CPU Frequency Calibration
=========================

The module rt_cal, allows you to check the calibration of the cpu clock.
Just type 'make cal s="SECS=<x>"' to get it and "make stop" to stop and
remove it. <x> is the pacing, in seconds, at which messages are issued. If
"s" is omitted the default (5 s) is used.  Note that on the alphanumeric
screen they appear directly onto it, under X they do not, unless you have
an xconsole installed, but can be seen by typing "dmesg".

In about twenty seconds the frequency value displayed on the console should
converge to at least one part in ten million.  If you keep it running
longer you can verify that more and more digits remain stable. In about a
quarter of an hour you should get a precision to the least significant
digit. For a very precise and safe calibration let it run for an hour or so
with SECS set to a relatively high value to avoid annoying messages.

Such a high precision is not strictly required for RTAI to work
appropriately, in fact RTAI is enough with iLinux calibration values it
uses as defaults.

Note that this modules is also an example of how you can trap a Linux
interrupt and then chain your handler back to Linux by using
"rt_pend_linux_irq(irq)".

To use it:

  make clean
  make
  make cal

Wait till you are happy with the converging value, then do

  make stop
