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cpu: nRF52: move clearing of TXRDY flag

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... before writing the data to avoid an infinite loop in case of multiple thread accessing the UART. (#6029)
This commit is contained in:
jfbortolotti 2016-12-06 10:52:27 +01:00 committed by Kaspar Schleiser
parent 364874f7e1
commit b2e79959b1
1 changed files with 12 additions and 2 deletions
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14
cpu/nrf5x_common/periph/uart.c
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@ -140,12 +140,22 @@ void uart_write(uart_t uart, const uint8_t *data, size_t len)
{ {
if (uart == 0) { if (uart == 0) {
for (size_t i = 0; i < len; i++) { 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 */ /* write data into transmit register */
NRF_UART0->TXD = data[i]; NRF_UART0->TXD = data[i];
/* wait for any transmission to be done */ /* wait for any transmission to be done */
while (NRF_UART0->EVENTS_TXDRDY == 0) {} while (NRF_UART0->EVENTS_TXDRDY == 0) {}
/* reset ready flag */
NRF_UART0->EVENTS_TXDRDY = 0;
} }
} }
} }