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Kalms · 11 April 2010, 23:12

Unpacking attribute table with lazy evaluation, 68020+/AGA style:

do it 100% on the CPU side.

Code:

char currentAttributeTable[64] = ...;
char previousAttributeTable[64] = ...;

for (i = 0; i < 64; i++)
{
	if (currentAttributeTable[i] != previousAttributeTable[i])
	{
		write 32x32 pixels x 2 bitplanes to chipmem, with currentAttributeTable[i] as the source info
	}
}

work to be done:
1) 64*2 = 128 bytes of fastmem reads, regardless of number of changes
2) for every byte that has changed, generate pixelmasks to write to chipmem - should take not more than a bunch of cycles
3) for every byte that has changed, write 32*4*2 = 256 bytes to chipmem

If there is a significant numbeer of updates, then 90%+ of the time will be spent waiting for chipwrites to complete. You could actually build a copperlist (or use a blitter interrupt) and get the blitter to perform the memory writes. This would work out because the amount of info that you need to transfer fast->chip is vastly smaller than the amount of chipmem writing that needs to be done.

11 April 2010, 23:12	#8
Kalms Registered User Join Date: Nov 2006 Location: Stockholm, Sweden Posts: 237	Unpacking attribute table with lazy evaluation, 68020+/AGA style: do it 100% on the CPU side. Code: char currentAttributeTable[64] = ...; char previousAttributeTable[64] = ...; for (i = 0; i < 64; i++) { if (currentAttributeTable[i] != previousAttributeTable[i]) { write 32x32 pixels x 2 bitplanes to chipmem, with currentAttributeTable[i] as the source info } } work to be done: 1) 642 = 128 bytes of fastmem reads, regardless of number of changes 2) for every byte that has changed, generate pixelmasks to write to chipmem - should take not more than a bunch of cycles 3) for every byte that has changed, write 324*2 = 256 bytes to chipmem If there is a significant numbeer of updates, then 90%+ of the time will be spent waiting for chipwrites to complete. You could actually build a copperlist (or use a blitter interrupt) and get the blitter to perform the memory writes. This would work out because the amount of info that you need to transfer fast->chip is vastly smaller than the amount of chipmem writing that needs to be done.