NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/sys/mac/programm/18570

Internet Message Format | 1992-11-17 | 1.9 KB

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Newsgroups: comp.sys.mac.programmer
Subject: Re: Fixing Apples serial drivers. How?
Message-ID: <[e-mail]>
From: [e-mail]
Date: Wed, 18 Nov 1992 02:20:53 GMT
Sender: [e-mail] (USENET News System)
Organization: VAX Cluster, Computer Centre, La Trobe University
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Here is some more background on my serial driver.

The serial driver on the micro I have been talking to at 38400 baud
is interrupt driven with recieve and transmit buffer $80 in size.
The current implementation of this sends an xoff for every character recieved
that fills the buffer behond a certain size. I have looked into this
driver very thoroughly. It does have some potential problems which I fixed
to do with the interrupt routine stealing the xoff which was a polled
routine within the recieve interrupt handler. Fixing other potential
problems similar to this appeared to have very little effect.

I eventually got the thing working properly by changing the character
limit to a higher value ($30->$70) so that the xoff is sent when the buffer
has a lot more characters in it. The person who wrote the serial handler
for the micro was trying to solve what may have been another proble
by setting the character limit so low. The mac plus can now send the
data without artificial delays being inserted.

So why doesn't it work with such a small buffer size??? My hypothesis is
that the Mac ends up recieving twice as many characters as it is sending.
That is each echoed character plus an xoff. The recieve interrupt on the
mac has a higher priorty than the transmit. Could it be that the transmit
buffer on the mac is overflowing???


Thanks for everones contributions

Richard Rothwell