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.

[leo li]

I am using the bluetooth uart module. I wish the new number would replace the old one immediately. But now the number will replace when the old one decreases to 0. I wonder if the NRF52840 module is preemptive or not and how to realize this function.

[awneil]

It's still unclear what your actual problem is:

1. Transferring the new number over BLE to your module?
    
2. In your module firmware, getting access to the new number?
    
3. Writing the new number onto the display?
    
4. Other ... ?

Again, the question of how to write to and update the display has nothing to do with Nordic: the display neither knows nor cares what microcontroller you use - it works the same whatever is driving it.

Therefore, you need to go to the display documentation, and/or the manufacturer, for details of how to control the display.

[Edvin]

When you write a new number it will replace the old number in the service. If the counter isn't updated, then that is because of how you treat it in your application.

The nus_data_handler() is called when you "refresh" the number by sending the number to your characteristic. How you use this number after that is up to the application. I don't know how you use this event, and how you start your countdown, but it sounds like you need to abort the current countdown, and start it again with the new number.

[awneil]

leo li said:

I am using the bluetooth uart module.

You mean the Nordic UART Service (NUS) ?

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.3.0/group__ble__nus.html

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.3.0/ble_sdk_app_nus_eval.html

As Edvin says, that gives you an Event when data is received.

So it's up to your code to do whatever you want when that Event occurs.

[leo li]

Yes, this is exactly what I mean. I want to abort the current countdown and start it with the new number. But I don't know how to realize this function. I just rewrite the nus_data_handler() function with a very easy logic. I changed the receive data into int, and let it decrease. The code is like this:

static void nus_data_handler(ble_nus_evt_t * p_evt)
{
     if (p_evt->type == BLE_NUS_EVT_RX_DATA)
    {
    
        int time_now_s;

        time_now_s=atoi((char*)p_evt->params.rx_data.p_data);
        ...
        ...
        ...
         while(time_now_s>0) 
		 {
            time_now_s--;
            ...
            ...
            ...

And the service_init() function is like this:

static void services_init(void)
{
    uint32_t           err_code;
    ble_nus_init_t     nus_init;
    nrf_ble_qwr_init_t qwr_init = {0};
	//	ble_nus_evt_t *pp_evt;

    // Initialize Queued Write Module.
    qwr_init.error_handler = nrf_qwr_error_handler;

    err_code = nrf_ble_qwr_init(&m_qwr, &qwr_init);
    APP_ERROR_CHECK(err_code);

    // Initialize NUS.
    memset(&nus_init, 0, sizeof(nus_init));
	
	
    nus_init.data_handler = nus_data_handler;
	
    err_code = ble_nus_init(&m_nus, &nus_init);
    APP_ERROR_CHECK(err_code);
}

I don't know whether these code will help you to understand my meanings or not.

Thank you for your continuous attention to my questions.