Is byte $2C unstable for cycles?

[Just Jeff]

Good Morning..

 

I don't recall ever running into this before.  Looks like a typical page boundary issue, but no amount of align 256s seem to be able to fix it.

 

The shearing here is my fault, but note how it changes when the taxi is on the line.  So it seems obvious I'm gaining a cycle.

 

I did see this in the debugger.  What's up with the "4-5" cycles  Whatever it is, it appears I'm getting it when the taxi flies through it, but that doesn't make sense either since the branch is taken when the taxi is present.

 

Any ideas?

 

Thanks-

-Jeff

[Thomas Jentzsch]

The "4-5" means, the instruction takes 4-5=-1 cycles when combined with the next instruction, which is skipped with "bit". So 4 in total. Alternatively we could output -1 here, but there might be situations where you want to know the correct number of cycles per instruction. Which is 4 here.

 

To me it looks like (Player0Ptr),y is crossing a page boundary. Then it takes 6 cycles. 

Edited August 21, 2022 by Thomas Jentzsch

[Just Jeff]

Ah so it is the reason then since it a little quicker.  I always thought it was used because it took exactly the same amount of time as the code it skips.  Guess I never looked into it.

 

Thanks!

[Thomas Jentzsch]

In this case the overall code needs the same amount of cycles. As long as (),y doesn't cross a page.

[Just Jeff]

    align 256 

TaxiGearUpGfx:
    .byte %00000000,%00000000,%00100100,%11011010,%11111111,%01000110,%01001000,%00110000	;Taxi, gear up

Player0Gfx: 
    .byte %10000001,%01000010,%00100100,%11011010,%11111111,%01000110,%01001000,%00110000	;Taxi, gear down
Player0_HEIGHT = * - Player0Gfx 

;Additional frames for landing collision checking
    .byte %00000000,%01000010,%00100100,%11011010,%11111111,%01000110,%01001000,%00110000   ;Both legs short
    .byte %00000001,%01000010,%00100100,%11011010,%11111111,%01000110,%01001000,%00110000   ;Left leg short
    .byte %10000000,%01000010,%00100100,%11011010,%11111111,%01000110,%01001000,%00110000   ;right leg short

 

Hmm well I figured this would have prevented that, but it did not.

[Thomas Jentzsch]

Depends on how you setup the pointers and which values Y has.