BLE ANT App Timer

[Alex]

Hi all,

I have a firmware in which I want to use BLE and ANT communication (with Softdevice S310) to send and receive commands from other Nordic devices or smartphones. I also have 64 RGB LEDs WS2812 which have a specific communication protocol and I want to update the color of the LEDs at a given frequency. I plan to do that by instantiating an App Timer as described here.

It is important that the communication to the LEDs is not interrupted by any events or interrupts.

So I have BLE & ANT events as well as a timer handler.

What is the best way to handle this? It is important that the communication to the LEDs is not interrupted and that I can still communicate through BLE and ANT from time to time.

One possibility would be to setup a radio notification with ble_radio_notification_init(NRF_APP_PRIORITY_HIGH, NRF_RADIO_NOTIFICATION_DISTANCE_2680US,myradio_callback_handler); to know when the radio is active. Then I could set a flag each time I enter my Timeout handler to request for an update of the LEDs color. In the main loop, I could just check these two conditions to be active at the same time and then update the LEDs.

Is there a better way to do this? Would a Scheduler or a TImeslot API be more appropriate?

Best regards

[Anders Strand]

Hello.

In the WS2812 data sheet, we can see that the shortest pulse we must send is 0.35 uS. The lowest time we can count with the app_timer is 32 uS, because it uses the 32khz RTC timer.

You can find a library for using ws2812 with the nRF51 on this github page. This implementation bit-bangs the protocol using assembly. This is the most common way of interfacing to the ws2812 (afaik). They also included a note about using the lib with a softdevice. As you suggested, it uses the radio notification API.

Sending data to one led will take about 32 uS. Since it is so fast, it is ok to just do a blocking implementation (bit banging). Just do it right after the radio events are finished.

The timeslot API could also be used, but you would not be guaranteed a slot 100% periodically.

-Anders

[Alex]

I have 64 LEDs to update. That makes 64 * 32us = 2048us Is that ok to update the LEDs in the timer event handler itself? I thought that it was good practice to have few instructions executed in a short amount of time in the event handlers in general...