Add_Driv.txt
September 21, 2001

This is a brief description of the steps required to add a driver to those
already provided by the uClinux distribution. The primary reason for wanting
to do this is to be able to support special hardware and include support
for interrupts. It is presumed that the reader is familiar with:
   Linux Device Drivers
   by Alessandro Rubini
   First edition, (C)1998
   ISBN: 1-56592-292-1
as far as the basics of a device driver. (There are newer editions out there,
but this is the one I used.)

All of the following steps must be performed. There is no specific order, but
each will be explained in terms of its impact on the build process. This may
also provide a rudimentary understanding of the 'make' process.

In all of the discussion below, the term 'xyz' is used to refer to the driver
being added. The term has no other meaning than the driver we added. For
your specific project, substitute your name for 'xyz' or 'XYZ'. Also, all
directories are relative to /uClinux-coldfire, the root directory for
uClinux development.

First of all, create the code in the correct place on the source 
tree. Ours is basically a char type driver, so we defined the file:
./linux/drivers/char/xyz.c

Next edit the Makefile in that subdirectory to allow for the new file. In
this case we added the lines:
----
ifdef CONFIG_XYZ
L_OBJS += xyz.o
endif
----
This implies that I'll be using the CONFIG_XYZ parameter to define whether
or not this driver should be included.

In the ./linux/init/main.c you'll need to add the call to the routine to
register your driver with the kernel. In this case we modified the file
linux/init/main.c to add the lines:
----
#ifdef CONFIG_XYZ
extern void xyz_init(void);
#endif
----
#ifdef CONFIG_XYZ
        xyz_init();
#endif
----
These are added at the appropriate places in the file. We tried to follow
the convention already established by the original authors.

Now, you need to inform the make process that this is to be included in the
build. This is done by editing the file ./linux/arch/m68knommu/config.in
so that it includes:
	bool 'XYZ driver' CONFIG_XYZ
This informs the 'make config' process that this choice is to be included in
the section covering the kernel options and that the selection is a [Y/N]
choice.

This puts all the code in place, but the application will need to call the
open() function with a device name. This is done by adding an entry in
romfs_cvs.mk. In our case, we wanted to give this device the name /dev/xyz,
so we added an entry in the device list as '/dev/xyz,c,120,0'. We added
this just before the entry for ppp and were sure to add the backslash (\)
for line continuation.

OK, now you need to run 'make config' and be sure to select customizing the
kernel. If all works well, the system should prompt you for your driver.
If you answer [Y], when it is completed you should see the following entries:

In ./linux/include/linux/autoconf.h:
#define CONFIG_XYZ 1

In ./linux/.config:
CONFIG_XYZ=y

In ./vendors/Motorola/M5272/linux.config:
CONFIG_XYZ=y

In ./lib/libc/include/linux/autoconf.h:
#define CONFIG_XYZ 1

After changing the configuration, it is important to run the entire sequence
of 'make dep', 'make romfs', 'make clean' and finally 'make'. If all goes
well, your driver will be there and you're ready to start testing it!