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Francesco reminded me of another readout issue we have to solve. His
message is included here:
> The maximum size for an event allowed from the current acquisition is
> 64 kbytes for each microVAX. (I have told you many times!). It is
> difficult to increase a large amount (maybe a factor of 2 could be
> possible perhaps) due to a lack of memory available in the KAV-30 and
> in the host computer. Moreover the dead time is dependent from the
> maximum buffer size. Generally all the acquisition performances are
> dependent (because the time necessary to allocate large buffers is
> bigger than the time for smaller buffers). In any case with the
> current acquisition for large buffer transfer bigger than 64 kbytes
> you should have errors due to the memory allocation.
So this is something for us to look into. It sounds like the daq is
allocating memory on an event by event basis. I find this surprising; it
should be possible to preallocate all the memory needed for the largest
"possible" event. But I haven't looked through the system to see exactly
how this is implemented. In any case- this is a real problem that needs
a solution. I estimated that a full SM of data (slow monopole candidate)
would occupy 200 kbytes (just the waveform data).
There is another memory limitation that we must solve. The VME-VMV
interface of the VIC-8250 maps the absolute addresses of the slave crate
(wfd) into a 1 Mbyte window. However each crate has at least 3 Mbytes
of memory (4:1 fanin => 12 cards at 4 channels/card x 64 kB/channel).
This is the way the uVaX/VIC software and hardware are set up now. But
this will not cut it in the future. The VIC-8250 data sheet and manual
also report a capability to set up a 16 Mbyte window using the VSB slave
interface. We should try to set this up now before we commit to more DAQ
hardware.
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I have set up a directory: [MACROUSA.WFDINFO] on VAXGS:: to be a
repository for miscellaneous wfd files that might be useful or
informative. It now contains these updates, some c code for playing with
the front-end amp, text files describing bits and pieces of the system
and so on.
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