This post applies to the picopar.tar Linux module distribution.
To get it to make, the line
gcc -O -DMODULE -D__KERNEL__ -o picolnx.o -c picolnx.c
needs to be changed to point to the correct kernel include files, which in my case are at /usr/src/linux-2.4.22/include:
gcc -O -I/usr/src/linux-2.4.22/include -DMODULE -D__KERNEL__ -o picolnx.o -c picolnx.c
A more complete fix was posted by tomset, but that was months ago, and the makefile still hasn't been patched.
When you load the module, you get:
[root@flasher picopar]# insmod ./pico.o
Warning: loading ./pico.o will taint the kernel: no license
for information about tainted modules
Module pico loaded, with warnings
Reviewing the code, I wonder why Pico doesn't GPL or OSS this stuff.
I lack the hardware for the moment, but it builds and loads with RH9, Linux 2.4.22, so this looks pretty good.