Not a particularly impressive project, but it was a good learning experience to play around with Linux device tree overlays and the like. Hopefully other people can take some of the lessons from this project as a jumping-off point for using the PRUSS subsystems on the BeagleBone Black.
Temperature input is taken from a DS18B20 one-wire thermometer through the sysfs interface.
The temperature is displayed on a cheap multiplexed common cathode 7-segment display. This display is driven using the AM335x's Programmable Realtime Units to take this logic off of the CPU.
The default pin configuration is for a Knight Lights Dual Digit Display (though mine is labelled incorrectly...), but it can be remapped without having to recompile the driver.
| BBB Pin | P9.31 | P9.29 | P9.30 | P9.28 | P9.42 | P9.27 | P9.41 | P9.25 | P8.12 | P8.11 |
|---|---|---|---|---|---|---|---|---|---|---|
| PRU0 Pin | r30_0 | r30_1 | r30_2 | r30_3 | r30_4 | r30_5 | r30_6 | r30_7 | r30_14 | r30_15 |
| KDD Pin | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
- AM335x_pru_package
- Compiled device tree overlays in /lib/firmware
- Configure the BeagleBone Black using the Device Tree Overlays.
echo W1 > /sys/devices/bone_capemgr.9/slots
echo NJ-PRU-01 > /sys/devices/bone_capemgr.9/slots- run
./thermometer,^Cto quit.
- Derek Molloy's excellent Exploring Beaglebone
- DS18B20 device tree overlay cribbed from BoneBrews.com.