UART break detection failed

RE: UART break detection failed

Jared — Thu, 07 Oct 2021 13:48:48 GMT

Hi,

[quote user="Rainer303"]but write the ERRORSRC register with the fixed value of 0x0C to reset the framing and break bits. [/quote]

The reset value is 0 for the ERRORSRC register. Setting it to 0x0C will set the framing and break bit to present. Could you instead modify the nrf_uarte_errorsrc_get_and_clear() by first checking which bit that is high and then resetting it by writing a 0 to the register?

[quote user="Rainer303"]

The delay of min 70us, which I inserted as a solution gives a timeslot in which the break bit can be set through the hardware in the ERRORSRC register.

[/quote]

Could you elaborate on the necessity for the delay?

regards

Jared

RE: UART break detection failed

Rainer303 — Thu, 07 Oct 2021 07:14:52 GMT

Hello Jared,

thanks for your reply.

[quote userid="73165" url="~/f/nordic-q-a/80312/uart-break-detection-failed/332863#332863"]Not quite, the framing is effectively always generated before a break condition, but the nrf_uarte_errorsrc_get_and_clear() shouldn't clear the break bit in the ERRORSRC register when a framing error has happened. [/quote]

Yes, that shouldn´t happen. But the reading of the ERRORSRC register, triggered through the framing interrupt prevents the setting of the break bit in the ERRORSRC register. Inserting a delay in the function nrf_uarte_errorsrc_get_and_clear() helps a lot, Now I get the break condition event in my uart_rxd_event_handler(). The minimum delay for a reliable break detection is 70us.

__STATIC_INLINE uint32_t nrf_uarte_errorsrc_get_and_clear(NRF_UARTE_Type * p_reg)
{
    nrf_delay_us(70);
    uint32_t errsrc_mask = p_reg->ERRORSRC;
    p_reg->ERRORSRC = errsrc_mask;
    return errsrc_mask;
}

With the knowledge that a break condition will be received, I changed the function nrf_uarte_errorsrc_get_and_clear() for a test case in such a way, that I does not read the ERRORSRC register but write the ERRORSRC register with the fixed value of 0x0C to reset the framing and break bits. This test works fine, I also get the break condition event (twice) in my uart_rxd_event_handler(). With this test it´s obvious, that the reading of the ERRORSRC register triggered through the framing error condition detection prevents the setting of the break bit in the ERRORSRC register.

__STATIC_INLINE uint32_t nrf_uarte_errorsrc_get_and_clear(NRF_UARTE_Type * p_reg)
{
    //nrf_delay_us(70);
    //uint32_t errsrc_mask = p_reg->ERRORSRC;
    uint32_t errsrc_mask = 0x0c;
    p_reg->ERRORSRC = errsrc_mask;
    return errsrc_mask;
}

The delay of min 70us, which I inserted as a solution gives a timeslot in which the break bit can be set through the hardware in the ERRORSRC register.

I would say, there is a hardware problem in the ERRORSRC register handling. A semaphore is missing when the hardware tries to set the break bit and the software simultaneously reads the ERRORSRC register.

Best regards

Rainer

RE: UART break detection failed

Jared — Wed, 06 Oct 2021 14:00:19 GMT

Hi,

[quote userid="108907" url="~/f/nordic-q-a/80312/uart-break-detection-failed"]I read somewhere, that first a framing error is detected and afterwards a break condition is detected when a break condition is received from a peer device. All above means, that the framing interrupt with the following reading of the ERRORSRC register prevents the setting of the break bit in the ERRORSRC register.[/quote]

Not quite, the framing is effectively always generated before a break condition, but the nrf_uarte_errorsrc_get_and_clear() shouldn't clear the break bit in the ERRORSRC register when a framing error has happened.

[quote userid="108907" url="~/f/nordic-q-a/80312/uart-break-detection-failed"]But I never get the break condition, only a few framing error conditions in series. I checked the run-time behavior with a debugger. Setting a breakpoint directly at the beginning of the isr "uarte_irq_handler", and after sending the break condition with the peer device, I can see that both bits, break and framing, in the ERRORSRC register are set.[/quote]

So you can see that the break bit being set in the uarte_irq_handler but not in your uart_rxd_event_handler() which you have added to the serial lib?? Could you post code that shows how you forward the ERRORSRC error to your modified handler?

regards
Jared