Unexpected warning

[Malcolm]

I am receiving an unexpected warning from nrf_atfifo_item_get that reports "Get failed - no item in the FIFO." This occurs when I start advertising using

void advertising_start(bool erase_bonds)

This calls bsp_led_indication which calls app_timer_start which triggers drv_rtc_irq_trigger

I am assuming this is to catch short timer periods, but can this warning be avoided so that there is no call to the rtc trigger?

[Jared]

Hi,

I'm not really sure if the error is due to the function call to app_timer_start(). Set a breakpoint where the log is printed, and share the call stack from debug view.

The error is returned if you try to retrieve a char from the FIFO when it's empty.

Are you using an example from the SDK, which one?

regards

Jared 

[Malcolm]

I have started from an example but the code is substantially modified. Here is the call stack

nrf_atfifo_item_get
timer_req_process
rtc_irq
RTC1_IRQHandler
<Exception frame>
drv_rtc_irq_trigger
timer_request_proc_trigger
timer_req_schedule
app_timer_start
application_timers_start
ble_device_init
main
[_call_main + 0xd]

I have a similar issue in bsp_button. When a button is pressed it calls a timer, which never calls the timeout routine. It appears nothing is put in the timer queue.

[Malcolm]

I cannot follow this code:

app_timer_start places a request on the atfifo stack to start a timer. It then requests the timer to do an interrupt that then enacts the request that has been placed on the atfifo stack. So far so good, even if I do not follow the reasoning.

However in the code for timer_req_process I see the line req = nrf_atfifo_item_check(m_req_fifo, &fifo_ctx);, which calls the routine with the address of a variable on the stack that is so far not initialised.

/**
 * @brief Function for processing user requests.
 *
 * Function is called only in the context of RTC interrupt.
 */
static void timer_req_process(drv_rtc_t const * const  p_instance)
{
    nrf_atfifo_item_get_t fifo_ctx;
    timer_req_t *         p_req;
    bool                                    req = nrf_atfifo_item_check(m_req_fifo, &fifo_ctx);

And then in nrf_atfifo_item_check the address of an element in fifo_ctx is passed to another routine. As fifo_ctx is uninitialised it will pass rubbish to the nrf_atfifo_rspace_req routine as the address of last_head.

void * nrf_atfifo_item_get(nrf_atfifo_t * const p_fifo, nrf_atfifo_item_get_t * p_context)
{
    if (nrf_atfifo_rspace_req(p_fifo, &(p_context->last_head)))
    {
 

[Malcolm]

Apologies It appears there is something else going on.

nrf_atfifo_item_check calls nrf_atfifo_rspace_req the first time and reports there is something in the fifo, but in the second call it reports there is nothing in the fifo.

[Malcolm]

Got it. This version of app_timer2 uses nrf_atfifo_item_check to control the loop, but by using nrf_atfifo_rspace_req it removes the item so preventing getting an item from the fifo.

static void timer_req_process(drv_rtc_t const * const  p_instance)
{
    nrf_atfifo_item_get_t fifo_ctx;
    timer_req_t *         p_req;
        bool                                    req = nrf_atfifo_item_check(m_req_fifo, &fifo_ctx);

    while (req)
    {
                p_req = nrf_atfifo_item_get(m_req_fifo, &fifo_ctx);
        switch (p_req->type)
        {

Other versions of timer_req_process do not check and use the call to nrf_atfifo_item_get and its return to control the loop, but this generates a warning on any check.

/**
 * @brief Function for processing user requests.
 *
 * Function is called only in the context of RTC interrupt.
 */
static void timer_req_process(drv_rtc_t const * const  p_instance)
{
    nrf_atfifo_item_get_t fifo_ctx;
    timer_req_t *         p_req = nrf_atfifo_item_get(m_req_fifo, &fifo_ctx);

    while (p_req)
    {
        switch (p_req->type)

It appears nrf_atfifo_item_check needs to be corrected so that it does not remove the item from the fifo