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Old 15 July 2017, 20:35   #1
sandruzzo
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Blitter vs Cpu on Aga

I know that Aga Blitter is the same as ECS, but due to more memory bandwidth
Blitter can go full speed.

What CPU is Blitter worth? 020, 030?
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Old 16 July 2017, 01:29   #2
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According to the GameSmith documentation, for making bobs it is equivalent to an 040.
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Old 16 July 2017, 01:45   #3
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030 will be faster than blitter in most things, especially if real fast memory is available as well.
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Old 16 July 2017, 09:08   #4
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Originally Posted by Galahad/FLT View Post
030 will be faster than blitter in most things, especially if real fast memory is available as well.
030 50mhz or even 28 mhz?
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Old 17 July 2017, 00:17   #5
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Originally Posted by sandruzzo View Post
030 50mhz or even 28 mhz?
Assuming the 030 accesses RAM using the same number of clock cycles as the 68k (which is false, it uses less), at 28MHz it will have a RAM bandwidth around four times higher than the 68k (28 = 7 * 4, 7mHz = original clock frequency).

If you run a mem copy in a tight loop which fits into the cache, this means that it is not slowed down too much by instruction fetches and will almost have this full bandwidth available for data reads and writes. This is grossly the same speed as the blitter with its four (3 read, 1 write) channels.
(If you write to chip RAM you would have to take into account that that its bandwidth is limited in addition to being used by the chips as the Galahad kitten hinted.)

Sure, this is just a back of the envelope approximation but this gives a reasonable idea of what to expect.

Hope this helps.
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Old 17 July 2017, 08:29   #6
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@ReadOnlyCat

I'm not talking about Memory acces only, but real operation like direct copy D = A, and cookie cut blit operation, Assuming that blitter and cpu can run at full memory speed
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Old 17 July 2017, 10:17   #7
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Quote:
Originally Posted by sandruzzo View Post
@ReadOnlyCat

I'm not talking about Memory acces only, but real operation like direct copy D = A, and cookie cut blit operation, Assuming that blitter and cpu can run at full memory speed
In a direct copy the 020 is the same speed if Fast RAM is available. Cookie cutting is more like an 040 unless you can avoid shifting bits.
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Old 17 July 2017, 10:18   #8
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I'm not talking about Memory acces only, but real operation like direct copy D = A, and cookie cut blit operation, Assuming that blitter and cpu can run at full memory speed
Depends on the operation... The blitter can shift bits left/right faster than an 030 I think.

However, if you are reading graphic data from fast memory and only writing to chip, the 030 can be faster because fast RAM has more bandwidth than chip.

The ideal scenario would be to use both the blitter and CPU, with the CPU reading from fast memory and only doing the final write into chip.
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Old 31 July 2017, 16:14   #9
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"Normal" code: (max-optimized general-purpose function) Linedraw and cookie-cut should still beat the 020/030. All other operations, or small blits, say 32 words or less, use the CPU.

In special cases there will always be some tricks to pull to at least give the visual impression that the CPU has beaten the Blitter.

In all cases it will be up to screen size+depth and intelligent fighting with the DMA for the coveted slow chip RAM.
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Old 31 July 2017, 19:44   #10
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"Normal" code: (max-optimized general-purpose function) Linedraw and cookie-cut should still beat the 020/030. All other operations, or small blits, say 32 words or less, use the CPU.

In special cases there will always be some tricks to pull to at least give the visual impression that the CPU has beaten the Blitter.

In all cases it will be up to screen size+depth and intelligent fighting with the DMA for the coveted slow chip RAM.
So blitter wasn't so bad. If we had 32bit 14mhz on aga....
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Old 31 July 2017, 21:11   #11
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So blitter wasn't so bad. If we had 32bit 14mhz on aga....
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Old 06 August 2017, 20:47   #12
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Quote:
Originally Posted by sandruzzo View Post
So blitter wasn't so bad. If we had 32bit 14mhz on aga....
Actually, 16 bits at 14 MHz would saturate the fast page access if buffered properly. Some parts of the AGA Alice were clocked at 28 MHz so the blitter could have been miniaturized to 8 bits for a smaller die and a single chip solution at that clock speed.
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Old 07 August 2017, 09:18   #13
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Actually, 16 bits at 14 MHz would saturate the fast page access if buffered properly. Some parts of the AGA Alice were clocked at 28 MHz so the blitter could have been miniaturized to 8 bits for a smaller die and a single chip solution at that clock speed.
Yes mate! Blitter with few changes would had ben so powerfull!
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