Beaglebone black - Debian 4.1 - PRU - prussdrv_open() failed with -1 - linux

Question

I am running the example as root http://mythopoeic.org/BBB-PRU/pru-helloworld/example.c
and I receive the Error:
"prussdrv_open() failed with -1" during the execution
BBB has Debian 4.1
These are the commands used:
sudo cp EBB-PRU-Example‐00A0.dtbo /lib/firmware
echo EBB-PRU-Example > /sys/devices/platform/bone_capemgr/slots
cat /sys/devices/platform/bone_capemgr/slots
0: PF---- -1
1: PF---- -1
2: PF---- -1
3: PF---- -1
4: P-O-L- 0 Override Board Name,00A0,Override Manuf,EBB-PRU-Example
modprobe uio_pruss
dmesg
[ 195.985512] bone_capemgr bone_capemgr: part_number 'EBB-PRU-Example', version 'N/A'
[ 195.994182] bone_capemgr bone_capemgr: slot #4: override
[ 195.999703] bone_capemgr bone_capemgr: Using override eeprom data at slot 4
[ 196.006752] bone_capemgr bone_capemgr: slot #4: 'Override Board Name,00A0,Override Manuf,EBB-PRU-Example'
[ 196.039095] pruss_uio 4a300000.pruss: No children
[ 196.057144] gpio-of-helper ocp:gpio_helper: ready
[ 196.070956] bone_capemgr bone_capemgr: slot #4: dtbo 'EBB-PRU-Example-00A0.dtbo' loaded; overlay id #0
and
/boot/uEnv.txt has disabled the HDMI
EBB-PRU-Example.dts
/* Device Tree Overlay for enabling the pins that are used in Chapter 13
* This overlay is based on the BB-PRU-01 overlay
* Written by Derek Molloy for the book "Exploring BeagleBone: Tools and
* Techniques for Building with Embedded Linux" by John Wiley & Sons, 2014
* ISBN 9781118935125. Please see the file README.md in the repository root
* directory for copyright and GNU GPLv3 license information.
*/
/dts-v1/;
/plugin/;
/ {
compatible = "ti,beaglebone", "ti,beaglebone-black";
part-number = "EBB-PRU-Example";
version = "00A0";
/* This overlay uses the following resources */
exclusive-use =
"P9.11", "P9.13", "P9.27", "P9.28", "pru0";
fragment#0 {
target = <&am33xx_pinmux>;
__overlay__ {
gpio_pins: pinmux_gpio_pins { // The GPIO pins
pinctrl-single,pins = <
0x070 0x07 // P9_11 MODE7 | OUTPUT | GPIO pull-down
0x074 0x27 // P9_13 MODE7 | INPUT | GPIO pull-down
>;
};
pru_pru_pins: pinmux_pru_pru_pins { // The PRU pin modes
pinctrl-single,pins = <
0x1a4 0x05 // P9_27 pr1_pru0_pru_r30_5, MODE5 | OUTPUT | PRU
0x19c 0x26 // P9_28 pr1_pru0_pru_r31_3, MODE6 | INPUT | PRU
>;
};
};
};
fragment#1 { // Enable the PRUSS
target = <&pruss>;
__overlay__ {
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&pru_pru_pins>;
};
};
fragment#2 { // Enable the GPIOs
target = <&ocp>;
__overlay__ {
gpio_helper {
compatible = "gpio-of-helper";
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&gpio_pins>;
};
};
};
};

Answer 1

There are two pre compiled versions of the 4.1 kernel for the BBB in the repos: The "TI" version and the "Bone" version. The TI version uses a newer API for controlling the PRU and the Bone version has the same API as the 3.8 kernel and the prussdrv_open() function should work fine.
To install the 4.1 "bone" kernel, you can do:
cd /opt/scripts/tools
sudo ./update_kernel.sh --bone-rt-kernel --lts-4_1
More info: https://groups.google.com/forum/#!topic/beagleboard/cyM3f935wMA

Answer 2

Hmmm looks similar to a previous issue.. The problem was that the PRU was not enabled, and I quote :
echo BB-BONE-PRU-01 > /sys/devices/bone_capemgr.8/slots fixed it.

Answer 3

You could try to use the 4.1.5-ti-r10 version of the kernel. Apparently pruss_uio does not work for some 4.1.x kernels.
Moreover, the dts file you are using was not working for me either (don't know why). I used the following, and prussdrv_open does not fail:
/dts-v1/;
/plugin/;
/ {
compatible = "ti,beaglebone", "ti,beaglebone-black";
/* identification */
part-number = "BB-ENABLE-PRU";
/* version */
version = "00A0";
fragment#1 { // Enable the PRUSS
target = <&pruss>;
__overlay__ {
status = "okay";
};
};
};
If found all this out on that thread: https://groups.google.com/forum/#!category-topic/beagleboard/VBNEoCbEHUQ