arduino-pico-sleep

Example sketch for using sleep mode (wake-up by RTC) with Arduino Pico RP2040

This example allows to implement a sleep function similar to the ESP32's. See the differences below:

No.	Topic	ESP32	RP2040
1	Wake-up criterion	Sleep duration	Wake-up date & time
2	Wake-up behaviour	Restart sketch	Continue sketch
3	RTC reset by restart	No	Yes
4	Retain data during sleep mode	RTC RAM	Yes
5	Retain data during restart	RTC RAM	a) Watchdog scratch registers b) uninitialized RAM section 1

1. see rp2_common/pico_platform/include/pico/platform.h: Section attribute macro for data that is to be left uninitialized

RP2040 Workarounds/Solutions

1. Create date and time from epoch, set HW RTC Instead of using struct tm, datetime_t has to be used for this.

2. If the sketch needs to be restartet after wake-up, rp2040.restart() has to be called.

3. A restart resets the RTC. This is a problem if you are using the RTC for providing time and date.

4. The RP2040 retains all data during sleep mode - nothing to be done here.

5. If you only have to keep a few bytes during restart, you can use the watchdog scratch registers. Please note that the bootloader used a few of them too. In the example, the epoch time (variable time_saved) and a few application variables are retained this way.

RTC Setting / Resynchronization

In an embedded device, you would normally use

• Internet (NTP)
• A radio clock signal
• GPS
• LoRaWAN as the time source for setting the RTC.

In this example, the user is requested to enter date/time via serial console.

Embedded RTCs (or more precisely: their crystal oscillators) tend to have certain inaccuracies which accumulate over time. Therefore it is often desired to resynchronize the RTC to the time source after a certain time (CLOCK_SYNC_INTERVAL). For this purpose, the variable rtcLastClockSync is used to keep the timestamp of the last synchronization.

Extras

In some cases, it is useful to align the wake-up time to the wall clock time, e.g. at 5, 10, 15 minutes etc. after the full hour. This should even work with varying run-time after wake-up. The example provides this, too.

Notes

General

• https://www.raspberrypi.com/documentation/microcontrollers/rp2040.html
• https://datasheets.raspberrypi.com/rp2040/rp2040-product-brief.pdf
• https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf
• https://github.com/raspberrypi/pico-sdk
• https://github.com/earlephilhower/arduino-pico
• https://arduino-pico.readthedocs.io/en/latest/index.html

Adafruit Feather RP2040

• https://www.adafruit.com/product/4884
• https://learn.adafruit.com/adafruit-feather-rp2040-pico/

Sleep Mode

• Power-saving possibilities using the arduino-pico core earlephilhower/arduino-pico#1544 (comment)
  • https://github.com/lyusupov/SoftRF/tree/master/software/firmware/source/libraries/RP2040_Sleep
    • https://github.com/raspberrypi/pico-extras/blob/master/src/rp2_common/pico_sleep/sleep.c
    • https://github.com/raspberrypi/pico-extras/blob/master/src/rp2_common/pico_sleep/include/pico/sleep.h
    • https://github.com/raspberrypi/pico-extras/blob/master/src/rp2_common/hardware_rosc/rosc.c
    • https://github.com/raspberrypi/pico-extras/blob/master/src/rp2_common/hardware_rosc/include/hardware/rosc.h
• earlephilhower/arduino-pico#345
• https://www.heise.de/blog/Sleepy-Pico-ein-Raspberry-Pi-Pico-geht-mit-C-C-schlafen-6046517.html
• Software Reset: https://forums.raspberrypi.com/viewtopic.php?t=318747
• https://github.com/raspberrypi/pico-extras/blob/master/src/rp2_common/pico_sleep/sleep.c
• void rp2040.reboot() https://github.com/earlephilhower/arduino-pico/blob/master/docs/rp2040.rst#void-rp2040reboot
• RP2040 ultra low power wake on RTC: https://forums.raspberrypi.com/viewtopic.php?t=338245
• https://ghubcoder.github.io/posts/awaking-the-pico/

Resets

• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2_common/hardware_resets/include/hardware/resets.h
• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2040/hardware_regs/include/hardware/regs/resets.h
• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2040/hardware_structs/include/hardware/structs/vreg_and_chip_reset.h
• Arduino Nano RP2040 Connect - determine reason for reset / read rp2040 chip_reset register - SOLVED - Nano Family / Nano RP2040 Connect - Arduino Forum
• restart()/reboot():
  • ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/cores/rp2040/RP2040Support.h
  • ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2_common/hardware_watchdog/watchdog.c
  • bool watchdog_caused_reboot(void);
    • ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2_common/hardware_watchdog/include/hardware/watchdog.h

RTC

• https://www.raspberrypi.com/documentation/pico-sdk/hardware.html#hardware_rtc
• Setting/getting RTC time https://github.com/raspberrypi/pico-examples/blob/master/rtc/hello_rtc/hello_rtc.c
• ESP32Time:
  • rtc.setTime(time_t)
  • time_t rtc.getLocalEpoch()
• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2040/hardware_structs/include/hardware/structs/rtc.h
• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2040/hardware_regs/include/hardware/regs/rtc.h
• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/pico-sdk/src/rp2_common/hardware_rtc/rtc.c
• https://community.element14.com/products/arduino/b/blog/posts/real-time-clock-on-the-raspberry-pi-pico
• ~/.arduino15/packages/rp2040/hardware/rp2040/3.6.0/libraries/rp2040/examples/Time/Time.ino
• Is the RTC nearly useless or is it me? https://forums.raspberrypi.com/viewtopic.php?t=325598#p1950784
• no separate RTC XTAL on Adafruit Feather RP2040
• Using Timezones/Local Time on the Pico https://forums.raspberrypi.com/viewtopic.php?t=350488