From 96f8438ea2b8a06c66fdcd8a4e557224b2c8922a Mon Sep 17 00:00:00 2001
From: MrKevinWeiss <weiss.kevin604@gmail.com>
Date: Fri, 14 Dec 2018 11:08:51 +0100
Subject: [PATCH] cpu/stm32_common/uart: Prevent uart from sending if not
 initialized

Due to the stdio getting called after periph_init the uart may send before initialized.
This adds a simple check so the uart does not get into a locked-up state.
---
 cpu/stm32_common/periph/uart.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/cpu/stm32_common/periph/uart.c b/cpu/stm32_common/periph/uart.c
index 54adaea1d0..76c3d6d595 100644
--- a/cpu/stm32_common/periph/uart.c
+++ b/cpu/stm32_common/periph/uart.c
@@ -145,7 +145,12 @@ static inline void wait_for_tx_complete(uart_t uart)
 void uart_write(uart_t uart, const uint8_t *data, size_t len)
 {
     assert(uart < UART_NUMOF);
-
+#if DEVELHELP
+    /* If tx is not enabled don't try to send */
+    if (!(dev(uart)->CR1 & USART_CR1_TE)) {
+        return;
+    }
+#endif
 #ifdef MODULE_PERIPH_DMA
     if (!len) {
         return;