Beaglebone Black PRU code to use HC-SR04 proximity sensor.

There are many examples around with Beaglebone PRU code to use an HC-SR04 sonar sensor, but most are outdated, do not work or require older beagles or older kernels.
This repository includes everything needed to obtain a working example and can be used as a template for more complex PRU code.

Prerequisites:

* Beaglebone Black with debian 3.8.13 bone47
* HC-SR04 sensor
* Dev tools (gcc, pasm, dtc, etc.) that are already included in BBB latest images.
  (If you miss them, please upgrade from http://beagleboard.org/latest-images/)

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
Make sure there is a 1KOhm resistor between ECHO pin and your beaglebone
as input pins are 3.3V while sensor emits 5V

Schematic:

Schematic

To download the complete package to your Beaglebone Black:

wget --no-check-certificate https://github.com/luigif/hcsr04/archive/master.tar.gz -O - | tar xz

To build:

 cd hcsr04-master
make

To install driver:

make install
It will copy device tree driver to /lib/firmware and add it to the cape manager

To run:

./hcsr04
Note: After a first successful "make install", before running the hcsr04 program, 
you can load the driver with the install-driver.sh script.
Depending on your needs, you can configure your operating system to run the 
install-driver.sh script at boot.

Example build output after running “make”:

>> Compiling Driver
dtc -O dtb -o hcsr04-00A0.dtbo -b 0 -@ hcsr04.dts
>> Generating PRU binary
pasm -b hcsr04.p
PRU Assembler Version 0.84
Copyright (C) 2005-2013 by Texas Instruments Inc.
Pass 2 : 0 Error(s), 0 Warning(s)
Writing Code Image of 43 word(s)
>> Compiling HC-SR04 example
gcc -Wall -c -o hcsr04.o hcsr04.c
gcc -lpthread -lprussdrv -o hcsr04 hcsr04.o

Example output after running “./hcsr04”:

>> Initializing PRU
>> Executing HCSR-04 code
  1: Distance = 181.52 cm
  2: Distance = 181.50 cm
  3: Distance = 181.50 cm
  4: Distance = 181.52 cm
  5: Distance = 181.93 cm
  6: Distance = 181.52 cm
  7: Distance = 180.64 cm
  8: Distance = 181.50 cm
  9: Distance = 181.06 cm
 10: Distance = 181.49 cm
 11: Distance = 181.04 cm
 12: Distance = 181.93 cm
 13: Distance = 181.47 cm
 14: Distance = 181.47 cm
 15: Distance = 181.91 cm
 16: Distance = 181.91 cm
 17: Distance = 181.47 cm
 18: Distance = 182.35 cm
 19: Distance = 181.49 cm
 20: Distance = 181.06 cm
>> PRU Disabled.