Copper question

[leonard]

Hi,
I'm used to do ATARI demos, and did some AMIGA stuff too. but I never really played with the COPPER till now. I did a simple test to fill the screen with 8 pixels width columns. The goal is to not wait for a specific Y each raster line. My test is working BUT somewhere in the screen the WAIT instruction seems to not work anymore. Screenshot is better than my explain. I know there is some care to take at raster line 255, but the issue is far before the 255 line.
Any idea?



code producing the copper list:

copperBuild:
			move.l	pCopperList(pc),a1
			move.l	#$3001fffe,(a1)+	; first wait for line $30, pos x=0			
			move.w	#$0031,d2			; each line, wait opcode: don't care about Y line ($00) and wait for X pos $31
			move.w	#200-1,d0			; 200 lines high

.loopY:		move.l	#$01800ff0,(a1)+	; set screen to yellow just before executing the WAIT
			move.w	d2,(a1)+			; wait opcode
			move.w	#$00fe,(a1)+		; don't care about Y value			
			moveq	#42/2-1,d1			
			move.l	#$01800f00,(a1)+	; RED marker to see when the WAIT finished

.loop:		move.l	#$01800fff,(a1)+	; put some "white & black" 8 pixels columns
			move.l	#$01800000,(a1)+
			dbf		d1,.loop
			
			dbf		d0,.loopY
			move.l	#-2,(a1)+
			rts

PS: I did my test in latest WinUAE, using OCS chipset.

[Toni Wilen]

Only bits 0 to 6 of vertical position can be masked. Mask bit 7 is blitter finished disable bit.

This is very common "issue".

[leonard]

ok. I did a fix using:

move.w #$80fe,(a1)+ ; don't care about Y value


but it produces exactly the same image.

Do you mean I have to do specific code at the raster line 127, as I should do for raster 255?

[Leffmann]

The key to working out all these vpos and hpos issues is realizing that you have to break down the display in segments of 256 lines, not just consider specifically line 255, since the Copper only sees the 8 least significant bits of vpos, and because bit 7 of the vpos mask is always set, you can't completely ignore vpos for the kind of effect you're doing here, you have to at least know whether you're in the upper or lower half of the current segment.

So in your case, just setting bit 15 in register D2 once you reach line 128 will fix the problem.

[leonard]

Originally Posted by Leffmann

So in your case, just setting bit 15 in register D2 once you reach line 128 will fix the problem.

oh I get it! It works! thanks a lot guys

[leonard]

last question: I read somewhere that CPU shares the same memory slot than COPPER. In case of OCS machine with only SLOW ram extension, does it mean if I'm using COPPER MOVE all around the screen, CPU is blocked? (no CPU free at all?)

[Toni Wilen]

Originally Posted by leonard

last question: I read somewhere that CPU shares the same memory slot than COPPER. In case of OCS machine with only SLOW ram extension, does it mean if I'm using COPPER MOVE all around the screen, CPU is blocked? (no CPU free at all?)

CPU can use any available cycle (Documentation talking about CPU only using even cycles is wrong): CPU is not blocked if Copper is doing MOVEs. (and no other DMA channel is stealing other cycles)

[Kalms]

http://eab.abime.net/showthread.php?t=72575 contains more in-depth discussion of chipbus activity and prioritization.