Re: Out of order replies from a serial device

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hi,

In StreamDevice, I do a pasynOctet->flush(pvtOctet, pasynUser) before doing any 
writes to get rid of "old" replies. Asyn is not doing this automatically (and 
also should not).

The flush() function works as if you do read() until no further data is 
available and discards everything. But it might be significantly faster.

Dirk

Phillip Sorensen wrote:
> Phillip Sorensen wrote:
>
> I took some time to look at the asyn code this morning.  I am looking at 
> ASYN 4-6.
>
> > Mark Rivers wrote:
> >
> > > I believe asyn is doing the flush operation that Emmanuel suggested.
>
> As far as I can tell, there is no flush before writes at either the 
> devGpib level or the port driver level for drvAsynSerialPort or 
> drvAsynIPPort.  What I did find was that in the drvAsynSerialPort.c file 
> that a timeout at this level causes a flush.  There is no similiar flush 
> in the drvAsynIPPort.c code.
>
> > > I suspect you are not getting out of order replies.  I think you are 
> > > getting a timeout, but then stale data from some buffer is ending up 
> > > in the apparent data you received with the timeout. 
>
>
> The "out of order" data seems to be coming from the OS socket buffer (I 
> am running under linux).  They are never flushed after a timeout.
>
> This looks like a "possible" bug to me, and think that flushing the 
> buffer would do away with my "out of order error", BUT I don't think it 
> is the root cause of my problem.
>
> After taking a second look at the code, I think I have found the root of 
> my problem.  I was puzzled by the fact that the code seemed to work with 
> an older version of ASYN and that increasing the timeout parameter had 
> no effect on the problem.
>
> It appears that when the timeout handling code was removed from the 
> drvAsynIPPort driver the SOCK_EINTR error return from the recv is now 
> treated as if it were a timeout.  In the previous version of the code 
> that I have and in the drvAsynSerialPort code, the recv was inside a 
> for(;;) loop which would retry the read in the EINTR error state.
>
> I will try to put together a patch to retry to the recv on SOCK_EINTR in 
> the next day or so.
>
>
> Phil Sorensen
> CHESS

--
Dr. Dirk Zimoch
Swiss Light Source
Computing and Controls
Paul Scherrer Institut
phone +41 56 310 5182
fax   +41 56 310 4413