Re: Accomodating I2C and CAN in Hall D control system

[Gerard Visser <gvisser@indiana.edu>]

Hall D Electronics:

Hi Elliott,
	It should be noted that _all_ control functions for the ADC125 are done 
by VME. I presume the same is true of the ADC250 and the F1TDC boards 
(Fernando?).
	For the ADC125, I think there are three types of control/monitoring 
functions.
	A. Readout controls to setup, e.g., latency setting, window length, 
zero suppression thresholds, probably some time/amplitude algorithm 
parameters, channel masks, etc. This stuff, I imagine you should 
download once at the start of a run and no need to touch them during a 
run. So this is no bandwidth burden on the DAQ system.
	B. A few housekeeping parameters to read and log and/or alarm on. This 
means, most importantly, board temperatures, probably some power supply 
voltages/currents. These things are read only and expected to vary. They 
need be read at most once every couple of seconds, and no need to read 
synchronously across different boards. It seems to me this should not be 
a big burden.
	C. Scalers and other data monitoring, e.g., storing min/max/mean values 
(if you want any scalers or such stuff). I would imagine there should be 
at least one simple level crossing scaler per channel. Probably more, 
e.g., count pulses going over 95% full scale, so you know what is 
getting saturated. I have already proposed to you that a separate 
trigger command is defined to cause all ADC125 boards to simultaneously 
capture their scaler data and stuff it as a special "event" packet into 
the DAQ stream. In this way the readout of scalers proceeds at maximum 
speed with a minimum of effort from front end through to online display 
software (I think), and also it is, I would imagine, useful to have them 
captured simultaneously. If this is not a good plan, for whatever 
reason, vanilla VME transactions may be used to capture and read the 
scaler data. Or you can tell me not to include any scalers at all. (Well 
I probably would do so anyway to facilitate testing, but you wouldn't 
have to read them of course.)
	Besides the fact that I don't want to have any I2C or such control 
interface into the ADC125, I don't think it would be at all appropriate 
for item C. And item C would presumably account for the greatest part of 
the controls bandwidth for these boards.
	Comments? Asap if there are significant objections to the above...

	- Gerard

Elliott Wolin wrote:
> Hall D Electronics:
> 
> Dear Gerard, Fernando, and friends,
> 
> I understand there will be a large number of I2C and CAN channels in Hall D.  In
> particular, one I2C channel per 24-channel preamp card, and one CAN channel per
> Cockroft-Walton base.  I understand there are other I2C channels (how many?);  are there
> additional CAN channels?
> 
> I don't know how many I2C and CAN channels can be daisy-chained on one I2C or CAN bus.  We
> may not want to daisy-chain too many channels, as then access to each device might take
> too long, e.g. when setting all the C-W high voltages prior to starting a run.
> 
> Further, I assume the detector and/or electronics budgets include whatever devices are
> needed to read out I2C and CAN, as the online budget contains just computers and network
> components.
> 
> Finally, I am concerned about mixing controls and DAQ data paths.  How are all the I2C
> devices connected and read out?  I hope not via VME in the DAQ crates, as this would
> interfere with the high-speed DAQ readout.
> 
> Controls data paths should be independent of DAQ data paths unless the controls data is
> intimately associated with DAQ (e.g. trigger scalers), i.e. only needed if DAQ is running.
> 
> Thanks,
> 
>                                 Sincerely,
>                                         Elliott
> 
> 
> ================================================================================
> 
> 
>   Those raised in a morally relative or neutral environment will hold
>                     no truths to be self-evident.
> 
> 
> Elliott Wolin
> Staff Physicist, Jefferson Lab
> 12000 Jefferson Ave
> Suite 8 MS 12A1
> Newport News, VA 23606
> 757-269-7365
> 
> ================================================================================