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From: usenet@orstcs.CS.ORST.EDU (Usenet programs owner)
Newsgroups: comp.sys.apple
Subject: Re: Really small question
Message-ID: <14552@orstcs.CS.ORST.EDU>
Date: 27 Dec 89 08:03:39 GMT
References: <kZTLjCG00WB7Q=4bJa@andrew.cmu.edu> <9542@microsoft.UUCP> <742@batman.moravian.EDU> <10071@microsoft.UUCP>
Reply-To: throoph@jacobs.CS.ORST.EDU.UUCP (Henry Throop)
Organization: Oregon State University, Corvallis
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Keywords: 
From: throoph@jacobs.CS.ORST.EDU (Henry Throop)
Path: jacobs.CS.ORST.EDU!throoph

In article <10071@microsoft.UUCP> brianw@microsoft.UUCP (Brian WILLOUGHBY) writes:
<nicholaA@batman.moravian.EDU (Andy Nicholas) writes:
<>I thought the cycle times on MVN/MVP were 7 cycles per byte moved.  How
<>is that as fast as DMA which is supposed to be (at least what I've always
<>been told) 1 cycle per byte moved?
<
<Have you compared the speeds in an actual coding situation?
<

[...]
<
<I believe that you have *graphics* gurus telling you that MVN/MVP is slow for
<*their* purposes, but these instructions are faster than a loop based move
<algorithm for simple block moves of large areas of memory.  Do you think that
<the Western Design Center engineers had nothing better to do one day than to
<create a totally useless instruction?  They could have left these two opcodes
<open for future expansion.  The 7 cycles is instruction setup time - the move
<occurs at a rate of 1 cycle per byte.

No, it's 7 cycles per byte moved.  I timed an MVN moving one bank (64K) at
452100 +/- 50 ms, which come out to (at 1.023 Mhz on my gs) 7.06 cycles
per instruction.  Considering that there was probably a bit of overhead
at the start or end, and maybe a few interrupts, it looks like 7 to me.


>Brian Willoughby


---
Henry Throop
Internet: throoph@jacobs.cs.orst.edu