From 319e499b680fb04b15dbd1334aa1e4f5443eadc0 Mon Sep 17 00:00:00 2001
From: John-Mark Gurney <jmg@funkthat.com>
Date: Fri, 23 Apr 2021 18:53:36 -0700
Subject: [PATCH] add fix so that if it's busy we wait and try again...

---
 stm32/usb/usbd_cdc_if.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/stm32/usb/usbd_cdc_if.c b/stm32/usb/usbd_cdc_if.c
index d8f498c..2b390f4 100755
--- a/stm32/usb/usbd_cdc_if.c
+++ b/stm32/usb/usbd_cdc_if.c
@@ -315,7 +315,13 @@ void usb_printf(const char *format, ...)
     va_start(args, format);
     length = vsnprintf((char *)UserTxBufferFS, APP_TX_DATA_SIZE, (char *)format, args);
     va_end(args);
-    CDC_Transmit_FS(UserTxBufferFS, length);
+    for (;;) {
+        if (CDC_Transmit_FS(UserTxBufferFS, length) == USBD_BUSY) {
+            HAL_Delay(1);
+            continue;
+        }
+        break;
+    }
 }
 /* USER CODE END PRIVATE_FUNCTIONS_IMPLEMENTATION */