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From: slackey@bbn.com (Stan Lackey)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Why does my program take so long?
Message-ID: <53096@bbn.COM>
Date: 6 Mar 90 21:37:49 GMT
References: <1894@clyde.concordia.ca>
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Reply-To: slackey@BBN.COM (Stan Lackey)
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In article <1894@clyde.concordia.ca> dcfs018@antares.Concordia.CA writes:
>Therefore the question is, why is my 130XE slow by 10%?  Is it due to the
>RAM refresh?
>Does 10% sound right for memory refresh, or is that way too much
>lost time for such a simple operation

A memory refresh every 16 microseconds is common in DRAM systems.  A
refresh typically takes a 200 ns of so period; typically, that 
calcs out to between 1 and 2% of total time.  Now, the 6501 has a 
1MHz cycle, doesn't it?  If the Atari memory is designed to do one 
cycle per microsecond (which it might be), it might take a full
microsecond to do that refresh.  We're up to 1 cycle in 16, or 6.25%
of the time (assuming the 6502 uses the memory bus nearly every cycle, 
which is probably a good assumption).  If the Atari designers were
conservative, they could have set the refresh rate faster than the 
specified minimum, although 1 cycle in 10 seems overly conservative.

Another thought is that refresh could be done in software.  This
seems unlikely; I think we'd know it by now.

Bottom line: Yes, it is possible that your 10% is due to memory refresh.