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Running a Program; Configuring Pins

There are a lot of details in compiling and running PRU code. Fortunately those details are captured in a common Makefile that is used throughout this book. This chapter shows how to use the Makefile to compile code and also start and stop the PRUs.

Getting Example Code


I want to get the files used in this book.


It’s all on a GitHub repository.

bone$ cd /opt/source
bone$ git clone
bone$ cd pru-cookbook-code
bone$ sudo ./


#TODO#: The version of code used needs to be noted in the documentation.


#TODO#: Why is this documented in multiple places?

Compiling with clpru and lnkpru


You need details on the c compiler, linker and other tools for the PRU.


The PRU compiler and linker are already installed on many images. They are called clpru and lnkpru. Do the following to see if clpru is installed.

bone$ which clpru


If clpru isn’t installed, follow the instructions at to install it.

bone$ sudo apt update
bone$ sudo apt install ti-pru-cgt-installer

Details on each can be found here:

In fact there are PRU versions of many of the standard code generation tools.

code tools

bone$ ls /usr/bin/*pru
/usr/bin/abspru    /usr/bin/clistpru  /usr/bin/hexpru      /usr/bin/ofdpru
/usr/bin/acpiapru  /usr/bin/clpru     /usr/bin/ilkpru      /usr/bin/optpru
/usr/bin/arpru     /usr/bin/dempru    /usr/bin/libinfopru  /usr/bin/rc_test_encoders_pru
/usr/bin/asmpru    /usr/bin/dispru    /usr/bin/lnkpru      /usr/bin/strippru
/usr/bin/cgpru     /usr/bin/embedpru  /usr/bin/nmpru       /usr/bin/xrefpru

See the PRU Assembly Language Tools for more details.

Making sure the PRUs are configured


When running the Makefile for the PRU you get and error about /dev/remoteproc is missing.


Edit /boot/uEnv.txt and enble pru_rproc by doing the following.

bone$ sudo vi /boot/uEnv.txt

Around line 40 you will see:

###pru_rproc (4.19.x-ti kernel)

Uncomment the uboot_overlay line as shown and then reboot. /dev/remoteproc should now be there.

bone$ sudo reboot
bone$ ls -ls /dev/remoteproc/
total 0
0 lrwxrwxrwx 1 root root 33 Jul 29 16:12 pruss-core0 -> /sys/class/remoteproc/remoteproc1
0 lrwxrwxrwx 1 root root 33 Jul 29 16:12 pruss-core1 -> /sys/class/remoteproc/remoteproc2

Compiling and Running


I want to compile and run an example.


Change to the directory of the code you want to run.

bone$ cd pru-cookbook-code/06io
bone$ ls
gpio.pru0.c  Makefile

Source the setup file.

bone$ source
PocketBeagle Found
Current mode for P2_05 is:     gpio
Current mode for P2_05 is:     gpio

Now you are ready to compile and run. This is automated for you in the Makefile

bone$ make
/opt/source/pru-cookbook-code/common/Makefile:27: MODEL=TI_AM335x_BeagleBone_Green_Wireless,TARGET=gpio.pru0,COMMON=/opt/source/pru-cookbook-code/common
-    Stopping PRU 0
CC  gpio.pru0.c
"/opt/source/pru-cookbook-code/common/prugpio.h", line 53: warning #1181-D: #warning directive: "Found else"
LD  /tmp/vsx-examples/gpio.pru0.o
-   copying firmware file /tmp/vsx-examples/gpio.pru0.out to /lib/firmware/am335x-pru0-fw
-    Starting PRU 0
MODEL   = TI_AM335x_BeagleBone_Green_Wireless
PROC    = pru
PRUN    = 0
PRU_DIR = /sys/class/remoteproc/remoteproc1
rm /tmp/vsx-examples/gpio.pru0.o

Congratulations, your are now running a PRU. If you have an LED attached to P9_11 on the Black, or P2_05 on the Pocket, it should be blinking.


The file sets the TARGET to the file you want to compile. Set it to the filename, without the .c extension (gpio.pru0). The file extension .pru0 specifies the number of the PRU you are using (either 1_0, 1_1, 2_0, 2_1 on the AI or 0 or 1 on the others)

You can override the TARGET on the command line.

bone$ cp gpio.pru0.c gpio.pru1.c
bone$ export TARGET=gpio.pru1

Notice the TARGET doesn’t have the .c on the end.

You can also specify them when running make.

bone$ cp gpio.pru0.c gpio.pru1.c
bone$ make TARGET=gpio.pru1

The setup file also contains instructions to figure out which Beagle you are running and then configure the pins accordingly.

Listing 79
 3export TARGET=gpio.pru0
 6# Configure the PRU pins based on which Beagle is running
 7machine=$(awk '{print $NF}' /proc/device-tree/model)
 8echo -n $machine
 9if [ $machine = "Black" ]; then
10    echo " Found"
11    pins="P9_11"
12elif [ $machine = "Blue" ]; then
13    echo " Found"
14    pins=""
15elif [ $machine = "PocketBeagle" ]; then
16    echo " Found"
17    pins="P2_05"
19    echo " Not Found"
20    pins=""
23for pin in $pins
25    echo $pin
26    config-pin $pin gpio
27    config-pin -q $pin




Set which PRU to use and which file to compile.


Figure out which type of Beagle we have.


Based on the type, set the pins.


Configure (set the pin mux) for each of the pins.


The BeagleBone AI has it’s pins preconfigured at boot time, so there’s no need to use config-pin.

The Makefile stops the PRU, compiles the file and moves it where it will be loaded, and then restarts the PRU.

Stopping and Starting the PRU


I want to stop and start the PRU.


It’s easy, if you already have TARGET set up:

bone$ make stop
-    Stopping PRU 0
bone$ make start
-    Starting PRU 0

See dmesg Hw to see how to tell if the PRU is stopped.

This assumes TARGET is set to the PRU you are using. If you want to control the other PRU use:

bone$ cp gpio.pru0.c gpio.pru1.c
bone$ make TARGET=gpio.pru1
bone$ make TARGET=gpio.pru1 stop
bone$ make TARGET=gpio.pru1 start

The Standard Makefile


There are all sorts of options that need to be set when compiling a program. How can I be sure to get them all right?


The surest way to make sure everything is right is to use our standard Makefile.


It’s assumed you already know how Makefiles work. If not, there are many resources online that can bring you up to speed. Here is the local Makefile used throughout this book.

Listing 80 Local Makefile
1include /opt/source/pru-cookbook-code/common/Makefile


Each of the local Makefiles refer to the same standard Makefile. The details of how the Makefile works is beyond the scope of this cookbook.

Fortunately you shouldn’t have to modify the Makefile.

The Linker Command File - am335x_pru.cmd


The linker needs to be told where in memory to place the code and variables.


am335x_pru.cmd is the standard linker command file that tells the linker where to put what for the BeagleBone Black and Blue, and the Pocket. The am57xx_pru.cmd does the same for the AI. <<<<<<< HEAD Both files can be found in /var/lib/code-server/common. ======= Both files can be found in /opt/source/pru-cookbook-code/common. >>>>>>> bf423e10a7d607eb485449d3f53e7823264dfebb

Listing 81 am335x_pru.cmd
 2/*  AM335x_PRU.cmd                                                          */
 3/*  Copyright (c) 2015  Texas Instruments Incorporated                      */
 4/*                                                                          */
 5/*    Description: This file is a linker command file that can be used for  */
 6/*                 linking PRU programs built with the C compiler and       */
 7/*                 the resulting .out file on an AM335x device.             */
10-cr								/* Link using C conventions */
12/* Specify the System Memory Map */
15      PAGE 0:
16	PRU_IMEM		: org = 0x00000000 len = 0x00002000  /* 8kB PRU0 Instruction RAM */
18      PAGE 1:
20	/* RAM */
22	PRU_DMEM_0_1	: org = 0x00000000 len = 0x00002000 CREGISTER=24 /* 8kB PRU Data RAM 0_1 */
23	PRU_DMEM_1_0	: org = 0x00002000 len = 0x00002000	CREGISTER=25 /* 8kB PRU Data RAM 1_0 */
25	  PAGE 2:
26	PRU_SHAREDMEM	: org = 0x00010000 len = 0x00003000 CREGISTER=28 /* 12kB Shared RAM */
28	DDR			    : org = 0x80000000 len = 0x00000100	CREGISTER=31
29	L3OCMC			: org = 0x40000000 len = 0x00010000	CREGISTER=30
32	/* Peripherals */
34	PRU_CFG			: org = 0x00026000 len = 0x00000044	CREGISTER=4
35	PRU_ECAP		: org = 0x00030000 len = 0x00000060	CREGISTER=3
36	PRU_IEP			: org = 0x0002E000 len = 0x0000031C	CREGISTER=26
37	PRU_INTC		: org = 0x00020000 len = 0x00001504	CREGISTER=0
38	PRU_UART		: org = 0x00028000 len = 0x00000038	CREGISTER=7
40	DCAN0			: org = 0x481CC000 len = 0x000001E8	CREGISTER=14
41	DCAN1			: org = 0x481D0000 len = 0x000001E8	CREGISTER=15
42	DMTIMER2		: org = 0x48040000 len = 0x0000005C	CREGISTER=1
43	PWMSS0			: org = 0x48300000 len = 0x000002C4	CREGISTER=18
44	PWMSS1			: org = 0x48302000 len = 0x000002C4	CREGISTER=19
45	PWMSS2			: org = 0x48304000 len = 0x000002C4	CREGISTER=20
46	GEMAC			: org = 0x4A100000 len = 0x0000128C	CREGISTER=9
47	I2C1			: org = 0x4802A000 len = 0x000000D8	CREGISTER=2
48	I2C2			: org = 0x4819C000 len = 0x000000D8	CREGISTER=17
49	MBX0			: org = 0x480C8000 len = 0x00000140	CREGISTER=22
50	MCASP0_DMA		: org = 0x46000000 len = 0x00000100	CREGISTER=8
51	MCSPI0			: org = 0x48030000 len = 0x000001A4	CREGISTER=6
52	MCSPI1			: org = 0x481A0000 len = 0x000001A4	CREGISTER=16
53	MMCHS0			: org = 0x48060000 len = 0x00000300	CREGISTER=5
54	SPINLOCK		: org = 0x480CA000 len = 0x00000880	CREGISTER=23
55	TPCC			: org = 0x49000000 len = 0x00001098	CREGISTER=29
56	UART1			: org = 0x48022000 len = 0x00000088	CREGISTER=11
57	UART2			: org = 0x48024000 len = 0x00000088	CREGISTER=12
59	RSVD10			: org = 0x48318000 len = 0x00000100	CREGISTER=10
60	RSVD13			: org = 0x48310000 len = 0x00000100	CREGISTER=13
61	RSVD21			: org = 0x00032400 len = 0x00000100	CREGISTER=21
62	RSVD27			: org = 0x00032000 len = 0x00000100	CREGISTER=27
66/* Specify the sections allocation into memory */
68	/* Forces _c_int00 to the start of PRU IRAM. Not necessary when loading
69	   an ELF file, but useful when loading a binary */
70	.text:_c_int00*	>  0x0, PAGE 0
72	.text		>  PRU_IMEM, PAGE 0
73	.stack		>  PRU_DMEM_0_1, PAGE 1
74	.bss		>  PRU_DMEM_0_1, PAGE 1
75	.cio		>  PRU_DMEM_0_1, PAGE 1
76	.data		>  PRU_DMEM_0_1, PAGE 1
77	.switch		>  PRU_DMEM_0_1, PAGE 1
78	.sysmem		>  PRU_DMEM_0_1, PAGE 1
79	.cinit		>  PRU_DMEM_0_1, PAGE 1
80	.rodata		>  PRU_DMEM_0_1, PAGE 1
81	.rofardata	>  PRU_DMEM_0_1, PAGE 1
82	.farbss		>  PRU_DMEM_0_1, PAGE 1
83	.fardata	>  PRU_DMEM_0_1, PAGE 1
85	.resource_table > PRU_DMEM_0_1, PAGE 1
86	.init_pins > PRU_DMEM_0_1, PAGE 1


The cmd file for the AI is about the same, with appropriate addresses for the AI.


The important things to notice in the file are given in the following table.

AM335x_PRU.cmd important things




This is where the instructions are stored. See page 206 of the AM335x Technical Reference Manual rev. P Or see page 417 of AM572x Technical Reference Manual for the AI.


This is where PRU 0’s DMEM 0 is mapped. It’s also where PRU 1’s DMEM 1 is mapped.


The reverse to above. PRU 0’s DMEM 1 appears here and PRU 1’s DMEM 0 is here.


The shared memory for both PRU’s appears here.


The .text section is where the code goes. It’s mapped to IMEM


The ((stack)) is then mapped to DMEM 0. Notice that DMEM 0 is one bank

of memory for PRU 0 and another for PRU1, so they both get their own stacks.


The .bss section is where the heap goes.

Why is it important to understand this file? If you are going to store things in DMEM, you need to be sure to start at address 0x0200 since the stack and the heap are in the locations below 0x0200.

Loading Firmware


I have my PRU code all compiled and need to load it on the PRU.


It’s a simple three step process.

  • Stop the PRU

  • Write the .out file to the right place in /lib/firmware

  • Start the PRU.

This is all handled in the The Standard Makefile.


The PRUs appear in the Linux file space at /dev/remoteproc/.

Finding the PRUs

bone$ cd /dev/remoteproc/
bone$ ls
pruss-core0  pruss-core1

Or if you are on the AI:

bone$ cd /dev/remoteproc/
bone$ ls
dsp1  dsp2  ipu1  ipu2  pruss1-core0  pruss1-core1  pruss2-core0  pruss2-core1

You see there that the AI has two pairs of PRUs, plus a couple of DSPs and other goodies.

Here we see PRU 0 and PRU 1 in the path. Let’s follow PRU 0.

bone$ cd pruss-core0
bone$ ls
device  firmware  name  power  state  subsystem  uevent

Here we see the files that control PRU 0. firmware tells where in /lib/firmware to look for the code to run on the PRU.

bone$ cat firmware

Therefore you copy your .out file to /lib/firmware/am335x-pru0-fw.

Configuring Pins for Controlling Servos


You want to configure the pins so the PRU outputs are accessible.


It depends on which Beagle you are running on. If you are on the AI or Blue, everything is already configured for you. If you are on the Black or Pocket you’ll need to run the following script.

Listing 82
 2# Configure the PRU pins based on which Beagle is running
 3machine=$(awk '{print $NF}' /proc/device-tree/model)
 4echo -n $machine
 5if [ $machine = "Black" ]; then
 6    echo " Found"
 7    pins="P8_27 P8_28 P8_29 P8_30 P8_39 P8_40 P8_41 P8_42"
 8elif [ $machine = "Blue" ]; then
 9    echo " Found"
10    pins=""
11elif [ $machine = "PocketBeagle" ]; then
12    echo " Found"
13    pins="P2_35 P1_35 P1_02 P1_04"
15    echo " Not Found"
16    pins=""
19for pin in $pins
21    echo $pin
22    config-pin $pin pruout
23    config-pin -q $pin


The first part of the code looks in /proc/device-tree/model to see which Beagle is running. Based on that it assigns pins a list of pins to configure. Then the last part of the script loops through each of the pins and configures it.

Configuring Pins for Controlling Encoders


You want to configure the pins so the PRU inputs are accessible.


It depends on which Beagle you are running on. If you are on the AI or Blue, everything is already configured for you. If you are on the Black or Pocket you’ll need to run the following script.

Listing 83
 2# Configure the pins based on which Beagle is running
 3machine=$(awk '{print $NF}' /proc/device-tree/model)
 4echo -n $machine
 6# Configure eQEP pins
 7if [ $machine = "Black" ]; then
 8    echo " Found"
 9    pins="P9_92 P9_27 P8_35 P8_33 P8_12 P8_11 P8_41 P8_42"
10elif [ $machine = "Blue" ]; then
11    echo " Found"
12    pins=""
13elif [ $machine = "PocketBeagle" ]; then
14    echo " Found"
15    pins="P1_31 P2_34 P2_10 P2_24 P2_33"
17    echo " Not Found"
18    pins=""
21for pin in $pins
23    echo $pin
24    config-pin $pin qep
25    config-pin -q $pin
29# Configure PRU pins
30if [ $machine = "Black" ]; then
31    echo " Found"
32    pins="P8_16 P8_15"
33elif [ $machine = "Blue" ]; then
34    echo " Found"
35    pins=""
36elif [ $machine = "PocketBeagle" ]; then
37    echo " Found"
38    pins="P2_09 P2_18"
40    echo " Not Found"
41    pins=""
44for pin in $pins
46    echo $pin
47    config-pin $pin pruin
48    config-pin -q $pin


This works like the servo setup except some of the pins are configured as to the hardware eQEPs and other to the PRU inputs.