[time-nuts] Of rubidium life and piggy-bank anemia....

[Bruce Griffiths]

The thorny issues of avoiding the noisy environment of a PC and its
unstable PCI clock whilst still allowing a PC to be synchronised to an
external timebase may perhaps be adressed by:

Producing a simple PCI (or PCIe, or even ISA bus card - still widely
used in industry) board that has a counter clocked by the PCI clock
together with suitable registers used to time tag PCI bus reads etc as
required by the PC software. If the counter rollover occurs at an
approximately 1Hz rate then an optical (or equivalent isolation
technique) can be used to produce an output isolated from the PC which
can be used by an external multichannel high resolution time tagging
instrument to time tag the counter rollover with a stable low noise
timebase.

This avoids compromising the high the performance of the resolution time
tag instrument with the high noise PC environment and its relatively
unstable PCI bus clock whilst still allowing the PC to be synchronised
to a stable and accurate external timebase.

With such a simple board plugged into the PCI (or PCIe , ISA) bus it
should be easy and relatively inexpensive to produce a new one when
moving to PCIe or its successors.
The same external timestamping instrument can then be retained for years
as PC buses come and go.

The potential issue of obsolete communication standards is best
addressed by using a separate board to implement the interface (LAN,
USB, RS232 etc) which can be updated if and when required.

Optical (serial port) or transformer (LAN) isolation can be used to
isolate the timetag device from the noisy PC ground system whilst
permitting communication between the PC and the instrument.

Bruce