Arduino Communications Device Naming with udev

Summary
This article covers the installation and basic usage of the Bus Pirate.

The Bus Pirate is a versatile tool for communicating with various hardware.

Interfacing a new microchip can be a hassle. Breadboarding a circuit, writing code, hauling out the programmer, or maybe even prototyping a PCB. We never seem to get it right on the first try.

The ‘Bus Pirate’ is a universal bus interface that talks to most chips from a PC serial terminal, eliminating a ton of early prototyping effort when working with new or unknown chips. Many serial protocols are supported at 0-5.5volts, more can be added. See more at the google code site for the Bus Pirate.

Installation

The drivers for the FTDI chip is included in the kernel, so it should be detected as soon as it's plugged in, and assigned to device /dev/ttyUSB[0-9]. To check where it got assigned, run:

# dmesg | tail

The output will contain a line that looks something like this:

# usb 1-4.4: FTDI USB Serial Device converter now attached to ttyUSB0

udev

It can be annoying to have to look up what /dev/ttyUSB[0-9] the device gets assigned, so it's a good idea to add a simple udev rule that creates the symlink '/dev/buspirate -> /dev/ttyUSB*' when it is plugged in.

First of all, you will need to find out the serial number of FTDI chip on the bus pirate. This can be achieved by running the following, assuming your device is plugged in and was assigned to /dev/ttyUSB0:

# udevadm info --attribute-walk -n /dev/ttyUSB0  | sed -n '/FTDI/,/serial/p'

Now add/create the following file:

/etc/udev/rules.d/98-buspirate.rules

SUBSYSTEM=="tty", ATTRS{serial}=="XXXXXXXX", GROUP="users", MODE="0660", SYMLINK+="buspirate"

Change 'ATTRS{serial}=="XXXXXXXX"' to the serial on your device and force udev to load the new rule:

# udevadm control --reload-rules

At this point, whenever you plug in the device, the symlink should be created.

Communication

To communicate with the device, you can use any of the following, to name a few:

• minicom

# minicom -b 115200 -8 -D /dev/buspirate

• screen

# screen /dev/buspirate 115200 8N1

• picocom

# picocom -b 115200 -p n -d 8 /dev/buspirate

Type '?' and press enter and the device should reply with a list of possible commands.