[Halld-cal] Draft f250 data words for comments

[Alexander Somov]

Hi Elton,

I see two problems with the proposed format:

- pedestals (and channel numbers) will be reported
multiple times for multiple pulses in  the readout
window.

- when we read out the pulse integral only (suppress
time information). The pulse time in the readout
window is not reported. The pulse time is essential
as it has to be correlated with the trigger time
(for the tagger, for instance).

It is more logical to separate the integral and
time information in two words. We can still stay
with 3 words per single pulse but will not multiply
words for multiple pulses.

Below is the proposed format:


Reported once per channel with hits.
(31)    = 1
(30-27) = Data type
(26-23) = channel number (0-15)
(16-22) = pedestal width used in the sum
(15-0)  = pedestal sum

Reported multiple times for each individual pulse (if needed)
(31)    = 0
(30)    = 1  Integral
(27-29) = quality
           (bit 0 - underflow used,
            bit 1 - overflow used,
            bit 2 - truncated by readout window)
(19-26) = coarse time (8 bits)
(18-0)  = pulse integral

(31)    = 0
(30)    = 0  Time
(29-21) = coarse time (9 bits)
(20-15) = fine time (6 bits)
(14-12) = quality factor (3 bits)
(11-0)  = pulse peak (12 bits)


The event number and the trigger time can be combined in the
event header (though I would not suppress event headers from
the boards for events with no hits, it can be done on the second
readout list).

We have a few more specs on the fadc250. I'll update the doc
(for scint detectors) shortly.

Cheers,
       Alex






On Tue, 21 Jul 2015, Elton Smith wrote:

> Dear colleagues,
>
> We have been discussing various considerations for the next f250 firmware 
> upgrade. Based on the size of the spring data with mode 7, we see that the 
> data volume is dominated by header words and not the "content" per se. 
> Therefore, it appears that we should be able to handle the GlueX rate with 3 
> words for the calorimeter "content". However, it would be desirable to 
> separate the pedestal into one word, which could be dropped if size becomes 
> an issue. Attached is a draft scheme for discussion that achieves these 
> goals.
>
> Feedback is welcome.
>
> Cheers, Elton.
>
> -- 
> Elton Smith
> Jefferson Lab MS 12H3
> 12000 Jefferson Ave STE 4
> Newport News, VA 23606
> (757) 269-7625
> (757) 269-6331 fax
>
>