Adding New Devices

This page describes how to add new device file nodes to the PetaLinux root filesystem. It is not a tutorial on writing device drivers!

It is assumed that you know the device type (char vs block), major and minor numbers of your new device.

It is further assumed that you have either created a new PetaLinux platform, or are using the PetaLogix / microblaze-auto combination.

Adding the new device node

Edit the petalinux-dist vendors Makefile for your platform - it will be called

petalinux-dist/vendor/${VENDOR}/${PLATFORM}/Makefile

where ${VENDOR} and ${PLATFORM} are the vendor and platform names respectively that you gave to the petalinux-new-platform script. If you are using the default "microblaze-auto" platform, then this will be "PetaLogix" / "microblaze-auto" instead.

The file will look something like this:

#
# Makefile -- Build instructions for Generic uClinux-auto MicroBlaze system
#
                                                                                
include $(VEND)/PetaLogix/common/common.mak
                                                                               
romfs::
                                                                                
clean::
                                                                                

To add a new device node, add a line like the following, after the "include" directive:

#
# Makefile -- Build instructions for Generic uClinux-auto MicroBlaze system
#
                                                                                
include $(VEND)/PetaLogix/common/common.mak

DEVICES += mydev,c,20,0             <<<---- ADD NEW DEVICES HERE
                                                                               
romfs::
                                                                                
clean::
                                                                                

In this example, a new device node called "mydev", corresponding to character device with major number 20, and minor number 0, will be created.

The full syntax is

DEVICES += devname,type,maj,min

where::

devname is the name of the device node type is either b (for block devices) or c (for character devices) maj is the device major number min is the device minor number

Rebuild the filesystem image with the new device nodes

After editting and saving the Makefile, rebuild the romfs and image:

  $ make romfs image

  ...

You may chain multiple device declarations into a single string, e.g.:

  DEVICES += mydev0,c,20,0     mydev1,c,20,1

and so on.

Things to watch out for

1. The DEVICES variable name must be in upper case
2. Ensure you use the "+=" symbol, not "=" or ":="
3. Spaces and other special characters are not permitted in the "devname,type,maj,min" string
4. This procedure only creates a filesystem node for the device entry - you must still write, enable, build and debug the actual kernel driver for the device.