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timer interrupt

hello,

i am working on a drivermodule to control a stepper motor using the 
parallel port. i need a timer mechanism with a higher frequency than the 
jiffies clock. i tried to register an interrupt handler for IRQ0, but 
the code

request_irq(0,stepper_isr,SA_SHIRQ,"stepper",&iNothing)

fails and returns -16 (16 == EBUSY, 12 == ENOMEM, 22 == EINVAL, so i 
guess that the "-" characters in `man request_irq` in the return value 
section are really minus signs, and not some item indicators. i mean: 
can i interpret "-16" as being EBUSY?). i tried also using the flags 
SA_INTERRUPT|SA_SHIRQ, but it gave the same result, so i gues the timer 
interrupt cannot be shared using request_irq().

- can anyone tell me what i am doing wrong?
- or how i can get my interrupt service routine called at each IRQ0 (i 
played a bit with writing interrupt handler in dos using assembler, but 
i don't know if i can do the same things in protected mode. if i 
remember correct, the isr for irq0 can be found at addres 0x0000 till 
0x0003, so can i just replace this with my isr and call the original 
linux timer isr at the end of my isr)?
- (or where i can find the linux timer interrupt handler in the source 
so i can extend this (last option))?

(i run the latest mandrake and/or the latest debian)

greetings and happy newyear,
geert.

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