Dual Playfield Scroll Demo

[DaveInFL]

I am sure the answer to this is quite easy, but as I am new to programming in asm and trying to understand everything most of it, if not all of it, is above me

I am using FS-UAE on a Mac and I have installed Classic WB 3.1. I have the A4000 configuration set with 2MB chip ram, 64MB Zorro III Fast Memory using the 68040 CPU. I find this WB environment nice and responsive and easy to use ASMOne to enter the demo programs in Amiga Systems Programmers Guide. Most of what I have been running has been fine, except the dual playfield scroll demo. I suspect it's simply because the A4000 configuration is just too powerful/fast and as such the scroll demo looks super jerky, or it is simply scrolling so fast it appears jerky. When I boot up FS-UAE with the A500 config the demo runs perfect.

So, is there anyway I can get this to run with the A4000 configuration as it does on the A500, or is that simply just not possible?

I have attached the script for reference.

Sorry if this is something of a stupid question. I even tried running it under my A1200 configuration and that was ugly too.

[phx]

The main loop waits for VPOS=16 and has not very much to do. I could imagine that a faster system might finish the work on the same raster line and, as a consequence, executes again immediately?

[DaveInFL]

Yes, that could be it. I'll take a look and see what I can do....break it probably...LOL

[DanScott]

As a quick fix, try waiting for line 16, then again for line 17 before proceeding

[DaveInFL]

Originally Posted by DanScott

As a quick fix, try waiting for line 16, then again for line 17 before proceeding

Thanks, that did the trick. However, the horizontal scrolling is not working correctly on the left hand side, the new block just suddenly appears instead of smooth scrolling onto the screen, like the horizontal screen is pushed over to the right so the new block is not appearing in the hidden part of the screen. When using the A500 configuration the horizontal scrolling is perfect, just smoothly comes in from the left hand side.

[DanScott]

Perhaps on the A4000 config, your code is running with data fetch mode (FMODE register) already set to 32bit or 64bit bitplane fetch ?

Maybe try clearing FMODE register where you also set up your DIWSTART etc..


FMODE = $1FC

move.w #$0000,FMODE(a5)

[DaveInFL]

Originally Posted by DanScott

Perhaps on the A4000 config, your code is running with data fetch mode (FMODE register) already set to 32bit or 64bit bitplane fetch ?

Maybe try clearing FMODE register where you also set up your DIWSTART etc..


FMODE = $1FC

move.w #$0000,FMODE(a5)

Dan, no idea what fetch mode is but I will give it a try and see what happens. Thanks for the suggestion.

[DaveInFL]

Originally Posted by DaveInFL

Dan, no idea what fetch mode is but I will give it a try and see what happens. Thanks for the suggestion.

Yup, that worked perfectly. Any chance you could explain just exactly what that did for me please?

[DanScott]

FMODE (fetch mode register) controls how much data is read by the DMA for bitplanes (and for sprites), and is an AGA only register.

When fetchmode for bitplanes is x2 or x4 (only available on AGA), it also affects DDFSTART/DDFSTOP and modulos. Also, the alignment in memory for x2 and x4 changes too.

[DaveInFL]

Originally Posted by DanScott

FMODE (fetch mode register) controls how much data is read by the DMA for bitplanes (and for sprites), and is an AGA only register.

When fetchmode for bitplanes is x2 or x4 (only available on AGA), it also affects DDFSTART/DDFSTOP and modulos. Also, the alignment in memory for x2 and x4 changes too.

Thanks for that explanation Dan.