UART21 can't receive RX data

RE: UART21 can't receive RX data

Kazi Afroza Sultana — Tue, 14 Oct 2025 10:51:09 GMT

Can try to use interrupt driven UART instead of async if you need to receive data during sleep?

RE: UART21 can't receive RX data

Kazi Afroza Sultana — Tue, 14 Oct 2025 10:48:40 GMT

Hello,

I can see a previous case (9) [nrf54L15-PDK] Trying to use pin2.07 & pin2.08 with UARTE instance uart21, but get framing error - Nordic Q&A - Nordic DevZone - Nordic DevZone similar to yours.

You can try to call "NRF_POWER->TASKS_LOWPWR = 1;" when UART peripheral is no longer in use.

RE: UART21 can't receive RX data

Metal01 — Tue, 14 Oct 2025 03:24:38 GMT

the init function is:

void hal_app_usart_init(uint32_t baud, hal_app_usart_rx_callback callback)

{

int ret = 0;

if (!device_is_ready(uart))

{

LOG_ERR("UART device not ready");

}

const struct uart_config uart_cfg =

{

.baudrate = baud,

.parity = UART_CFG_PARITY_NONE,

.stop_bits = UART_CFG_STOP_BITS_1,

.data_bits = UART_CFG_DATA_BITS_8,

.flow_ctrl = UART_CFG_FLOW_CTRL_NONE

};

ret = uart_configure(uart, &uart_cfg);

if (ret == -ENOSYS)

{

LOG_ERR("UART configure failed");

}

ret = uart_callback_set(uart, uart_cb, NULL);

if (ret)

{

LOG_ERR("UART callback set failed");

}

the send function is:

void hal_app_usart_data_send(uint8_t const *buf, uint16_t len)

{

int ret;

NRF_POWER->TASKS_CONSTLAT = 1;

ret = uart_tx(uart, buf, len, SYS_FOREVER_MS);

if (ret)

{

LOG_ERR("UART TX failed");

}

else

{

}

the receive function is:

static void uart_cb(const struct device *dev, struct uart_event *evt, void *user_data)

{

switch (evt->type)

{

case UART_RX_RDY:

{

const uint8_t *buf = evt->data.rx.buf + evt->data.rx.offset;

size_t len = evt->data.rx.len;

for (size_t i = 0; i < len; i++)

{

_usart_rx_callback(buf[i]);

}

break;

case UART_RX_DISABLED:

uart_rx_enable(dev, _uart_rx_buffer, sizeof(_uart_rx_buffer), RECEIVE_TIMEOUT);

s_uart_rx_is_enabled = true;

break;

case UART_TX_DONE:

uart_rx_enable(dev, _uart_rx_buffer, sizeof(_uart_rx_buffer), RECEIVE_TIMEOUT);

break;

default:

break;

}

RE: UART21 can't receive RX data

Metal01 — Tue, 14 Oct 2025 03:17:58 GMT

I can use CTS/RTS, the config code is：

&pinctrl {

uart21_default: uart21_default {

group1 {

psels = <NRF_PSEL(UART_RX, 2, 7)>,

<NRF_PSEL(UART_TX, 2, 8)>;

};

uart21_sleep: uart21_sleep {

group1 {

psels = <NRF_PSEL(UART_RX, 2, 7)>,

<NRF_PSEL(UART_TX, 2, 8)>;

low-power-enable;

};

&uart21 {

status = "okay";

pinctrl-0 = <&uart21_default>;

pinctrl-1 = <&uart21_sleep>;

pinctrl-names = "default", "sleep";

current-speed = <115200>;

};

RE: UART21 can't receive RX data

Metal01 — Tue, 14 Oct 2025 03:15:41 GMT

Additionally, I have found that my UART is not used in any thread. If I comment out all the k_msleep calls in another thread and let that thread run continuously, the UART works normally. However, if I keep the k_msleep calls, after the UART sends data, if the slave does not respond immediately, the UART on the nRF54 cannot receive the data and the interrupt is not triggered, even though the data waveform is correct.