Score board bug

[42bs]

What I did first was

loop:
  prepare line 
  wait for blitter
  start blitter
  goto loop

Then I did remove the 'wait for blitter' and saw no glitches. Means the blitter reads the line quicker than the GPU can write to it.

_But_ while doing this the 68k was doing a lot of stuff.

Stopping it helped a lot to speed up GPU only code. Next is using the blitter again.

 

 

Edited April 27, 2022 by 42bs

[Zerosquare]

I'm not sure if this is what you're talking about, but the Blitter has a higher bus priority than the 68K. Which means that from the 68K's point of view, the blitter is never busy -- when it actually is, the 68K is paused and can't execute code, so it doesn't see it.

Edited April 27, 2022 by Zerosquare

[JagMod]

1 hour ago, 42bs said:

What I did first was

loop:
  prepare line 
  wait for blitter
  start blitter
  goto loop

 

 

 

This has the potential danger of the GPU overwriting parts of the line before the Blitter has finished reading it.

If you see no glitches, its most likely the GPU is spending enough time doing something besides writing to the line buffer, and the blitter stays ahead of the GPU.

It's still a race.

[42bs]

7 hours ago, JagMod said:

This has the potential danger of the GPU overwriting parts of the line before the Blitter has finished reading it.

If you see no glitches, its most likely the GPU is spending enough time doing something besides writing to the line buffer, and the blitter stays ahead of the GPU.

It's still a race.

Sure, in a non-size limited program I would not remove the test.

[42bs]

Added double buffering and it works w/o glitches and w/o waiting for the blitter.

The "gain" is not mind boggling, but at least a few dozen scan lines. Not enough to draw 320x240x16 pixel image in one frame, though.

[Cyprian]

2 minutes ago, 42bs said:

Not enough to draw 320x240x16 pixel image in one frame, though.

well, let's do some math:

320 x 240 means 76 800 pixels. This is 3 840 000 pixels per second in case of 50 FPS.

Therefore when we have 30 cycles per pixel, the GPU should be clocked with 115MHz

[+CyranoJ]

3 minutes ago, Cyprian said:

Therefore when we have 30 cycles per pixel, the GPU should be clocked with 115MHz

 movei #115,r0
 movei #GPU_CLK_SPD,r1
 store r0,(r1)

Simplez!

[42bs]

41 minutes ago, CyranoJ said:

 movei #115,r0
 movei #GPU_CLK_SPD,r1
 store r0,(r1)

Simplez!

Boy, such a simple solution. And I waste hours looking to speed up ?

 

[Cyprian]

@CyranoJ awesome

[42bs]

50 minutes ago, Cyprian said:

well, let's do some math:

320 x 240 means 76 800 pixels. This is 3 840 000 pixels per second in case of 50 FPS.

Luckily the Blitter can at least write 64bit at once.

 

[Cyprian]

Just now, 42bs said:

Luckily the Blitter can at least write 64bit at once.

 

yep,

 

would be cool to have MMX instructions and calculate 4 pixels at once.