Merge pull request #20572 from maribu/cpu/msp430/uart_usci

cpu/msp430/periph_uart: Fix uart_write() for USCI peripheral

cpu/msp430/periph/uart_usci.c

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2015 Freie Universität Berlin
+ *               2024 Marian Buschsieweke
  *
  * This file is subject to the terms and conditions of the GNU Lesser
  * General Public License v2.1. See the file LICENSE in the top level
@@ -15,6 +16,7 @@
  * @brief       Low-level UART driver implementation
  *
  * @author      Hauke Petersen <[email protected]>
+ * @author      Marian Buschsieweke <[email protected]>
  *
  * @}
  */
@@ -130,6 +132,11 @@ void uart_write(uart_t uart, const uint8_t *data, size_t len)
         usci->dev->TXBUF = *data++;
     }
 
+    while (usci->dev->STAT & UCBUSY) {
+        /* busy wait for completion, e.g. to avoid losing chars/bits
+         * before releasing the USCI in TX only mode. */
+    }
+
     if (tx_only) {
         msp430_usci_release(usci);
     }