ST bus cycles

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2 total messages Started by Landon Dyer Mon, 03 Feb 1986 20:26

#2372

Author: Landon Dyer
Date: Mon, 03 Feb 1986 20:26

20 lines
1410 bytes

I sent a bogus description of the ST's bus cycle architechure to
this list.  I apologize.  This morning I collared one of the hardware
people here and shook the real description out of him:

There are two 250ns windows.  One window is for "static" system requests
(video DMA and memory refresh).  The other window is available for disk
DMA, blitter DMA, and processor accesses.  Refresh cycles are done during
horizontal and vertical blank (and take, say, 5% of the first window).
When the first window is not being used, it is available to fill requests
that would otherwise go to the second window.

I don't know exactly how much bandwidth is used by memory refresh cycles,
but it is low.  5% is probably not too far off.

Please forget my earlier misdescription of the bus architecure ....


-landon
-------

Re: ST bus cycles...BLITTER?!?!?!?!?!?!?

#2379

Author: Jan Gray
Date: Wed, 05 Feb 1986 15:45

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In article <12180482042.28.G.DYER@SU-SCORE.ARPA> G.DYER@SU-SCORE.ARPA (Landon Dyer) writes:
>
>There are two 250ns windows.  One window is for "static" system requests
>(video DMA and memory refresh).  The other window is available for disk
>DMA, blitter DMA, and processor accesses.  Refresh cycles are done during
      ^^^^^^^^^^^
>horizontal and vertical blank (and take, say, 5% of the first window).
>When the first window is not being used, it is available to fill requests
>that would otherwise go to the second window.

WHAT BLITTER?????  Somewhere in the documentation I saw an interrupt
vector for "gpu blt done"...but nothing else!  I can't believe there
is special hardware for bitblt on the ST, since vro_cpyfm() is
too damn slow(*).  Unless, of course, the "blitter" is only useful for
doing no-skew, whole word transfers...

Please please please tell us more.  Maybe you could even fill us in on
how to do bitblt from the line A vector (since my documentation (and
others) were missing the last n pages of the "Long Awaited Line A
Document").

Thanks,
Jan Gray	Looking Glass Software, Waterloo Ont.	(519) 884-7473

p.s. Are you *the* l. dyer who wrote the BIOS, etc (or at least had his
name on the listings?)

(*) That is, for doing large image processing tasks like "spreading" the
screen, running life on the whole screen etc.  (BTW, can anyone beat
400,000 life cell-generations per second on their ST?)

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