RTCreboot

Rebooting the PI using the wake-on-alarm function of the MCP7940N

This example uses two programs:

• rtcreboot which sets the alarm a number of seconds in the future and then shuts down the RPi. The default is 120 seconds. You can specify a different delay (in seconds) as an argument to rtcreboot. rtcreboot writes the expected reboot time on the Papirus display.

• the second program is bootinfo which should be run at system boot. This writes the start time (the output from uptime -s, the current system time and the hardware clock time (normally in UTC) to the Papirus display.

Both programs rely on the smbusf module (See py_smbusf for build and installation instructions). In order to run bootinfo at system boot add the following line to /etc/rc.local:

sudo -u pi python /home/pi/PaPiRus/RTC-Hat-Examples/RTCreboot/bootinfo

Modify the path as required for your installation.
bootinfo has to be run as user pi, since the smbusf module is only installed for user pi when you follow the instructions in py_smbusf.

Both programs use support functions in prtc.py (hardware clock access functions) and pwrite_text.py (custom version to write text on the Papirus display)

The programs text output is layed out for the large Papirus display (2.7 inch 264 x 176).

For the programming details of the MCP7940N the datasheet is the best reference. See section 5 and especially section 5.4 about alarms.