From accot@free.fr  Tue Jun 18 21:51:18 2002
From: accot@free.fr (accot@free.fr)
Date: Tue, 18 Jun 2002 22:51:18 +0200 (MET DST)
Subject: Maybe a problem in binary read/write (PR#1688)
Message-ID: <200206182051.WAA26484@pubhealth.ku.dk>

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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Maybe a problem in binary read/write (PR#1688)
accot@free.fr