BeagleBone Black Notes, Part 2

Picking up from our previous session, it’s time to hack some more.

USB network bridge

A quick couple scripts so we can bridge network through the USB interface.

On the host machine, we create /usr/local/src/usbnet_gate like so:

#!/bin/bash

case "$1" in

up)
    ifconfig usb0 172.17.0.254 netmask 255.255.0.0
    iptables -F
    iptables -t nat -F
    iptables -t mangle -F
    iptables -X
    iptables -t nat -X
    iptables -t mangle -X

    iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
    iptables -A FORWARD -i usb0 -j ACCEPT

    echo 1 > /proc/sys/net/ipv4/ip_forward

    if ( ifconfig wlan0 | grep -q DOWN ); then
        echo "Don't forget to put up the wlan0 interface!"
    fi
    ;;

down)
    iptables -F
    iptables -t nat -F
    iptables -t mangle -F
    
    iptables -X
    iptables -t nat -X
    iptables -t mangle -X
    ifconfig eth0 down
    ;;

*)
    echo "Usage: $0 {up|down}"
    exit 1
    ;;

esac

exit 0

On the target board, /usr/local/src/usbnet_route looks like this:

#!/bin/bash

case "$1" in

up)

    # fix routing table
    for i in $(route -n | grep UG | sed 's/  */,/g'); do
        $(echo $i | awk -F , '{print("route del -net",$1,"netmask",$3,"gw",$2);}');
    done

    route add default gw 172.17.0.254
    ;;

down)

    # fix routing table
    for i in $(route -n | grep UG | sed 's/  */,/g'); do
        $(echo $i | awk -F , '{print("route del -net",$1,"netmask",$3,"gw",$2);}');
    done
    ;;

*)
    echo "Usage: $0 {up|down}"
    exit 1
    ;;

esac

exit 0

If you don’t regularly connect an ethernet cable to your BBK at boot, you could run this script automatically by adding

post-up /usr/local/src/usbnet_route up

in the usb0 stanza in /etc/network/interfaces. Otherwise, just go in via serial or SSH and enable it.

PRU access under Wheezy

One of the coolest features of the AM335x SOC on the BBK is the pair of Programmable Realtime Units (PRUs), 200 MHz RISC cores that run independently of the ARM core and with access to GPIO, peripherals, private memory, and system memory. These are really cool for making high-speed hardware interfaces or communications busses.

More background info on the PRUs is available from

ECE497 BeagleBone PRU at elinux.org
First Steps with the BeagleBone PRU courtesy of boxysean
am335x_pru_package from the BeagleBoard.org team
boxysean’s fork of am335x_pru_package

The first goal is to get the latter package working with the Debian Wheezy image we installed last time. Grabbing the am335x_pru_package, we follow the build process that boxysean describes (see the “First Steps” link above). If you grab boxysean’s fork of the package you get a couple LED blinking tests as well.

Sadly, it doesn’t work right out of the box: once we’re ready to run the test code, it turns out that the uio_pruss module shipped with our image apparently doesn’t work right.

INFO: Starting PRU_memAccessPRUDataRam example.
prussdrv_open open failed

A little straceing reveals the problem:

open("/dev/uio0", O_RDWR|O_SYNC)        = -1 ENODEV (No such device)
open("/sys/class/uio/uio0/maps/map0/addr", O_RDONLY) = -1 ENOENT (No such file or directory)

Apparently something about the uio implementation is broken. Let’s see if we can’t figure out what.

My first inclination is to investigate how it works with the default Ångstrom image (aren’t you glad we kept our install on a microSD card? I am!).

Updating the eMMC from Debian (but not really)

First things first: you should be sure your Ångstrom image is up-to-date.

After looking into it, it turns out that my board already has the latest image. However, before figuring this out, I set about coming up with a way to update the onboard Ångstrom image directly from our Debian install. I’ve recorded it here for posterity.

On the target board, download the latest image:
```
cd /usr/local/src
wget https://s3.amazonaws.com/angstrom/demo/beaglebone/Angstrom-Cloud9-IDE-GNOME-eglibc-ipk-v2012.12-beaglebone-2013.04.13.img.xz
```
Note: if wget complains about certificates, it’s probably because the date on your machine isn’t set. ntpdate -s time.mit.edu will fix you right up.

Decompress it:

xz -d Angstrom-Cloud9-IDE-GNOME-eglibc-ipk-v2012.12-beaglebone-2013.04.13.img.xz

Now we have an .img file that’s actually a disk with a partition table and two partitions. Using fdisk (yes, you can run fdisk on a regular file!) we can see that the two partitions start at offsets 63 and 144585, both expressed in units of 512 bytes. With this information, we can mount the partitions like so (note the offset we provide is 144585*512):
```
mkdir -p /mnt/Afiles
mount -o loop,offset=74027520 BBB-eMMC-flasher-2013.04.13-DDR3-400MHz.img /mnt/Afiles
```
In /mnt/Afiles/build we find the actual scripts that are used to flash the drive. Simply running emmc.sh should perform the update. Since I haven’t actually done this, your mileage may vary.

Getting the PRUSS working

I booted the Ångstrom system expecting things to work, but no love here. modprobe uio_pruss still resulted in an empty /sys/class/uio directory!

A little more research turned up this thread, How to reliably activate PRUSS on beaglebone? (from today!). Apparently there are some troubles with PRUSS under 3.8 kernels; until they’re fixed, we can use Jacek Radzikowski’s magical hack. Create /usr/local/src/pruss_magic_jr, like so:

#!/bin/bash

progress_and_delay () {
    echo -n "."
    sleep 1
}

SLOTS=/sys/devices/bone_capemgr.*/slots

echo -n "Installing uio_pruss module ."

/sbin/modprobe uio_pruss
progress_and_delay

rmmod uio_pruss
progress_and_delay

echo cape-bone-nixie > $SLOTS
progress_and_delay

/sbin/modprobe uio_pruss
progress_and_delay

echo cape-bone-nixie > $SLOTS
progress_and_delay

rmmod uio_pruss
progress_and_delay

/sbin/modprobe uio_pruss
progress_and_delay

( [ -L /sys/class/uio/uio0 ] || [ -d /sys/class/uio/uio0 ] ) && echo ' Success!' && exit 0

# shouldn't get here if things worked
echo 'Failed.'
exit 1;

After executing this, the PRUs work!

[root@charm]# ls /sys/class/uio/uio0/
total 0
drwxr-xr-x  4 root root    0 Jan  1 00:09 .
drwxr-xr-x 10 root root    0 Jan  1 00:09 ..
-r--r--r--  1 root root 4096 Jan  1 00:22 dev
lrwxrwxrwx  1 root root    0 Jan  1 00:22 device -> ../../../4a300000.pruss
-r--r--r--  1 root root 4096 Jan  1 00:22 event
drwxr-xr-x  4 root root    0 Jan  1 00:22 maps
-r--r--r--  1 root root 4096 Jan  1 00:22 name
drwxr-xr-x  2 root root    0 Jan  1 00:22 power
lrwxrwxrwx  1 root root    0 Jan  1 00:09 subsystem -> ../../../../../class/uio
-rw-r--r--  1 root root 4096 Jan  1 00:09 uevent
-r--r--r--  1 root root 4096 Jan  1 00:22 version
[root@charm]# ./PRU_PRUtoPRU_Interrupt 

INFO: Starting PRU_PRUtoPRU_Interrupt example.
AM33XX
AM33XX
        INFO: Initializing example.
        INFO: Executing example on PRU0.
File ./PRU_PRU0toPRU1_Interrupt.bin open passed
                INFO: Executing example on PRU1.
File ./PRU_PRU1toPRU0_Interrupt.bin open passed
        INFO: Waiting for HALT command.
        INFO: PRU0 completed transfer.
                INFO: Waiting for HALT command.
                INFO: PRU1 completed transfer.
Example executed succesfully.

Well, that’s all the time I’ve got today. My goal in the near term is to use the PRUSS to do high-speed data capture and waveform generation. After that, I hope to wrap the whole thing in a nice web interface so that we can use the board as a pattern generator / logic capture card via a web browser.

Stay tuned!

←

Questions? Comments?
@kwantam | <kwantam@gmail.com> | github

BeagleBone Black Notes, Part 2

Riad Wahby

2013 May 4

USB network bridge

PRU access under Wheezy

Updating the eMMC from Debian (but not really)

Getting the PRUSS working