Re: NI DAQ-STC support for non-20MHz external timebase

Now that I'm having to synchronize a couple m-series boards myself, and am 
playing around with their externally driven phase-locked-loop reference 
clocks, I'm reconsidering my objections to David MacMahon's scheme of 
specifying an external clock source and its frequency:

https://mail.comedi.org/pipermail/comedi/2006-July/008026.html

I'm thinking now of extending INSN_CONFIG_SET_CLOCK_SRC to take an 
additional (optional) argument that specifies the clock's period in 
nanoseconds.  The specified clock period could be used by the driver to 
support TRIG_TIMER in commands.  Alternately, the user could specify a 
count of master clock ticks using TRIG_COUNT as a scan_begin_src or 
convert_src, for example.

INSN_CONFIG_SET_RTSI_CLOCK_MODE will probably be removed, since all it does 
beyond what INSN_CONFIG_SET_CLOCK_SRC will do is set the rtsi clock as an 
input or output, something that might be done more uniformly with 
INSN_CONFIG_DIO_INPUT and INSN_CONFIG_DIO_OUTPUT and making the rtsi clock 
channel 7 on the rtsi subdevice.

Any comments are welcome.

-- 
Frank