Sleeping for <1 jiffie in kernel module

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Hi All,

I'm working on a kernel module to drive a PCI card. The module reads a clock port (frequency: 1187 Hz) and sends a bit to the data port every time the clock port rises. This stream of bits has to flow as long as the PCI card is used – for hours maybe.

The module has to check the clock port to detect a rise. This looks something like this:

while (...) {
    while (port_get() != 0) { }	// wait for the clock to fall
    while (port_get() == 0) { }	// wait for the clock to rise
    *** send bit ***
}

This effectively locks up the computer as it eats all the CPU cycles do do... nothing ;-) Given the clock frequency of 1187Hz, the time between two clock port rises is about 842ns. So a better code that's supposed NOT to eat up all CPU cycles should look something like this:

while (...) {
nanosleep(800);
while (port_get() == 0) { nanosleep(20); } // wait for the clock to rise
*** send bit ***
}


Last but not least: the question!

I can't use nanosleep() in kernel modules and the resolution of schedule_timeout() is way too large. What else can I use instead of nanosleep()?

Many thanks for your help,
-sven


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