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Raspberry Pi watchdog updates and serial console notes #30

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20 changes: 14 additions & 6 deletions Raspberry_Pi.md
Original file line number Diff line number Diff line change
@@ -166,14 +166,16 @@ Where `<id>` is:

### Watchdog
BCM2708 has a hardware watchdog which can be utilized by enabling the
`bcm2708_wdog` kernel module.
`bcm2708_wdog` kernel module, `bcm2709_wdog` for the Pi 2, or `bcm2835_wdt`
for the Pi 3. In most cases these modules will load automatically.

For proper operation the watchdog daemon also has to be installed, configured
(by uncommenting the "watchdog-device" line in `/etc/watchdog.conf`) and
enabled.
To activate the watchdog, set the `RuntimeWatchdogSec` value in
`/etc/systemd/system.conf`. The largest permitted value is `15s` due to
hardware limitations.

This should also apply for Raspberry Pi 2 by using the `bcm2709_wdog` module
and Raspberry Pi 3 by using the `bcm2835_wdt` module.
The watchdog service is part of systemd, so no further configuration needs to
be done. `/etc/watchdog.conf` is no longer required as it was in the past, and
separate `systemctl` steps to enable and activate the service no longer apply.

## Hardware Random Number Generator
Arch Linux ARM for the Raspberry Pi had the `bcm2708-rng` module set to load at
@@ -258,6 +260,12 @@ To use the GPIO/SPI pins as a regular non-root user (in group `tty`), add the fo
SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:tty /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add", PROGRAM="/bin/sh -c 'chown root:tty /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"

### Serial Console

Adding `console=ttyAMA0,115200` to the kernel command line will enable it from
the kernel's perspective. On some models, the serial UART conflicts with the
Bluetooth UART, so disabling Bluetooth with `dtoverlay=disable-bt` in
`config.txt` may be required in order to get the serial console working.

## See Also