6502 assembly language routines

[deanb01]

I've started porting my Z80 library routines (originally written for the ZX Spectrum) to 6502 for the Beeb/Electron. So far ported fast plot, line and circle (Mode 2), a simple sprite handler and a handful of other routines.

The sprite routine in particular, is heavily influenced by one published by Kevin Edwards in The Micro User (1985).

These are available on GitHub, warts and all, under an MIT license, are currently a work-in-progress, and will be updated on a semi-regular basis.

https://github.com/breakintoprogram/lib-acorn-bbc

I'm doing this to brush up on my 6502, and learn more about programming the Beeb, and sharing in case they may be of use to others.

[BigEd]

Nice one - thanks for sharing, and using an open source license.

[tricky]

Looks good.
I would have to reverse the loops to remove the compares
Have you read the threads on fast line drawing and the EOR filling routine?

[0xC0DE]

Thanks for contributing these to the community, Dean!

[deanb01]

Looks good.
I would have to reverse the loops to remove the compares
Have you read the threads on fast line drawing and the EOR filling routine?

Thank you!
I think for the line/circle routine I'd probably do what I did on the Spectrum version, calculate the screen address once, then as the pixel moves, just increment/decrement address and plot pixel(s) accordingly. Should save a considerable number of cycles from the loop, though will make the circle routine fun - tracking 4 lots of screen row addresses and 8 pixel positions!
My 6502 is sub-optimal at the moment - it's been 20-odd years since I last coded it (on the NES), and I'm much more proficient in Z80, so happy to pick up any tips from the pros. And I know very little about the Beeb hardware!

[deanb01]

Nice one - thanks for sharing, and using an open source license.

Thank you!

[deanb01]

Thanks for contributing these to the community, Dean!

No worries - as long as folk are happy to put up with my pidgin 6502! Glad the Acorn community is alive and well. Partly got you to blame for getting me hooked with my Electron by the way!!

[0xC0DE]

Thanks for contributing these to the community, Dean!

No worries - as long as folk are happy to put up with my pidgin 6502! Glad the Acorn community is alive and well. Partly got you to blame for getting me hooked with my Electron by the way!!

You're welcome!

[alastairhm]

Looks like a good resource, I'm sure I'll make use of it on my trip back into 6502.

Is there a "best practice" way to include these libraries in your own code?

With beebasm, I've been playing about with INCLUDE keyword.

Code: Select all

 \ Example 3.2

 INCLUDE "../../lib/constants.asm"
 screen = &7E40
 mode   = 6

 ORG &2000

 .start
     LDA mode
     JSR screenmode
     LDX #0
     LDY #0
     JSR tab
     LDA #15
     JSR printhex
     LDX #0
     LDY #1
     JSR tab
     LDA #&32
     JSR printhex
 .finish
     RTS
 .screenmode
     INCLUDE "../../lib/screenmode.asm"
 .printhex
     INCLUDE "../../lib/printhex.asm"
 .tab
     INCLUDE "../../lib/tab.asm"
 .end

 SAVE "MyCode", start, end