From b2e79959b188a40de39f0cd7daac0c5fe162acef Mon Sep 17 00:00:00 2001
From: jfbortolotti <jfbortolotti@gmail.com>
Date: Tue, 6 Dec 2016 10:52:27 +0100
Subject: [PATCH] cpu: nRF52: move clearing of TXRDY flag
... before writing the data to avoid an infinite loop in case of multiple thread accessing the UART. (#6029)
---
cpu/nrf5x_common/periph/uart.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/cpu/nrf5x_common/periph/uart.c b/cpu/nrf5x_common/periph/uart.c
index fa6b6f5582..7b90cad4d7 100644
--- a/cpu/nrf5x_common/periph/uart.c
+++ b/cpu/nrf5x_common/periph/uart.c
@@ -140,12 +140,22 @@ void uart_write(uart_t uart, const uint8_t *data, size_t len)
{
if (uart == 0) {
for (size_t i = 0; i < len; i++) {
+ /* This section of the function is not thread safe:
+ - another thread may mess up with the uart at the same time.
+ In order to avoid an infinite loop in the interrupted thread,
+ the TXRDY flag must be cleared before writing the data to be
+ sent and not after. This way, the higher priority thread will
+ exit this function with the TXRDY flag set, then the interrupted
+ thread may have not transmitted his data but will still exit the
+ while loop.
+ */
+
+ /* reset ready flag */
+ NRF_UART0->EVENTS_TXDRDY = 0;
/* write data into transmit register */
NRF_UART0->TXD = data[i];
/* wait for any transmission to be done */
while (NRF_UART0->EVENTS_TXDRDY == 0) {}
- /* reset ready flag */
- NRF_UART0->EVENTS_TXDRDY = 0;
}
}
}
--
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