Experimental Physics and
Industrial Control System

Zenon Szalata <[email protected]> · Fri, 11 Oct 2013 13:33:39 -0700

Hi Mark,

I have written a device driver for a GPIB device that is using VXI11

protocol.

The device driver is sub-classed from the asynPortDriver class.
In the st.cmd file I configure the VXI11 object as follows:
vxi11Configure( "L0x","$(ETHER)",0,0.0,"gpib0",0,0)

Then in the constructor I connect:

stat=pasynOctetSyncIO->connect( _ioPort,_addr,&_apvt,0);

finally in IO routine I call:

stat=pasynOctetSyncIO->writeRead(

_apvt,pcs,ncb,_buf,nbt,1,(size_t*)nio,&nbi,&eom);

_buf is defined as char _buf[2048]

I have discovered by trial and error that the writeRead succeeds for nbt

<= 32 and fails otherwise.

I do not understand this. I think that nbt is supposed to be the size

of the read buffer (in my case _buf) simply telling the routine, which

ultimately does the device IO, to put up to nbt bytes of data into the

read buffer. Now, it happens that in my test case the device returns

only one byte of data, that is the status byte. So, why should it fail

when I give the writeRead a ridiculously large buffer to read into?

Then what if I poke the device and it chooses to reply by sending 1024

bytes of data? Do I need to worry about that and issue the writeRead

number of times with 32 byte long read buffer until all bytes of data

are read in? Since I don't know before hand how much data will be

returned, it is not obvious to me how this could be done efficiently.

Thanks Mark,
Zen

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System