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From: awanderin <awanderin@gmail.com>
Newsgroups: comp.sys.apple2.programmer
Subject: Re: Can anyone see a way to improve this ?
Date: Mon, 27 Oct 2014 21:35:29 -0600
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mdj <mdj.mdj@gmail.com> writes:

> Hi,
>
> Below is a memory test loop for 1 page - assume the high order bytes
> get replaced for each page being tested. Zero page is deliberately
> avoided - this runs in either the language card or the $800-$BFFF area
> of main memory, testing pages of auxiliary memory without assuming any
> given byte of aux memory works.
>
> The obvious one is to unroll, which I'll do. Just wondering if I'm
> missing something else obvious.
>
> Thanks,
>
> Matt
>
>
>          LDX   #$00
> NEXTBYTE LDY   #$08
>          LDA   #$01
> NEXTBIT  EOR   #$FF       ; Set and check complement first
>          STA   $2000,X
>          CMP   $2000,X
>          BNE   ERROR
>          EOR   #$FF
>          STA   $2000,X
>          CMP   $2000,X
>          BEQ   CONT
> ERROR    JSR   FLAGERR
> CONT     ASL
>          DEY
>          BNE   NEXTBIT
>          INX
>          BNE   NEXTBYTE
>          RTS
> FLAGERR  RTS              ; Record this meaningfully in the future
>
>
>

For a thorough discussion of strong memory-checkers, see this article:

    http://www.ganssle.com/articles/ramtest.htm

I guess it depends on how confident you are in the machine's RAM in the
first place.

--
Jerry    awanderin at gmail dot com