[time-nuts] Using a frequency synthesizer replacement for motherboard oscillator

Hal Murray hmurray at megapathdsl.net
Sun Dec 2 03:10:54 UTC 2012

davidwhess at gmail.com said:
> One of my favorite tricks back when the ISA bus was still available was to
> use a custom expansion board I built and an oscilloscope to measure the
> interrupt latency. 

You can do the same trick without special hardware.  Use the printer port.  
Of course, that assumes your PC/Laptop still has a printer port.

I have a laptop with a printer port on the thing Dell calls a MediaBase.  
It's an extender/fattener that includes a CD drive with connectors for 
printer port and serial port.  It plugs into a big connector on the bottom of 
the laptop.

Many laptops plug into docking stations for use at a desk.  Sometimes/often 
they have printer ports and/or serial ports.

You could probably do it with just a serial port by flapping one of the 
output modem control signals.

If you don't have a printer port or serial port, how are you getting the 
interrupt into your box?


Many years ago, I helped a friend with this sort of thing.  We were working 
for DEC back in the days before Intel had captured everything and 
workstations still needed lots of chips and chips had big pins so you could 
get a scope probe on them.  My part was to connect scope probes to the 
interrupt line from the ethernet chip and the chip select for the MAC address 
ROM.  He patched the driver's interrupt routine to read the ROM.

These are my opinions.  I hate spam.

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