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10-Apr-85 02:38:32-EST,1551;000000000001
Return-Path: <@COLUMBIA-20.ARPA:MRC@SIMTEL20.ARPA>
Received: from COLUMBIA-20.ARPA by CU20B.ARPA with TCP; Wed 10 Apr 85 02:38:26-EST
Received: from SU-SCORE.ARPA by COLUMBIA-20.ARPA with TCP; Wed 10 Apr 85 02:38:46-EST
Received: from SIMTEL20.ARPA by SU-SCORE.ARPA with TCP; Tue 9 Apr 85 23:29:11-PST
Date: Wed 10 Apr 85 00:28:55-MST
From: Mark Crispin <MRC@SIMTEL20.ARPA>
Subject: IAC doubling: the saga continues
To: TOPS-20@SU-SCORE.ARPA
There have been several messages about a correct
implementation of IAC doubling on TVT's to prevent a binary '377
character being output causing spurious interpretation of network
protocol. Unfortunately, none of the previously published
patches are perfect. Typically, the problems are paths which can
cause a non-doubled '377 to go through or paths which could cause
many '377s to go through.
This solution seems to resolve these problems.
In TTYSRV, rewrite TCOU6 to look like:
TCOU6: CAIE T1,377 ;OUTPUT BYTE = IAC?
JRST TCOU6B
TDCALL D,<<TV,TCOU6A>> ;YES, DO TCOU6A TWICE IF A TVT
JRST TCOU6B
TCOU6A: SAVEAC <T1,T2>
TCOU6B: LOAD 3,TOMAX,(2) ;CAPACITY OF OUTPUT BUFFERS
...etc...
At TCOU5-1, replace JRST TCOU3 with JRST TCOU6B
In TTANDV, rewrite TCOBN to look like:
TCOBN: SAVELN ;SAVE LINE NUMBER
TXZE T1,.LHALF ;WANTS IT LITERALLY?
JRST TCOU6B ;YES, NO IAC DOUBLING PLEASE
ANDI T1,377 ;8 BITS OF CHARACTER
CALL TCOU6 ;GO OUTPUT THE CHARACTER WITHOUT ADDING
; PARITY OR DOING LINKS
RET ;RETURN
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