Experiments with SoftwareTimer

code/parasite/src/main.cpp

@@ -42,7 +42,29 @@ void updateAdvertisingData(parasite::BLEAdvertiser* advertiser,
   }
 }
 
-void timer_cb(TimerHandle_t timer_handle) { Serial.println("timer!"); }
+/*
+ * * WARNING *
+ * To get this callback to work, I had to increase the freeRTOS timer stack in
+ * ~/.platformio/packages/framework-arduinoadafruitnrf52/cores/nRF5/freertos/config/FreeRTOSConfig.h
+ * #define configTIMER_TASK_STACK_DEPTH                             (1024)
+ */
+void timer_cb(TimerHandle_t timer_handle) {
+  Serial.println("timer!");
+  digitalToggle(kLED1Pin);
+
+  double battery_voltage = batt_monitor.Read();
+  Serial.printf("Batt voltage: %f\n", battery_voltage);
+
+  parasite::soil_reading_t soil_reading = soil_monitor.Read();
+  Serial.printf("Moisture val: %d, %f%%\n", soil_reading.raw,
+                100 * soil_reading.parcent);
+
+  updateAdvertisingData(&advertiser, soil_reading, battery_voltage);
+  delay(1000);
+  advertiser.Stop();
+
+  // TODO(rbaron): stop PWM; stop everything to save battery.
+}
 
 void setup() {
   Serial.begin(9600);
@@ -55,20 +77,12 @@ void setup() {
   // Enable fast discharge cycle.
   digitalWrite(kDischargeEnablePin, HIGH);
 
-  timer.begin(5000, timer_cb, /*timerID=*/nullptr, /*repeating=*/true);
+  timer.begin(2000, timer_cb, /*timerID=*/nullptr, /*repeating=*/true);
   timer.start();
 
-  // waitForEvent();
-  // suspendLoop();
+  // Suspend the loop task. Under the hood this is a freeRTOS task set up
+  // by the Adafruit_nNRF52_Arduino package.
+  suspendLoop();
 }
 
-void loop() {
-  double battery_voltage = batt_monitor.Read();
-  Serial.printf("Batt voltage: %f\n", battery_voltage);
-
-  parasite::soil_reading_t soil_reading = soil_monitor.Read();
-  Serial.printf("Moisture val: %d, %f%%\n", soil_reading.raw,
-                100 * soil_reading.parcent);
-
-  updateAdvertisingData(&advertiser, soil_reading, battery_voltage);
-}
+void loop() {}

code/playground/blinky/blinky/blinky.ino

@@ -1,14 +1,16 @@
 #include <Arduino.h>
 
-#define kLED1Pin 18
+#define kLED1Pin 28
 
 void setup() {
-  pinMode(LED_RED, OUTPUT);
+  pinMode(kLED1Pin, OUTPUT);
   Serial.begin(9600);
 }
 
+bool on = false;
 void loop() {
   Serial.println("Hello, world");
-  digitalToggle(LED_RED);
-  delay(1000);
+  digitalWrite(kLED1Pin, on ? LOW : HIGH);
+  on = !on;
+  delay(500);
 }

resources.md

@@ -236,6 +236,52 @@ Questions:
 * [Adafruit_nRF52_Arduino issue](https://github.com/adafruit/Adafruit_nRF52_Arduino/issues/165)
   * `delay()` calls waitForEvent?
   * [suspendLoop](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/master/libraries/Bluefruit52Lib/examples/Peripheral/beacon/beacon.ino#L60) can probably save energy when no deep sleep is used.
+  * [More on power consumption](https://github.com/adafruit/Adafruit_nRF52_Arduino/issues/165#issuecomment-407288522). where @hathach mentions that the `delay()` actually uses [`waitForEvent`](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/wiring.c#L84), which itself calls
+* [Loopless / low power examples](https://github.com/adafruit/Adafruit_nRF52_Arduino/pull/262) pull request on Adafruit_nRF52_Arduino
+  * They use the SoftwareTimer, which
 
+* The example in examples/peripheral/rtc is straight-forward: initialize RTC and set up the TICK and COMPARE0 event. The TICK event is triggered on every clock cycle. The COMPARE0 only when the counter reaches a specified value.
+  * It uses the nrf_drv_rtc.h header, which doesn't seem to be included in the Arduino core implementaton
+  * There's a similar one in Arduino called [nrfx/hal/nrf_rtc.h](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/nordic/nrfx/hal/nrf_rtc.h). It seems to use the same call to `nrf_rtc_cc_set` under the hood.
+  * [nrfx](https://github.com/NordicSemiconductor/nrfx) is "a standalone set of drivers for peripherals present in Nordic Semiconductor's SoCs".
+
+* The [RTC driver](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v15.0.0%2Fgroup__nrfx.html) has some interesting functions:
+  * nrfx_rtc_cc_set
+  * nrfx_rtc_tick_disable
+* Interrupt handlers are registered in the NVIC (nested vectored interrupt controller)
+
+*[wolfssl](https://fossies.org/linux/wolfssl/wolfcrypt/src/port/arm/cryptoCell.c) uses the functions I'm thinking of using.
+
+* Reminders:
+  * RTC0 and RTC1 might be in use. Try using RTC2
+  * Initialize the low frequency clock LFCLKSRC
+  * Disable the TICK interrupt
+  * Set up an IRQ (callback) [example from nordic forum](https://devzone.nordicsemi.com/f/nordic-q-a/52923/rtc-interrupt-handler-not-working)
+  * Set up the COMPARE[0] event/interrupt
+  * Disable LFCLKSTARTED interrupt? [link from nordic forum](https://devzone.nordicsemi.com/f/nordic-q-a/70091/early-wake-up-from-power-clock-irq-when-using-rtc-to-wake-up)
+  * FPU (floating point interrupts) also might trigger the interrupt. Important thread from [nordic](https://devzone.nordicsemi.com/f/nordic-q-a/23242/single-float-division-causing-7x-higher-current-draw)
+  * Doesn't work with C++?? [devzone](https://devzone.nordicsemi.com/f/nordic-q-a/13465/nvic-registered-interrupt-doesn-t-work)
+
+## Deep Sleep with SoftwareTimer
+This is a FreeRTOS scheduled task. It seems to work, but by default it wasn't. I had to increase the FreeRTOS timer stack size, as hinted in [this GitHub issue](https://github.com/adafruit/Adafruit_nRF52_Arduino/issues/188)], in ~/.platformio/packages/framework-arduinoadafruitnrf52/cores/nRF5/freertos/config/FreeRTOSConfig.h.
+
+* Issues
+  * nrfx_clock_init is not linked by default in platformio. Is there a more conventional way of using this?
+  * freeRTOS on Adafruit_nRF52_Arduino uses the RTC. [link](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/freertos/config/FreeRTOSConfig.h)
 # Arduino specifics
-* How `main` works by calling `setup` and `loop`. [Link for Adafruit](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/main.cpp#L74), [link for arduino-nrf5](https://github.com/sandeepmistry/arduino-nRF5/blob/master/cores/nRF5/main.cpp#L27). Or: why dropping the `setup` and `loop` doesn't work directly, as they do with ESP32.
+* How `main` works by calling `setup` and `loop`. [Link for Adafruit](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/main.cpp#L74), [link for arduino-nrf5](https://github.com/sandeepmistry/arduino-nRF5/blob/master/cores/nRF5/main.cpp#L27). Or: why dropping the `setup` and `loop` doesn't work directly, as they do with ESP32.
+
+## FreeRTOS
+* [Low Power Support or tickless idle](https://www.freertos.org/low-power-tickless-rtos.html)
+* [Adafruit use of freeRTOS for scheduling the loop() function in Arduino](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/main.cpp#L94)
+* [Adafruit's SoftwareTimer](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/utility/SoftwareTimer.cpp) also uses freeRTOS tasks
+* How/where is freeRTOS implemented for nrf52?
+  * [Adafruit_nRF52_Arduino/cores/nRF5/freertos/](https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/4d703b6f38262775863a16a603c12aa43d249f04/cores/nRF5/freertos)
+* [FreeRTOS support in nordic SDK](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v15.0.0%2Fnrf_freertos_example.html)
+  * examples/blinky_freertos
+  * examples/blinky_rtc_freertos
+
+# Nordic specifics
+* HAL vs. Drivers
+  * [Great answer on nordic forum](https://devzone.nordicsemi.com/f/nordic-q-a/5964/nrf_dvr_xxx-vs-nrf_xxx)
+  * HAL are lower-level. They provide some functions for accessing registers. Drivers are higher level, and usually use the HAL functions. Drivers can be used with or without SoftDevices.