Timestamp options for SGIR.

The SGIR controller no internal clock. In order to timestamp images, the IRTF can
toggle the SGIR's Shutter output just before starting an integration. This 
pulsed can be timestamped by a computer. Two methods to timestamp this
shutter pulse is discussed:
   1. Parallel Port
   2. GPS Board.

Each controller computer would need to timestamp the image. Thus 6 computers:
   sgir, nsfcam2, spex bigdog & guidedog, ishell spectrograph & slit viewer.


1. Parallel Port method 

It may be possible connect the shutter to the PC's parallel port, and the PC could 
timestamp the shutter. The expected resolution would be 5-10 microseconds.
Hardware cost is 0 (every PC _should_ has a parallel port).

2. GPS board method.

A GPS PCI board can purchased and used to timestamp the shutter TTL.
Many GPS boards can timestamp external events using a TTL input. 
The accuracy of the time stamp is about 100 nanoseconds.
These PCI board computer in 2 flavors:

    1. GPS Board: boards that sync using a GPS antenna. Cost is about $3.5K.
    2. Timer Board: boards that sync using a time code signal (such as IRIG A/B). 
        Cost is about 1.5K.
   
Since the IRTF has a GPS with time code output, type 2 could be used.
How to distribute the IRIG code could be an issue, as 5 computers would be used.
In total we would need:
      sgir: GPS board, $3.5K
   nsfcam2: Timer board, 1.5K
      spex: 2 Timer boards, 1.5K x 2
    ishell: 2 Timer boards, 1.5K x 2
    With every system having a timer board, a TimeCode repeater may be needed to 
    distribute the time code. 

Vendor GPS boards:

       VENDOR           MODEL   Trig/buffer  IRIG_In   IRIG_OUT   GPS_IN    COST
   www.symmetricom.com  bc635PCIe  3        yes        yes       no       1300     
                        bc637PCIe  3        yes        yes       yes      2500 (includes GPS 50ft cable)
									  +900 (amp + 250ft cable)	


   www.meinberg.de      TCR170PEX  2/500     yes       B only    no       1200
                        GPS17PEX   2/500     no(?)     B only    yes      2300 (includes GPS)
References:

Symmetricom web site - vendor's web site.
	ds_bc635pcie.pdf - data sheet for timer board.
	ds_bc637pcie.pdf - data sheet for GPS board.
	BC635_637PCIeUserGuide_RevA.pdf - user guide.
	PCI_LinuxSDK_0808.pdf - Linux SDK document.

www.meinberg.de - vendor's site.
	gps170pex.pdf - gps board info.
	tcr170pex.pdf - timer board info.