Blitter Speed

sandruzzo · 09 September 2022, 06:00

I did a simple to test blitters' speed with a channel enabled and disabled with cookie-cut operation. It seems that there is no difference at all! I've used 4 planes interleaved bitmap 320x256. My blitting is 48*124 pixel.

There is no visible difference at all. White coppers' line is full coockie-cut with ABCD enabled. Red one is full coockie-cut but only BCD enabled.

It seems that A channel is well pipelined. Quite interesting

[IMG]

[/IMG]

a/b · 09 September 2022, 07:32

That's because it has idle cycles (enabled A = fetch, disabled A = idle), so it takes the same period of time but fewer memory accesses.

roondar · 09 September 2022, 11:45

You should be able to get the result you're looking for by using a Blitter channel combination of ACD instead of BCD, which does use all the cycles (barring one at the start and one at the end).

Just a matter of switching what's in channel A & B (I presume you have a pre-loaded value in A at the moment so that would be put in B instead) and rewrite the minterm to match the new channel combo

Edit: hmm, I did forget about the first/last word mask there for a bit. That may be an issue with some types of blit, though not normally for a 'standard' cookie-cut blit.

sandruzzo · 09 September 2022, 13:11

@roondar

I just wanted to inquire if it could be worth aid blitter with cpu during cookie-cut operation. Since it seems that A channel is for free, I won't do more tests

a/b · 09 September 2022, 14:26

During regular blits (e.g. cookie cut) A is not for free, it's the opposite. A is hardcoded, it always takes a slot, and if you disable it then the blitter waits/idles instead of reading from memory.

Related to what Roondar said, if your blit has size=3 words, using ABCD that's:
**** **** **** (duration=12, 12 r/w + 0 idle)
Using BCD:
-*** -*** -*** (duration=12, 9 r/w + 3 idle)
While using ABD or ACD:
*** *** *** (duration=9, 9 r/w + 0 idle)
So if you are e.g. blitting with a static 16-bit mask in bltXdat, it's better to put it in B or C, and not in A. Well, unless you specifically want idle cycles and prolonged blits so that the cpu has more freedom.

sandruzzo · 09 September 2022, 21:43

Indeed its faster with ACD, but I want see if I can load mask with cpu and keep that speed

[IMG]

[/IMG]

09 September 2022, 06:00	#1
sandruzzo Registered User Join Date: Feb 2011 Location: Italy/Rome Posts: 2,291	Blitter Speed I did a simple to test blitters' speed with a channel enabled and disabled with cookie-cut operation. It seems that there is no difference at all! I've used 4 planes interleaved bitmap 320x256. My blitting is 48*124 pixel. There is no visible difference at all. White coppers' line is full coockie-cut with ABCD enabled. Red one is full coockie-cut but only BCD enabled. It seems that A channel is well pipelined. Quite interesting [IMG][/IMG]

09 September 2022, 11:45	#3
roondar Registered User Join Date: Jul 2015 Location: The Netherlands Posts: 3,411	You should be able to get the result you're looking for by using a Blitter channel combination of ACD instead of BCD, which does use all the cycles (barring one at the start and one at the end). Just a matter of switching what's in channel A & B (I presume you have a pre-loaded value in A at the moment so that would be put in B instead) and rewrite the minterm to match the new channel combo Edit: hmm, I did forget about the first/last word mask there for a bit. That may be an issue with some types of blit, though not normally for a 'standard' cookie-cut blit. Last edited by roondar; 09 September 2022 at 12:00.

09 September 2022, 21:43	#6
sandruzzo Registered User Join Date: Feb 2011 Location: Italy/Rome Posts: 2,291	Indeed its faster with ACD, but I want see if I can load mask with cpu and keep that speed [IMG][/IMG]

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09 September 2022, 07:32	#2
a/b Registered User Join Date: Jun 2016 Location: europe Posts: 1,039	That's because it has idle cycles (enabled A = fetch, disabled A = idle), so it takes the same period of time but fewer memory accesses.

09 September 2022, 13:11	#4
sandruzzo Registered User Join Date: Feb 2011 Location: Italy/Rome Posts: 2,291	@roondar I just wanted to inquire if it could be worth aid blitter with cpu during cookie-cut operation. Since it seems that A channel is for free, I won't do more tests

09 September 2022, 14:26	#5
a/b Registered User Join Date: Jun 2016 Location: europe Posts: 1,039	During regular blits (e.g. cookie cut) A is not for free, it's the opposite. A is hardcoded, it always takes a slot, and if you disable it then the blitter waits/idles instead of reading from memory. Related to what Roondar said, if your blit has size=3 words, using ABCD that's: ** (duration=12, 12 r/w + 0 idle) Using BCD: -* -* -* (duration=12, 9 r/w + 3 idle) While using ABD or ACD: * * *** (duration=9, 9 r/w + 0 idle) So if you are e.g. blitting with a static 16-bit mask in bltXdat, it's better to put it in B or C, and not in A. Well, unless you specifically want idle cycles and prolonged blits so that the cpu has more freedom.

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