10 May 2024, 03:23 | #1 |
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AGA DMA slots
I posted in another thread that the maximum chipram access read/write on AGA 32bit processors is around 7 megabyte per second. That would be 140Kilobyte per second and an 8 bitplane screen is ~80 kilobyte in size.
That throughput should be more than enough for full screen updates on a 256 colour 8 bitplane screen. However, I realise the dma slots are split between bitplane, blitter, sprites, copper, audio and floppy access. What is the DMA slot breakdown between these and using an 8 bitplane 256 colour screen? Note: I realise the blitter is dynamic in terms of loading it/arming it for transfer but outside of that what are the DMA slots for the other tasks? Does scrolling the screen use DMA and are what cost to DMA? |
10 May 2024, 04:55 | #2 |
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As far as I understand it, the old hardware reference manual DMA cycle page will generally still apply, just with the sprite and display cycles being able to move 32 or 64 bits per cycle instead of just 16: http://amigadev.elowar.com/read/ADCD.../node012B.html
Horizontal scrolling needs an extra word of data at the beginning of the display area, vertical scrolling has no DMA overhead. Copper and blitter remain 16 bit so they're not any faster, but may have more free cycles available to use if using the 32 or 64 bit modes to reduce the number of display DMA cycles. |
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