hc-sr04-range-sensor

This is yet another HC-SR04 range sensor example for PRU. In an attempt to differentiate, it was written for the shiny new remoteproc/rpmsg driver, instead of the old uio_pruss.

To understand the rpmsg code here please visit http://processors.wiki.ti.com/index.php/PRU_Training:_Hands-on_Labs

Wiring the sensor

There is a good explanation in https://github.com/HudsonWerks/Range-Sensor-PRU, so I'll just quote it:

Hardware configuration:

    * TRIGGER               P8_12 gpio1[12] GPIO44  out     pulldown                Mode: 7 
    * ECHO                  P8_11 gpio1[13] GPIO45  in      pulldown                Mode: 7 *** with R 1KOhm
    * GND                   P9_1 or P9_2    GND
    * VCC                   P9_5 or P9_6    VDD_5V

Schematic:

NOTE: The resistors are important. Since the sensor emits a 5V signal, and the Beaglebone Black's input pins are only 3.3V, using resistors or voltage converters is crucial for preventing damage to your board.

Building and running the example

First setup remoteproc driver by following ../REMOTEPROC.md.

Build and install firmware:

cd hc-sr04-range-sensor
make
sudo cp out/pru-halt.elf /lib/firmware/am335x-pru0-fw
sudo cp out/hc-sr04-range-sensor.elf /lib/firmware/am335x-pru1-fw
sync
reboot # Needed to load the firmware

To see the range measurement result in millimeters:

sudo bash
echo hello > /dev/rpmsg_pru31
cat /dev/rpmsg_pru31   # Press Ctrl+C to exit

Acknowledgements

• Sensor idea and DTS from https://github.com/HudsonWerks/Range-Sensor-PRU
• Remoteproc/RPMsg code from git://git.ti.com/pru-software-support-package/pru-software-support-package.git