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drivers: mcux_flexcomm: fix character glitches at low power entry

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Character glitches are observed when entering suspend and standby low
power modes.
To fix it, we make sure the `poll_out` API waits for the character
transfer to complete. This is aligned with the uart driver API
description.

Signed-off-by: Axel Le Bourhis <axel.lebourhis@nxp.com>
This commit is contained in:
Axel Le Bourhis 2025-04-29 17:32:09 +02:00 • committed by Benjamin Cabé
commit 0ecaef0053
1 changed files with 13 additions and 2 deletions
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15
drivers/serial/uart_mcux_flexcomm.c
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@ -134,11 +134,22 @@ static void mcux_flexcomm_poll_out(const struct device *dev,
{ {
const struct mcux_flexcomm_config *config = dev->config; const struct mcux_flexcomm_config *config = dev->config;
/* Wait until space is available in TX FIFO */ /* Wait until space is available in TX FIFO, as per API description:
while (!(USART_GetStatusFlags(config->base) & kUSART_TxFifoEmptyFlag)) { * This routine checks if the transmitter is full.
* When the transmitter is not full, it writes a character to the data register.
* It waits and blocks the calling thread otherwise.
*/
while (!(USART_GetStatusFlags(config->base) & kUSART_TxFifoNotFullFlag)) {
} }
USART_WriteByte(config->base, c); USART_WriteByte(config->base, c);
/* Wait for the transfer to complete, as per API description:
* This function is a blocking call. It blocks the calling thread until the character
* is sent.
*/
while (!(USART_GetStatusFlags(config->base) & kUSART_TxFifoEmptyFlag)) {
}
} }
static int mcux_flexcomm_err_check(const struct device *dev) static int mcux_flexcomm_err_check(const struct device *dev)