Issue Using Interrupt Driven UART Callback in nRFConnect To Transmit Data

RE: Issue Using Interrupt Driven UART Callback in nRFConnect To Transmit Data

Vidar Berg — Mon, 26 Sep 2022 13:09:13 GMT

Are you able to share a minimal version of your project that will allow me to replicate the issue here? I can make the ticket private if helps.

[quote user="DataMate"]The tx uart should not be disabled here because the data has apparently not yet been sent. [/quote]

I don't understand why it fails when you disable the TX IRQ inside the UART ISR. While the data may not have been transmitted at that point, it has been loaded to the UARTE's DMA buffer.

I have not been able to reproduce the issue on my side either (using SDK v2.1.0). I also tried to look for relevant issues in the Zephyr release notes, but could not seem to find anything.

Not sure if it's worth mentioning or not, but uart_fifo_fill() will transmit up to 'CONFIG_UART_1_NRF_TX_BUFFER_SIZE' bytes in one go (implementation). This means the UART callback is only invoked once when the data to transmit is less than CONFIG_UART_1_NRF_TX_BUFFER_SIZE in length.

[quote user="DataMate"]There I tried polling with uart_irq_tx_complete, but that took over 900 ms for 7 characters at 115200 baud, 1 stop bit, even parity! [/quote]

This function can only be used inside the UART ISR as noted here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/hardware/peripherals/uart.html#c.uart_irq_tx_complete

RE: Issue Using Interrupt Driven UART Callback in nRFConnect To Transmit Data

DataMate — Sun, 25 Sep 2022 09:45:55 GMT

UART pin assignments are correct for the Fanstel board I'm using.

I found the problem. It's in the callback:

if (tx_data_idx == tx_data_length)

{

uart_irq_tx_disable(dev);

tx_data_idx = 0;

k_sem_give(&tx_sem);

}

The tx uart should not be disabled here because the data has apparently not yet been sent. Evidently, the positive return value of uart_fifo_fill only indicates the number of characters that have been successfully written to the tx fifo, not the number successfully transmitted. Consequently, I need to first wait until the transfer is complete before disabling the tx uart, but this should not be done in the interrupt service routine callback which could block subsequent interrupts, so I removed uart_irq_tx_disable from that conditional block and placed it after k_sem_take in uart_irq_tx. There I tried polling with uart_irq_tx_complete, but that took over 900 ms for 7 characters at 115200 baud, 1 stop bit, even parity! That prevented me from getting a response from the receiver via the uart (not shown here in the code) in time. Do you know why that function takes so long? If I simply use a k_usleep of 500 us, I receive the response, but I'd rather use uart_irq_tx_complete which seems to be intended for that purpose.

RE: Issue Using Interrupt Driven UART Callback in nRFConnect To Transmit Data

Vidar Berg — Thu, 22 Sep 2022 13:53:40 GMT

Hello,

Could you please try to double check the UART pin assignments to make sure they match your board? I tried to use your code with SDK 2.1.0, but did not manage to reproduce the problem.

Test project:

devzone.nordicsemi.com/.../7635.interrupt_5F00_uart_5F00_sdk2.1.0.zip

Log output:

*** Booting Zephyr OS build v3.1.99-ncs1 ***
Test message
UART data transmitted
TX length 14
Hello World! nrf52840dk_nrf52840

Best regards,

Vidar