* 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/)

* 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

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

cd hcsr04-master
make

make install

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

./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.

>> 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

>> 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.