Interesting IEEE Code in VIC-1112

From: Jim Brain <brain_at_jbrain.com>
Date: Fri, 11 Mar 2016 21:59:58 -0600
Message-ID: <56E3943E.2000407@jbrain.com>
IN this forum post:

http://www.sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?f=2&t=7855

Simon Rowe has disssembled the code in the VIC-1112 adapter.  I think it 
is interesting how much dead code is in the listing:

echkout    jsr fndflno        ; find file
     beq lb0bf        ; branch if file found
     jmp fe_ntopn        ; do file not open error and retirn
lb0bf    jsr setflch        ; set file details from table,X
     lda fa            ; get device number
     bne lb0c9        ; branch if device is not keyboard
     jmp fe_ntout        ; do not output file error and return
lb0c9    cmp #$03        ; compare device number with screen
     beq lb0d2        ; if screen save output device number and exit
     bcs lb0d6        ; branch if > screen, IEEE bus device
     jmp $f321        ; jump to KERNAL to handle RS-232 and tape
lb0d2    sta dflto        ; save output device number
     clc            ; flag ok
     rts
lb0d6    jmp lb0e8        ; skip dead code

     nop            ; *** dead code ***
     jmp $f332        ; *** dead code ***
     cmp #$09        ; *** dead code ***
     bne lb0e8        ; *** dead code ***
     jsr lb59d        ; *** dead code ***
     sta dflto        ; *** dead code ***
     clc            ; *** dead code ***
     rts            ; *** dead code ***

lb0e8    jsr lb40c        ; command an IEEE device to LISTEN
     sta dflto        ; save output device number
     clc            ; flag ok
     rts

The author of the post conjectures that the code was lifted from 
somewhere else, like the PET.  Anyone recognize any of the dead code?

Jim


       Message was sent through the cbm-hackers mailing list
Received on 2016-03-12 05:00:11

Archive generated by hypermail 2.2.0.