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Old 20 August 2015, 22:06   #240
Join Date: Jan 2010
Location: Kansas
Posts: 1,284
Originally Posted by Adrian Browne View Post
So trouble brewing in Apollo core world eh?
Trouble? No, there is no new trouble. Gunnar likes to be the leader of obedient followers. Unfortunately, he tends to overwhelm other leaders and loses the advantages of a diverse group. This makes his job more difficult but perhaps he may succeed doing everything his way. I believe his technical processor design knowledge is sound.

Originally Posted by meynaf View Post
So once MOVEM.L is done, doing MOVEM.W is peanuts ? (As the special format is what's tough here, when you have it, you can reuse it, right ?)
MOVEM.W is not much more difficult although register destinations require more resources to do the sign extensions. Again, it would be nice to give the resources to MOVEM.W a word pair in cache to/from registers in 1 cycle. Some other DSP like processors or processors with DSP like extensions have special instructions to load and store pairs but it would be better if we could speed up what we have rather than introduce new instructions. Loading separately with MOVE requires instruction scheduling to avoid the 1 read or write per cycle limitation and is not always possible. Adding some SIMD like instructions like ADD2W.L and ADD4B.L would be simple and could help also but it would be good to see what a separate SIMD design could do first. I know you well enough that you would probably say forget the SIMD and add MOVEM.B though .

Originally Posted by meynaf View Post
MOVEM needs to be reasonably fast, while MOVEP does not. Isn't it easier when it can be slow ?
Basically it's just a bunch of shift + move.b, and these already exist in the cpu. It's not like if we want it to run in 1 clock.
Any instruction which takes more than 1 cycle adds complexity to the pipeline design and is more costly. The 68k does and probably always will support multi-cycle instructions so some of the support for multi-cycle instructions is already in place. The actual cost likely depends on the specific 68k design.
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