DLI jump instructions

[MaPa]

Hi, I'm just curious as I don't have real ATARI. Is the address after JVB (jump and wait for vertical blank interrupt) really needed or it just waits for VBI and after it it just starts DLI from address you defined in DLIST registers ($D402,3 or shadow regs $230,231) ? In emulator I didn't noticed any difference if I put after JVB instruction LSB and MSB of DLIST starting address or random data, zeros etc. it works just fine.

Edited February 14, 2008 by MaPa

[Heaven/TQA]

maybe you haven't seen a difference because the system vbl is restoring the dlist vector...

[NRV]

hmmm.. good question

 

I believe that I had used chained display lists in some project many years ago

(JVB of DL1 points to DL2, and JVB of DL2 points to DL1..) and it worked, but I

don't know what happens in the emulator

 

anyway, if you have the OS VBI active, maybe the process that copies the shadow

register ($230,1) to the rom register ($D402,3) resets the address used in the JVB??

 

NRV

[Rybags]

The OS does it for you, but there's no guarantee it'll do it every time since it's in VBlank Stage 2.

 

Just put random data in the address, then press some keys - about 1 in 10 or so, you'll get garbage or a blank screen flashing.

[Sheddy]

I believe that I had used chained display lists in some project many years ago

(JVB of DL1 points to DL2, and JVB of DL2 points to DL1..) and it worked, but I

don't know what happens in the emulator

 

I can confirm chained display lists work correctly in Atari800WinPlus 4 at least