Re: char devices and debugging

[Gordon H. <go...@gh...>]

fh...@at... wrote:
> 
> I have been trying to learn how to program char devices.
> Well really trying to get my Hypercom4+ and Delfina Plus cards
>  to work.  I've made test drivers for both.  Both drivers contain printk
> statements so I can see if they are doing anything remotely like they are
> supposed to.  Even though the drivers seem to  compile OK and are
> "installed" in the kernel, no printk statements are visible in the dmesg
> output.  Is this a problem peculiar to char devices?  I suspect I have not
> quite got the driver code installed correctly in the kernel source tree.

Try changing the printk's to
printk(KERN_INFO "Blah"); /* KERN_* are defined in linux/kernel.h */

then it may goto dmesg and the kernel log.

> Can anyone tell me the general procedure for adding a driver
> to the kernel?  i.e. so it can be chosen in the .config and loaded into
> the kernel?  Or maybe point me to some docs somewhere.

Sure, for 2.2 add a config option in arch/ppc/config.in and change
drivers/char/Makefile.

Or compile it as a module.

with gcc -c module.c -DMODULE -D__KERNEL__ -o module.o
then load the mod with /sbin/insmod module.o

Module programing infos at http://www.linuxdoc.org/LDP/lkmpg/mpg.html

Gordon