Experimental Physics and
Industrial Control System

Rod Nussbaumer <[email protected]> · Thu, 12 Jan 2012 14:10:08 -0800

Hi all.

I've been trying to read waveforms from a Tektronix TDS8000 scope using

R3.14.11 + StreamDevice (2.4) + asyn (4.13) + linux-gpib using a NI PCI

GPIB interface on an x86 PC platform. I cannot seem to find the right

message termination to satisfy all of the various components.

The scope documentation says it does not use end-of-line terminator

characters, but rather sets EOI on the GPIB to signal end of messages.

Nevertheless, there are LF characters appended to each message, even

binary formatted waveform data. I'm trying to use RIB encoded

(Intel-endian binary) waveform data, 4-byte words.

I'm hoping to read 10 waveforms per second on a periodic scan of an

EPICS waveform record, (500 integer data points).

A simple bit of C code is able to read waveforms at about 80 waveforms

per second in a tight loop. In there, I have used the 'ibeos()' function

to cause my C code to not terminate reads on any character delimiters,

and this seems to have the desired effect. In the gpib.conf file, I've

include the setting:

set-reos = no

There is also the setting...

eos = ___

 ... which I've set to 0x0, commented out completely, and set to

0x0a, none of which seems to change anything, and which is in accordance

with my expectation.

Most/some of the settings in gpib.conf seem to correspond to the

capabilities of the asynSetOption() function which I've also used in the

EPICS startup script. There, it does seem to make a difference. If I set...

asynSetOption("GPIB0",10,0x0c,0)
...then asynTrace shows me that it does two things:
   1. terminates its sequential reads on each binary zero byte
   2. times out at the end of the read (and sees/reads the trailing LF)

I seem to be stuck between a rock and a hard place: either I use an

end-of-line terminator, which will eventually show up in the binary data

and prematurely terminate the read, or if I try to use the option to not

use end-of-message characters, it will wait until the read times out,

which seems to have the effect of invalidating the record, and slowing

things down a lot.

Any hints on how to proceed, tests to make or requests for further info

are welcomed.

Thanks.

Rod Nussbaumer
ISAC Controls, TRIUMF
Vancouver, Canada.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System