From ripley@stats.ox.ac.uk  Wed Jun 19 10:15:41 2002
From: ripley@stats.ox.ac.uk (ripley@stats.ox.ac.uk)
Date: Wed, 19 Jun 2002 11:15:41 +0200 (MET DST)
Subject: Maybe a problem in binary read/write (PR#1688)
Message-ID: <200206190915.LAA29641@pubhealth.ku.dk>

Not a bug: check the documentation of file(), which is documented to work
for files but not for devices.  No attempt is made to cope with e.g.
blocking on non-files.

It's a pretty extreme view of the world to consider /dev/psaux to be a
file, and R is just using standard C <stdio.h> I/O.

However, this is a great opportunity for you to contribute a device()
function to R.

On Tue, 18 Jun 2002 accot@free.fr wrote:

> Full_Name: Johnny Accot
> Version: 1.5.1
> OS: Linux
> Submission from: (NULL) (198.4.83.52)
>
>
> Hi.
>
> I'm having a problem with the binary read/write functions.  I'm writing a device
> driver in R (why not?) and of course I have to send a couple commands to the
> device.  Typically, I send one byte, receive one acknowledgement byte, send
> another byte, receive an ACK, and so on.  At least this is what I would like to
> do.  Instead, after writing one byte, reading its acknowledgement byte, and
> writing a second byte, R hangs on the next read for an unknown reason.  I guess
> this is a bug in the read/write functions.  If you have a PS/2 device you may
> try to run the following code:
>
> ascii <- sapply(1:255, function(i)
> parse(text=paste("\"\\",structure(i,class="octmode"),"\"",sep=""))[[1]])
> dev <- file("/dev/psaux")
> open(dev, "w+b")
> writeChar(ascii[246], dev, eos=NULL)
> readBin(dev, what=integer(), n=1, size=1, signed=FALSE)
> writeChar(ascii[246], dev, eos=NULL)
> readBin(dev, what=integer(), n=1, size=1, signed=FALSE)
> close(dev)
>
> which gives:
>
> > ascii <- sapply(1:255, function(i)
> parse(text=paste("\"\\",structure(i,class="octmode"),"\"",sep=""))[[1]])
> > dev <- file("/dev/psaux")
> > open(dev, "w+b")
> > writeChar(ascii[246], dev, eos=NULL)
> > readBin(dev, what=integer(), n=1, size=1, signed=FALSE)
> [1] 250
> > writeChar(ascii[246], dev, eos=NULL)
> > readBin(dev, what=integer(), n=1, size=1, signed=FALSE)
> [...R hangs here...]
>
> It first creates an ascii table, opens the PS/2 device for binary read&write,
> writes the byte 0xF6 (246 in decimal, which means: set default; it is harmless),
> reads the acknowledgement byte 0xFA (250 in decimal), writes another 0xF6, and
> then hangs when reading the second acknowledgement byte.  If, instead, you close
> the device between the two writes, it's fine:
>
> > ascii <- sapply(1:255, function(i)
> parse(text=paste("\"\\",structure(i,class="octmode"),"\"",sep=""))[[1]])
> >
> > dev <- file("/dev/psaux", "w+b")
> > writeChar(ascii[246], dev, eos=NULL)
> > readBin(dev, what=integer(), n=1, size=1, signed=FALSE)
> [1] 250
> > close(dev)
> >
> > dev <- file("/dev/psaux", "w+b")
> > writeChar(ascii[246], dev, eos=NULL)
> > readBin(dev, what=integer(), n=1, size=1, signed=FALSE)
> [1] 250
> > close(dev)
>
> This is not a feature, is it? :-)  The behavior is the same in versions 1.4.1,
> 1.5.0 and 1.5.1 on my computer.  I don't have to send bytes very often, so I'll
> stick with the open-each-time strategy, but it is not very clean.
>
> I also tried to write bytes using the writeBin command, but it says the "size=1"
> is not available on my computer.  This is why I'm using the writeChar function.
>
> Please let me know if I'm doing something wrong.  I hope not.
>
> And thanks for the great software! :-)
>
> Johnny
>
> PS: if you try to run the code and don't get 250 as acknowledgement byte, it
> means the PS/2 controller is not in idle state.  Very unlikely though.  Try
> again as the set-default command should bring it back to its idle state.
>
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-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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Maybe a problem in binary read/write (PR#1688)
ripley@stats.ox.ac.uk