fix(legacy): prevent handling RebootToBootloader recursing by flushing USB write

legacy/firmware/.changelog.d/1985.fixed

@@ -0,0 +1 @@
+Prevent recursing in handling RebootToBootloader by USB flush.

legacy/firmware/fsm.c

@@ -360,8 +360,7 @@ void fsm_msgRebootToBootloader(void) {
   oledRefresh();
   fsm_sendSuccess(_("Rebooting"));
   // make sure the outgoing message is sent
-  usbPoll();
-  usbSleep(500);
+  usbFlush(500);
 #if !EMULATOR
   svc_reboot_to_bootloader();
 #else

legacy/firmware/udp.c

@@ -70,3 +70,5 @@ char usbTiny(char set) {
   tiny = set;
   return old;
 }
+
+void usbFlush(uint32_t millis) { usbSleep(millis); }

legacy/firmware/usb.c

@@ -457,3 +457,23 @@ void usbSleep(uint32_t millis) {
     }
   }
 }
+
+void usbFlush(uint32_t millis) {
+  if (usbd_dev == NULL) {
+    return;
+  }
+
+  static const uint8_t *data;
+  data = msg_out_data();
+  if (data) {
+    while (usbd_ep_write_packet(usbd_dev, ENDPOINT_ADDRESS_MAIN_IN, data,
+                                USB_PACKET_SIZE) != USB_PACKET_SIZE) {
+    }
+  }
+
+  uint32_t start = timer_ms();
+
+  while ((timer_ms() - start) < millis) {
+    asm("nop");
+  }
+}

legacy/firmware/usb.h

@@ -27,5 +27,6 @@ void usbPoll(void);
 void usbReconnect(void);
 char usbTiny(char set);
 void usbSleep(uint32_t millis);
+void usbFlush(uint32_t millis);
 
 #endif