I am using the NRF2840 and WaveShare's 2.9 epaper display to make a cutdown tool, but I am facing some problems.

[leo li]

I have realized the cutdown function with the examples. But now I want to reflesh the number I have published, which means that I first publish a number, then I want to publish a new number. But now, the new number i published can't preemptive the old number. I want to know how to replace the old number. Thanks for all of your effort.

yours sincerely,

Leo Li.

[Edvin]

I don't know your setup Leo, but if the issue is that the numbers are stacked on top of each other, it sounds like you need to clear the screen first. How you do that, I don't know, but it is probably documented somewhere around the same place as you found out how to write to the epaper display.

[leo li]

Thank you for your reply. I am sorry that I don't describe my question very clearly. I have update my question in the previous answers by awneil. You can go to that answer to know further things. Thank you very much.

[awneil]

leo li said:

I just can't abort the countdown

Why not?

What's the problem?

leo li said:

maybe it's because of that the Nordic UART Service is FIFO

Why would that be a problem?

It's your code that does the countdown - so you should know how to abort it!

Can you get this working on its own - without the added complication of BLE?

It sounds like a problem with your system design ...

[Edvin]

Ok, I see.

The issue is that you are handling your entire countdown in the nus_data_handler(). Hence, when a new number enters, it is not able to handle that callback until you finish the handler that you are in now. They are two equal events with the same priority, so the new number is not called until the previous has returned.

I suggest you do something like this:

volatile uint32_t time_now_s = 0;       // remember to use volatile
volatile bool start_countdown = false;  // remember to use volatile
static void nus_data_handler(...)
{
    if (p_evt->type == BLE_NUS_EVT_RX_DATA)
    {
        time_now_s = atoi((char*)p_evt->params.rx_...;
        start_countdown = true;
    }
}

static void start_my_countdown()
{
    while(time_now_s > 0)
    {
        time_now_s--;
        ...
    }
}

main()
{
    ...
    for(;;)
    {
        if(start_countdown)
        {
            start_my_countdown();
            start_countdown = false;
        }
    }
}

But that is also not perfect. You should really use a timer that has a timeout of 1 second or whatever resolution you need, and use the timeout handler to decrement time_now_s and update the display. This way, you will allow the nRF to go to sleep to save some power while you are running the countdown as well.

[leo li]

That's exactly what I mean. I solved the problem with your help. Thank you very much for your kindly help these days.

[leo li]

It's indeed the problem of my design. But I have solved that problem with Edvin's help. Thank you very much for your insistent attention to my problem.

[awneil]

You're welcome.

If the issue is now resolved, please verify the answer: