Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!kddlab!atrpost!atr-la!alain
From: alain@atr-la.atr.co.jp (Alain de Cheveigne)
Newsgroups: comp.sys.mac.programmer
Subject: Re: FSRead hangs on the serial driver
Message-ID: <3915@atr-la.atr.co.jp>
Date: 11 Jan 90 08:24:59 GMT
References: <7770@unix.SRI.COM> <4713@hydra.gatech.EDU <6113@internal.Apple.COM>
Organization: ATR International,Japan
Lines: 27
In-reply-to: chesley@goofy.apple.com's message of 11 Jan 90 01:26:52 GMT


In article <6113@internal.Apple.COM>, chesley@goofy.apple.com (Harry
Chesley)writes: 

>The default input buffer for the serial port is only 64 bytes. 
>So 80 characters can easily overflow the buffer if you don't read it out 
>fast. You can increase the buffer size by calling SerSetBuf (but be sure 
>and unset the buffer by calling SerSetBuf with a length of zero before 
>exiting the application or you'll get horrible crashes).

I currently use a 8172 byte buffer, and I don't unset the buffer on 
exit.  I have never witnessed such a crash.

While the subject is up: even with a 8172 byte buffer I sometimes lose
characters.  It seems that the ethernet pad I'm connected to takes too
long to react to an XOFF.  

The question is: at what point does the serial driver send the XOFF?
When a given *proportion* of the buffer is full?  Or when the buffer
is a given *number of bytes* from being full?

If it is the latter, making the buffer bigger only reduces (slightly) 
the probability of losing characters.


Alain de Cheveigne,
alain@atr-la.atr.co.jp