Setting up timers on STM32 MCUs is quite the daunting task, but again, RUI3 makes this easy and seamless. There are 5 timers available for general use, RAK_TIMER_0 to RAK_TIMER_4. Each can be set up as a periodic task, RAK_TIMER_PERIODIC, or a one-time thing, RAK_TIMER_ONESHOT.
As shown in the docs, setting it up is easy:
void handler(void *data) {
Serial.printf("[%lu]This is the Timer handler function\r\n", millis());
}
void setup() {
Serial.begin(115200);
if (api.system.timer.create(RAK_TIMER_0, (RAK_TIMER_HANDLER)handler, RAK_TIMER_PERIODIC) != true) {
Serial.printf("Creating timer failed.\r\n");
} else if (api.system.timer.start(RAK_TIMER_0, 1000, NULL) != true) {
Serial.printf("Starting timer failed.\r\n");
}
}But showing a string of text is a bit limited, so I went ahead and produced an example that would be slightly more useful. I added 2 sensors, a RAK1901 and a RAK1902, and sample code from the libraries. I set up the LoRa chip to work in P2P mode, and we were good to go.
As you can see in the code, the loop() event is empty – no need to check for the elapsed time and call a function if the minimum delay has passed: the timer does it all. The one thing you have to be careful of is how much time is required for your callback to run: it should not exceed, or even be close to, the periodicity of your timer. In this case, I am reading from two sensors, and, the most time-consuming task, sending by LoRa at a rate optimized for distance, so a couple of seconds are required (sending the LoRa packet takes about 1.4 seconds). And we don't want to flood the airwaves either. For the purpose of this example, I set up the periodicity at 30 seconds, and this will work without breaking, but it should be much longer. You probably don't need to be updated every 30 seconds anyway...
Time elapsed: 30592
Temperature = 23.04°C
Humidity = 61.24%
Pressure = 1010.60 hPa
Sending `T: 23.04; H: 61.24; P: 1010.60`, len 30 via P2P: ok
Tx done!
Time elapsed: 30592
Temperature = 23.17°C
Humidity = 61.08%
Pressure = 1010.59 hPa
Sending `T: 23.17; H: 61.08; P: 1010.59`, len 30 via P2P: ok
Tx done!
Time elapsed: 30592
Temperature = 23.21°C
Humidity = 60.92%
Pressure = 1010.59 hPa
Sending `T: 23.21; H: 60.92; P: 1010.59`, len 30 via P2P: ok
Tx done!
As you can see, even though I requested 30000 ms, I am getting intervals of 30592 ms. Good enough for a sample app, maybe not for a real-life application. This is an issue in older RUI versions, and should be fixed in an upcoming version.