libuarte sometimes print garbled

RE: libuarte sometimes print garbled

leo.lau — Tue, 26 Jan 2021 06:36:59 GMT

Thank you for your suggestion.

RE: libuarte sometimes print garbled

Krzysztof Chruscinski — Wed, 16 Dec 2020 15:53:18 GMT

Hi,

unfortunately, libuarte is currently not thread safe. It is returning NRF_ERROR_BUSY when transfer is in progress but setting busy state is done without protection so there is a chance for race. It can be easily fixed in `nrf_libuarte_drv.c`

In the beginning of nrf_libuarte_drv_tx() function there is

    if (p_libuarte->ctrl_blk->p_tx)
    {
        return NRF_ERROR_BUSY;
    }
    p_libuarte->ctrl_blk->p_tx = p_data;

That can be replaced with:

if (!nrf_atomic_u32_cmp_exch(&p_libuarte->ctrl_blk->p_tx, NULL, p_data)) {
  return NRF_ERROR_BUSY;
}

Code above is using exclusive access to safely set p_tx which is used for determining if driver is busy. That will make it thread safe.

Regarding nrf_queue, it is thread safe.

If you don't want to modify libuarte code you would need to wrap tx call with critical region.

Krzysztof

RE: libuarte sometimes print garbled

leo.lau — Thu, 26 Nov 2020 08:12:49 GMT

Thank you for your response. I have solved the problem that there is a bug in my code.

I'm sorry to bother you.

On the other hand, I have few questions about libuarte and ble_app_multilink.

1. Is libuarte thread-safe? What happens if two peripheral's events calling nrf_libuarte_async_tx.

2. Is nrf_queue thread-safe? I know nrf_queue is interrupt secure. Is that equals to thread-safe?

3. Is the following code looks good for two peripherals?

buffer_t buf;
buf.p_data = p_lbs_c_evt->params.button.p_data;
buf.length = (uint8_t)p_lbs_c_evt->params.button.data_len;

ret_code_t err_code = nrf_libuarte_async_tx(&libuarte, buf.p_data, buf.length);
if (err_code == NRF_ERROR_BUSY){
    if (!nrf_queue_is_full(&m_buf_queue)){
        ret_code_t err_code = nrf_queue_push(&m_buf_queue, &buf);
        APP_ERROR_CHECK(err_code);
    }
}

4. If libuarte/nrf_queue not thread-safe, should I need to implement something like

CRITICAL_REGION_ENTER();

CRITICAL_REGION_EXIT();

Best Regards

Leo

RE: libuarte sometimes print garbled

Jørgen Holmefjord — Wed, 25 Nov 2020 13:27:17 GMT

Hi,

RTT works over SWD, and should not interfere with the UART interface. Could it be some issue with the buffer scopes, causing the libUARTE buffers to be overwritten before being processed/transmitted?

Have you tested with different UART pins, just to make sure there is nothing else in the application trying to write to these pins?

Best regards,
Jørgen