Programming NES games in C article

[Nioreh]

Thanks Shiru, but I think this version introduced another bug. Now I have to hold the A-button to get any other button to register.

Bug appears on nestopia and real hardware. Not in FCEUX.

[Shiru]

Fixed, temporary files are updated.

[Nioreh]

Wow, that was fast. Thanks!

[albailey]

Shiru, do you have the source code anywhere for the runtime.lib code?

Namely, I am interested in seeing what popa and popax do.

I noticed when looking at the code for some of the neslib.s (I was looking at oam_spr) routines that there are lots of calls to "jsr popa" because that call takes 4 arguments.

Typically jsr can be a bit heavy (6 cycles for JSR plus another 6 for its RTS) and I wanted to see if any of the routines could be optimized.

Al

[Shiru]

It is in the CC65 sources, you can download them, there are many functions. I quote these two here:

Code: Select all

;
; Ullrich von Bassewitz, 25.10.2000
;
; CC65 runtime: Pop a from stack
;

       	.export	  	popa
	.importzp	sp

        .macpack        cpu

.proc	popa

.if (.cpu .bitand ::CPU_ISET_65SC02)
	lda	(sp)
.else
	ldy 	#0              ; (2)
 	lda	(sp),y		; (7) Read byte
.endif
      	inc	sp              ; (12)
       	beq	@L1             ; (14)
	rts                     ; (20)

@L1:	inc	sp+1
	rts

.endproc

Code: Select all

;
; Ullrich von Bassewitz, 25.10.2000
;
; CC65 runtime: Increment the stackpointer by 2. For performance reasons,
; 		this modules does also contain the popax function.

       	.export		popax, incsp2
	.importzp	sp

        .macpack        cpu

; Pop a/x from stack. This function will run directly into incsp2

.proc	popax

	ldy  	#1
   	lda	(sp),y	   	; get hi byte
       	tax	     	   	; into x
.if (.cpu .bitand ::CPU_ISET_65SC02)
	lda	(sp)		; get lo byte
.else
   	dey
   	lda	(sp),y		; get lo byte
.endif

.endproc



.proc	incsp2

        inc     sp              ; 5
        beq     @L1             ; 2
        inc     sp              ; 5
        beq     @L2             ; 2
        rts

@L1:    inc     sp              ; 5
@L2:    inc     sp+1            ; 5
        rts

.endproc

[Makdaam]

Thanks for the great article, however I've got some problems with linking:

Code: Select all

$ ld65 --version
ld65 V2.13.9 - (C) Copyright 1998-2009, Ullrich von Bassewitz

$ ld65 -o main.nes crt0.o example1.o runtime.lib -C nes.cfg 
ld65: Error: Wrong data version in `runtime.lib

If I'm linking without runtime.lib I get:
"ld65: Error: nes.cfg(82): Attribute expected"
82 is the line with "__STACKSIZE__ = $0500; # 5 pages stack"

I've never developed on the NES platform (or used the cc65 binutils) before, also I'm trying to build the examples on Ubuntu.

[Shiru]

I have ld65 2.13.2. Perharps you have some newer or WIP version of CC65? Where to get Windows build of this version?

Also, order of ld65 parameters could be important.

[tepples]

Version 2.13.3 is uploaded to the FTP site. Here's the changelog summary from 2.13.2 to 2.13.3 from the 2.13.3 release announcement.

cc65:

• Fixed some macro issues.
• Static const local data goes into RODATA, not DATA.
• Fix problem when converting function to void pointer.
• Fix register info for several runtime functions. Result was invalid code.
• Fix an error in the runtime division routine.
• Fix internal error caused by error recovery (or lack of).
• Fix invalid handling of signed int types in some cases.
• Fix and improve the code for compares.
• Disallow __asm__ on global level.
• Fix problem with access to structs returned by functions.
• Fix an internal error in the code generator.

ca65:

• Fix error handling in .LEFT.
• Fix problem with .REPEAT.
• Fix problem with alignments >= 256 bytes.
• Fix some macro issues.

libraries:

• Fixed problems with 80 column mode (C128 library).
• Remove final jump to RESTOR for all CBM platforms (cc65 libraries).
• Merge back Olivers C interrupt handling code (cc65 libraries).
• The LINE function mistakenly enabled the BASIC ROM (TGI driver for C64).
• Fix some issues with conio scrolling (C128 library).
• Add missing export for CBM510 platform (cbm510 library).
• Merge back POSIX directory routines for the Atari (atari library).

da65:

• Fix smbx and rmbx instructions.

general:

• Fixed/improved several error messages (all tools).
• Several documentation changes.
• Several documentation fixes and improvements.

[Shiru]

2.13.3 also works for me, no changes were needed.

[Makdaam]

I got it from a repo at http://www.trikaliotis.net/debian... but I guess building it from source would be a better idea.

[rainwarrior]

Shiru, I was wondering what you ended up putting in your runtime.lib.

Is it just runtime/ plus common/zerobss.s ?

[Shiru]

It is standart cc65 runtime, recomplied by me. Nothing is added there, as far as I remember - none of my code for sure. I don't really remember why I did recompile it. I think I used nes.lib initially that did contain the runtime, but a ton of unneeded stuff as well, so I replaced it with the runtime only, that does not have anything platform-specific (600 to 100K in size).

[rainwarrior]

I've been looking over it, compiling my own version. I had been using yours, but I wanted to get a better idea of what's in there.

There is basically nothing useful in the nes/ lib source, unless you want to make a text only program maybe, and I think it's a good idea to replace crt0. Luckily all the runtime/ stuff is modularized, so stuff you don't used is not linked in anyway.

Apparently there's a few things I need from common/ so far zerobss.s and copydata.s were needed. Probably I will need to add more as I go along and I get link errors, but I think most of common/ I want to leave out. I'm keeping a list as I go. I'll release source and information once I've finished my current project, so anyone who's interested might learn from it.

[Shiru]

Here are the runtime sources that I used to compile the runtime.lib.

[rainwarrior]

Ah, that looks exactly like runtime/ + common/zerobss.s like I suspected. That answers my earlier question.