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From: daveb@cbmvax.cbm.UUCP (Dave Berezowski)
Newsgroups: net.micro.amiga
Subject: Re: Sending multiple chars out the serial port
Message-ID: <669@cbmvax.cbmvax.cbm.UUCP>
Date: Thu, 21-Aug-86 20:52:31 EDT
Article-I.D.: cbmvax.669
Posted: Thu Aug 21 20:52:31 1986
Date-Received: Fri, 22-Aug-86 20:59:36 EDT
References: <903@batcomputer.TN.CORNELL.EDU>
Organization: Commodore Technology, West Chester, PA
Lines: 50

> WriteSer(io,data,length)
> struct IOExtSer *io;
> char *data;
> int length;
> {
> 	io->IOSer.io_Data = (APTR)data;		/* Abridged version */
> 	io->IOSer.io_Length = length;		/* to speed typing */
> 	io->IOSer.io_Command = CMD_WRITE;
> 	return(DoIO(io));
> }
> 
> Ok, this function works perfectly if "length = 1", ie if you are only
> writing one character out the port.  However, if we are writing a
> known length string out the port, say "char data[5] = {'h','e','l','l','o'} "
> and we give data = &data[0] and length = 5, then we get maybe the
> first two characters received by the serial listener fine, but the rest
> is random garbage chars.  By the way, this occurs at Baud rates as slow
> as 300, and with parity, stop bits, write bits identical on both ends
> of the serial port.  At first I thought it was overwriting an output
> buffer, but I guess "data" points to the output buffer.  So we can't
> figure out why we can't send the string.
>    Our temporary solution has been to do a for loop and just send each
> individual char out with length = 1; this works fine.  But this is
> not very nice at high bauds, so if anyone has any clues as to our 
> problem, it would be appreciated.
>    Note that this symptom appeared in Workbench v1.1.  We upgraded to
> V1.2 beta 4 recently, but the problem still persists.
> 
> Thanks much, 
> -- JR
> UUCP: ihnp4!cornell!batcomputer!dyon
> ARPA: dyon%batcomputer@cu-arpa.ccs.cornell.edu

	The above code should work verbatum. HOWEVER, if you are using 
SendIO instead of DoIO then LET THE BUYER BEWARE! If you call an
asynchronous routine like SendIO for the serial port then you must
assume that it owns the variables you pass to it until it has
completed NOT neccessarily when it returns from the call. In this
case you are passing a pointer to your data. If you alter the pointer
OR change the data in the buffer before the serial device is finished
sending it, you'll get garbage chars. I had this bug and fixed it by
copying the data to a local buffer before doing the SendIO so that I
could use my other vars while the chars were being sent out.

	I know that I didn't answer your question directly but I wanted
to give you some insight into what would happen if you ever use SendIO.

	Hope you find your bug!

	Regards, David Berezowski.