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From: jprad@faatcrl.UUCP (Jack Radigan)
Newsgroups: comp.sys.amiga.datacomm
Subject: Re: XON/XOFF flow control (was re: 19200 baud amiga)
Message-ID: <1057@faatcrl.UUCP>
Date: 5 Mar 91 14:48:00 GMT
References: <1047@faatcrl.UUCP> <26673@netcom.COM> <1051@faatcrl.UUCP> <26918@netcom.COM>
Organization: FAA Technical Center, Atlantic City NJ
Lines: 24

gandrews@netcom.COM (Greg Andrews) writes:

>This still sounds wrong to me.  The XOFF is sent to the transmitting
>computer at the faster speed also.  It should be recognized in time
>to halt transmission only a couple of characters later.  If the
>receiving computer didn't react quickly (sending the XOFF), or the
>transmitting computer didn't react quickly (recognizing the XOFF and
>pausing transmission), then you could get an overflowed buffer only
>at high speeds.

  Being sent at a faster rate leaves less time for the cpu to react to the
XOFF, so more data slips past before the device stops sending data.

>Another possibility is that the thresholds for RTS/CTS handshaking
>and XON/XOFF flow control are the same, and don't leave much room
>for overruns.  Since XON/XOFF is a 'slower' method of flow control
>(meaning more characters can come in before the flow stops), the
>threshold for XON/XOFF should be lower than that for RTS/CTS.

  Normally, CTS/RTS is hardware controlled and XON/XOFF is software
controlled.  On the Amiga, both are software controlled.  So, a different
value must be used for each method since I see data loss with XON/XOFF and
not CTS/RTS.

  -jack-