Difference between revisions of "Bw tool"

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(Setting up I2C/SPI under Linux)
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'''0''': (on Raspberry Pi) edit /etc/modprobe.d/raspi-blacklist.conf to look like this:
'''0''': (on Raspberry Pi) edit /etc/modprobe.d/raspi-blacklist.conf to look like this:
  # blacklist spi and i2c by default (many users don't need them)
  # blacklist spi and i2c by default (many users don't need them)
  #blacklist spi-bcm2708
  #blacklist spi-bcm2708
  #blacklist i2c-bcm2708
  #blacklist i2c-bcm2708
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'''2''': Reboot
'''2''': Reboot
= Basic Example =
= Basic Example =

Revision as of 15:03, 20 August 2014


The bw_tool is meant to provide a basic commandline access to the bitwizard expansion boards. It was written for the Raspberry Pi, but has now been proven to work on other Linux platforms with an spidev device as well.


You can download the bw_tool here. If you are using git just type

git clone https://github.com/rewolff/bw_rpi_tools.git 

Nowadays the "bw_tool" is the only directory of interest. Go there and build:

cd bw_tool; make 

should work fine. If things went smoothly (which they usually do) you can install the binary so that normal people can find it:

 make install

Setting up I2C/SPI under Linux

To get Linux to work with SPI/I2C the proper modules need to be loaded. To do this automatically on boot:

0: (on Raspberry Pi) edit /etc/modprobe.d/raspi-blacklist.conf to look like this:

# blacklist spi and i2c by default (many users don't need them)
#blacklist spi-bcm2708
#blacklist i2c-bcm2708

1: Add the following lines to /etc/modules:


2: Reboot

Basic Example

The simplest invocation:

bw_tool -t "Hello World!"

will display the shown text on an SPI_LCD on the default SPI bus (SPI0). Options modify the defaults.

About Permissions

The above command needs access to the SPI bus. By default Linux does not know if letting users access this bus is going to compromise the system or not. As a result, Linux chooses to only allow the root user access to the SPI or I2C bus by default. So you have the following choices:

  • You can run your whole session as root. Run "sudo -i" to gain root access.
  • You can issue only the commands that require spi-bus access as root by prefixing them with "sudo". e.g.:
 sudo bw_tool -t "Hello World!"
  • If you are using I2C only, you could add yourself to the I2C group (assuming your username is "pi") :
 sudo gpasswd -a pi i2c


 sudo usermod -a -G i2c pi

You only need to run one of these commands once. Afterwards, log out and back in. To verify if the command succeeded, run:


it should return something like:

 pi adm dialout cdrom sudo audio video plugdev games users i2c
  • you can change the permissions on the device files:
 sudo chmod 666 /dev/spidev*
 sudo chmod 666 /dev/i2c-*

Since the "/dev" filesystem is kept in RAM, you will need to do that again, at every boot. You could add those commands to /etc/rc.local to issue them automatically at every boot, but a better way is to use udev for this. To do that create (as root) the file /etc/udev/rules.d/70-i2cspi.rules with the following contents:

SUBSYSTEM=="spidev", MODE="0666"
SUBSYSTEM=="i2c-dev", MODE="0666"

and reboot. All I2C and SPI devices should now be world writable.


Options Specifying the Device

The option


will switch to I2C mode.

The option

-D <device> 

will use that device. Specify /dev/spidev0.1 for the second SPI bus on the raspberry pi for example. Or /dev/i2c-1 to specify the second I2C bus. On revision 2 Raspberry Pi's, the I2C buses are switched. While on rev. 1 Pi's The option

-a <address> 

specifies the address of the device to use. Note that BitWizard uses the full 8 bits that are sent to the device. Add one for "read" operation. In some circles, notably I2C, it is customary to specify just those 7 bits. Thus when the I2C_LCD is at the default address of 0x82, i2cdetect will scan it at address 0x41.

Identifying the Device

To check for a proper connection to the device, one could use the identify command line switch -i. For instance, a Raspberry Pi UI connected via I2C could be checked with

bw_tool  -I -D /dev/i2c-0 -a 94 -i


I2C_rpi_ui 1.6

Sending Data

the option

-t "text" 

will send the text to the device, at port zero. The port cannot be changed, but all BitWizard PCBs that have the option of displaying text have the text port at port zero.

The option

-w <addr>:<byte> 

will write the byte to the port at addr. For LCD-equipped boards for example -w 12:50 will set the contrast to 0x50.

The option

-W <addr>:<short>

will write the 16-bit short to the port at addr. For example -W 81:1000 will write the value 0x1000 to the numsamples port on an analog-equipped board.

Reading Data

The option

-R <port>:<datasize>

reads the data at port from the device. Datasize can be 'b' for byte (default), 's' for short (16 bits), or 'i' for a 32-bit integer.


To test sending data to SPI devices, there is the

 --hex [byte...]

option. This simply sends the bytes specified, and reports back what was received. Note that BitWizard boards will not send any data until they have been selected, so the first byte received will represent whatever static is found on the bus.

Known Bugs

  • The identify command returns two garbled characters when used in I2C mode