u563694848ea@deneb.ucdavis.edu (0040;0000008853;0;250;141;) (04/26/89)
Hi there, I'm currently working on blitter routines, (for that number one amiga application which requires high speed graphics...) and would appreciate some info as to how fast certain operations go. Mainly, what is the difference in speed between doing a full A+B+C->D blit and a simple A->D operation? Does the blit go faster if the dma is turned off (reusing the same data) for one or two channels in a A+B+C->D operation? I don't need absolute speeds, percent offset from the A+B+C->D mode would be perfect. Thanks in advance - Bruce (When am I going to finish that damn game!) Rogers (currently s110018@pollux.ucdavis.edu )
rokicki@polya.Stanford.EDU (Tomas G. Rokicki) (04/26/89)
> Hi there, Howdy, howdy! > Mainly, what is the difference in speed between doing a full A+B+C->D > blit and a simple A->D operation? Does the blit go faster if the > dma is turned off (reusing the same data) for one or two channels > in a A+B+C->D operation? Yep. Simply stated: minimum cycle is 4 clocks (7.16MHz clocks) use of A always costs 2 use of B is always free use of C or D is free use of C and D costs 2 So, we end up with the following table: Channel Clocks/ enabled blitter A B C D cycle ------- ------- N N N N 4 N N N Y 4 N N Y N 4 N N Y Y 6 N Y N N 6 N Y N Y 6 N Y Y N 6 N Y Y Y 8 Y N N N 6 Y N N Y 6 Y N Y N 6 Y N Y Y 8 Y Y N N 6 Y Y N Y 6 Y Y Y N 6 Y Y Y Y 8 Note that you still contend for DMA cycles, so these are maximum speeds. Line mode always runs in 8-clock cycles. -tom
rokicki@polya.Stanford.EDU (Tomas G. Rokicki) (04/26/89)
My mistake; the fifth through eighth lines should read: Channel Clocks/ enabled blitter A B C D cycle ------- ------- N Y N N 4 N Y N Y 4 N Y Y N 4 N Y Y Y 6 I type faster than I think . . . -tom
rokicki@polya.Stanford.EDU (Tomas G. Rokicki) (04/26/89)
> My mistake; the fifth through eighth lines should read:
It gets worse. Completely ignore my previous articles. Here's the
scoop:
Minimum blitter cycle is four clocks (7.18MHz clocks.)
*A* is always free.
*B* always costs 2 cycles.
C or D is always free.
C and D costs two cycles.
Gotta get this right!
-tom