No-vxworks DAQ and Linux interrupt latency (fwd)

[Elton Smith <elton@jlab.org>]

---------- Forwarded message ----------
Date: Thu, 27 Apr 2000 14:10:22 -0400
From: Elliott Wolin <wolin@jlab.org>
To: Don Holmgren <djholm@fnal.gov>, Don Petravick <petravick@fnal.gov>
Cc: Vardan Gurjyan <gurjyan@jlab.org>, elton@jlab.org
Subject: No-vxworks DAQ and Linux interrupt latency

Dear Dons,

Haven't seen you folks in a while...perhaps we'll meet at the next Real-Time
conference, if they feel rich enough here to send me.

Anyway, I've been thinking about no-vxworks DAQ systems. 

We've had success reading vme modules into a linux box via a SBS-Bit3 model 617
pci-vme bridge.  Could I eliminate the ppc in the vme crate and use the 617
instead? Problem is interrupt latency.  

Alternatively, I could use vme dual-port memories with built-in dma engines and
sequencers to move the data out of the front ends into the dual-ports, then read
out the dual-ports at my leisure.

I seem to recall you modified the linux kernel to speed up interrupts...what's
the latest on this?  Is real-time linux anywhere near available?   What is it's
interrupt latency?  Is it limited by pci?

Anyone doing daq this way you know of?

I'm mainly thinking about this for the proposed Hall D experiment (exotic meson
production search...i.e. very high precision search for gluonic excitations
using fancy partial wave analysis) at JLab...at least a few years off.  But also
for upgrades to existing detectors...might be able to eliminate vxworks and have
no cpu's locked away in radiation areas.

Any ideas, leads, names, etc. would be appreciated.


				Sincerely,
					Elliott
 

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