Re: Reading scope waveforms with StreamDevice + asyn

[Rod Nussbaumer <bomr@triumf.ca>]

Thanks, Dirk.

I have observed the 64-byte reads often in the past, and wondered 
whether there was a way to increase that amount, for purposes of 
efficiency. In this case, I do know the size of the array I expect to 
read, as it is a fixed size, and each binary word is the same, plus some 
accompanying header data, also of fixed length and makeup.
I am reading/matching the trailing LF. I wasn't sure whether setting
InTerminator = ""
is the same as not setting it explicitly at all, or whether it might 
cause it to take on some new meaning. I do know that each protocol can 
have specific terminator settings, and I've been trying to use that in 
various combinations. What is the expected behavior if no Terminator or 
InTerminator is specified, neither globally within the protocol file, 
nor in the specific protocol? What I'm seeing in that case appears that 
any NULL byte terminates a read. This causes a huge number of short 
reads per waveform.
> 2012/01/13 08:50:10.847 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.847 GPIB0 addr 10 gpibPortRead
> $
>
> 24 00
> 2012/01/13 08:50:10.857 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.857 GPIB0 addr 10 gpibPortRead
>
>
> 00
> 2012/01/13 08:50:10.868 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.868 GPIB0 addr 10 gpibPortRead
>
>
> 00
> 2012/01/13 08:50:10.878 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.878 GPIB0 addr 10 gpibPortRead
> P
>
> 50 00
> 2012/01/13 08:50:10.888 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.889 GPIB0 addr 10 gpibPortRead
>
>
> 00
> 2012/01/13 08:50:10.899 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.899 GPIB0 addr 10 gpibPortRead
>
>
>
> 0a
> 2012/01/13 08:50:10.909 GPIB0 addr 10 gpibRead
> 2012/01/13 08:50:10.929 GPIB0 addr 10 : device timed out.
>
> epics>
If I set InTerminator="" in the protocol, the same thing happens, but I 
also get, at the end of the record processing:
> 00
> 2012/01/13 08:54:42.269 GPIB0 addr 10 gpibRead
> 2012/01/13 08:54:42.269 GPIB0 addr 10 gpibPortRead
>
>
>
> 0a
> 2012/01/13 08:54:42.279 GPIB0 addr 10 gpibRead
> 2012/01/13 08:54:42.299 GPIB0 addr 10 : device timed out.
> 2012/01/13 08:54:42.299 GPIB0 addr 10 setEos eoslen 0
Note the reference to EOS in the last asyn message. I sense that this is 
germane to the problem.
I am a bit curious about *how* terminators are used/implemented in 
streamDevice. Does the recognition of terminators get used only within 
streamDevice, or does it get passed down to asyn in some way? To me, 
there are different purposes to the terminators, especially in the case 
of GPIB, where the low level drivers have their own behaviors for 
message termination. It seems that there may be some interplay that is 
hidden.
So far I think I've determined (from code inspections in the asyn linux 
GPIB port driver) that the behavior of asyn plus the asynSetOptions() 
I'm using should be mimicking my own test/diagnostic C code. I wonder 
whether streamDevice is asserting some communication options through its 
use of asyn? I will start looking into the streamDevice code, but if 
anyone knows for sure, I would be happy to hear.
Mark, I haven't tried the asyn record tests yet, as I'm not really 
familiar with how to implement and use it, but now is looking like a 
good time learn.
Thanks.

   ---   rod.




Dirk Zimoch wrote:
> Hi Rod,
>
> If everything works correctly in asyn, it sees the EOI and tells
> StreamDevice that this is the end of the message via the (eomReason &
> ASYN_EOM_END) bit (in opposite to the ASYN_EOM_EOS bit when a terminator
> is found). So it should work with an empty terminator.
>
> I guess you know that you can set the terminators individually for each
> protocol. So ASCII protocols can use LF and binary protocols "". In
> order to get rid of the LF at the end of the message, you have to read
> it in the protocol after reading the array. The waveform record reads
> data until either NELM elements are read or the message ends. If the
> array has variable size, you need to set NELM large enough. When trying
> to read the next 4-byte word, StreamDevice will find at some point that
> only one byte is left and stop reading. That byte (LF) will stay in the
> input and you have to read it explicitly.
>
> However, StreamDevice has one problem with GPIB but I don't know if it
> affects you: The asynGpib implementation (at least for vxi11, the only
> one I can test) does not allow to read the message in chunks. One has to
> know in advance how long the message is and need to provide a
> sufficiently large buffer. Therefore, StreamDevice starts with a 64 byte
> buffer for GPIB devices. This is enough for most messages but not for
> arrays. If the buffer is too small and the message cannot be read in
> chunks, asyn should return a asynOverflow error. In that case,
> StreamDevice increases the buffer size by doubling it. But this
> transmission fails. One of the next transmissions may succeed as soon as
> the buffer is sufficiently large.
>
> This problem may be fixed in a future version of asyn or may even have
> been fixed without me noticing it. One workaround would be to add a
> variable to StreamDevice to specify the initial buffer size.
>
> I have no idea how linux-gpib behaves. I can only test vxi11.
>
> Gruss
> Dirk
>
> Rod Nussbaumer wrote:
> > 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.