Implement startex and readex commands for separating functions in expose command

[scizen9]

Specifically for DEIMOS, we need to initiate a science integration and then switch taps to to the FCS detector. The current 'expose' command will initiate, wait for expose, then wait for readout all in one command. We need to separate the initiate exposure from the wait for readout command.

Hopefully, this can be implemented in such a way as to be generally useful.

[astronomerdave]

Currently the expose command initiates the exposure and then goes into readout. We leave the existing expose command and add the two new commands which break that up into the two separate steps,

• startex (which means "expose no read")
• readex (which means read, but read what, exactly?)

There probably will need to be a configurable parameter for the startex command in the same way there is a configurable parameter for expose (I.E. the expose command writes Expose=1 to the Archon, where the Expose parameter is configurable). This would allow the Archon to take any unique steps such as not automatically running the readout waveforms.

Likewise, the readex command would need a configurable parameter in order to trigger the appropriate waveforms to read the exposure that was triggered with startex.

Something like this would enable the camera interface to remain both generalized and backwards compatible.

[scizen9]

If we can get a hold of the WASP ACF file, we can see how this functionality was implemented in that ACF. WASP has three detectors (focus, guide, science) controlled by one archon, so we know that the triggering of integration separately from readout must have been implemented in the WASP ACF.