky_cb, &blinky_tmdef);
@@ -116,6 +115,10 @@ void usb_device_task(void* param)
 {
   (void) param;
 
+  // This should be called after scheduler/kernel is started.
+  // Otherwise it could cause kernel issue since USB IRQ handler does use RTOS queue API.
+  tusb_init();
+
   // RTOS forever loop
   while (1)
   {

examples/device/hid_composite_freertos/src/main.c

@@ -79,7 +79,6 @@ void hid_task(void* params);
 int main(void)
 {
   board_init();
-  tusb_init();
 
   // soft timer for blinky
   blinky_tm = xTimerCreateStatic(NULL, pdMS_TO_TICKS(BLINK_NOT_MOUNTED), true, NULL, led_blinky_cb, &blinky_tmdef);
@@ -112,6 +111,10 @@ void usb_device_task(void* param)
 {
   (void) param;
 
+  // This should be called after scheduler/kernel is started.
+  // Otherwise it could cause kernel issue since USB IRQ handler does use RTOS queue API.
+  tusb_init();
+
   // RTOS forever loop
   while (1)
   {

src/device/usbd.h

@@ -42,6 +42,8 @@
 //--------------------------------------------------------------------+
 
 // Init device stack
+// Note: when using with RTOS, this should be called after scheduler/kernel is started.
+// Otherwise it could cause kernel issue since USB IRQ handler does use RTOS queue API.
 bool tud_init (void);
 
 // Task function should be called in main/rtos loop

src/host/usbh.h

@@ -91,6 +91,9 @@ TU_ATTR_WEAK void tuh_umount_cb(uint8_t dev_addr);
 //--------------------------------------------------------------------+
 // CLASS-USBH & INTERNAL API
 //--------------------------------------------------------------------+
+
+// Note: when using with RTOS, this should be called after scheduler/kernel is started.
+// Otherwise it could cause kernel issue since USB IRQ handler does use RTOS queue API.
 bool usbh_init(void);
 bool usbh_control_xfer (uint8_t dev_addr, tusb_control_request_t* request, uint8_t* data);
 

src/tusb.h

@@ -109,6 +109,8 @@
  *  @{ */
 
 // Initialize device/host stack
+// Note: when using with RTOS, this should be called after scheduler/kernel is started.
+// Otherwise it could cause kernel issue since USB IRQ handler does use RTOS queue API.
 bool tusb_init(void);
 
 // Check if stack is initialized