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AGB - is its memory really this slow?


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#1 Beelzebub   Members   -  Reputation: 122

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Posted 02 January 2002 - 06:16 AM

Trying to write some software render routines and I''m find that work RAM is _really_ slow - some quick tests it appears that memset''ing a 20Kbyte buffer takes a __long__ time. filling 20K using byte pointers takes 8 frames, halfwords 4 frames and 32-bit words still takes 2 frames, surely I''m doing something wrong...? Anybody else had simuliar problems?

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#2 outRider   Members   -  Reputation: 852

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Posted 11 January 2002 - 03:32 PM

I don''t know what you''re doing since I can''t see your code, but yes, using any mode that just hands you the screen buffer is going to be slow since the CPU really isn''t fast enough to do that sort of thing. Use one of the modes that accelerates tiles and sprites.

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#3 outRider   Members   -  Reputation: 852

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Posted 13 January 2002 - 11:39 AM

Or, use the DMA to move stuff around memory. It stalls the CPU, but it''s still faster than using the CPU to do it.

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#4 MirekCz   Members   -  Reputation: 132

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Posted 13 January 2002 - 11:51 AM

outrider:is it possible to use the dma mem transfer with ddraw hi res modes? Currently I''m using MMX stuff to do sysmem->vidmem cpy which takes about 1/90 of a sec on my duron 600 (in 640x480x32bpp mode), the same while doing a sysmem->sysmem copy takes 1/120 of a sec.
Ps. it''s interesting to note, that my bro celeron 400mhz with 66mhz bus takes longer for a sysmem->sysmem copy then a sysmem->vidmem copy (the numbers are 1/52 and 1/57 of a sec if I remember right, for the same mode as my duron, both computers are equipped with an agp2x tnt card)

With best regards,
Mirek Czerwiñski
http://kris.top.pl/~kherin/

#5 MirekCz   Members   -  Reputation: 132

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Posted 13 January 2002 - 11:53 AM

ups... sorry, didn''t notice it''s the console/PDA forum *g*

With best regards,
Mirek Czerwiñski
http://kris.top.pl/~kherin/

#6 outRider   Members   -  Reputation: 852

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Posted 13 January 2002 - 03:24 PM

The speed of the bus really affects sysram->sysram blits, more so than sysram->vram. Anyhow, I have no idea how to get access to the DMA on a PC, I''m too used to getting everything handed to me when PC programming, so this GBA stuff is kind of my learning experience.

#7 s9801758   Members   -  Reputation: 122

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Posted 14 January 2002 - 03:18 AM

Don''t use DMA for clearscreens. Use stmia''s instead.

Cheers,

Jape




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