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

Question

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 · Accepted Answer

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.

awneil · Answer

leo li said: the number I have published 
 What do you mean by " published " here? 
 leo li said: the new number i published can't preemptive the old number 
 What do you mean by that? 
 leo li said: I want to know how to replace the old number. 
 You mean, how to update the display? 
 That has nothing to do with Nordic - you need to contact the display manufacturer (WaveShare?) for that.

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

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