Port to ASM6

[pinobatch]

Pently is made for ca65. But loopy wrote in the README file for his ASM6 assembler that ca65 "took too much work to set up", and several users of NESdev BBS agree.

In a forum post about MML processors, Pokun considers a requirement of ca65 to be a disadvantage for NSDL. In a forum post about music engines used by a ROM hacker turned original game programmer, dougeff expressed a bit of frustration about upstream (us) being ahead of his port to ASM6.

So consider ways to accommodate ASM6 users without having to Write Everything Twice (WET). This may involve a preprocessor of some sort to turn ca65 assembly source code to something ASM6 accepts. (I wrote a similar preprocessor for NESASM years ago as part of Action 53.) Steps I know I'll need to take:

• Assembler directives need not have a leading dot.
• equ replaces =; = instead replaces .set
• db or byte replaces .byt
• dw or word replaces .addr
• dsb replaces .res
• rept (with no second argument) replaces .repeat; emulate the second argument with =.
• rept 1 replaces .scope
• No .bss; emulate it with .enum and = $. May need host to allocate both zero page and BSS memory.
• No other .segment; treat code and read-only data the same.
• No .proc; emulate it by either prefixing the namespace to non-@ labels or perhaps wrapping the body in a .rept 1.
• No .assert; emulate it with if.
• No second argument to .assert either, but it can be emulated with if.
• Unnamed labels follow the x816 convention (-, --, +foo), not the ca65 convention (:). Change them to @-labels in the source code.

[Qix-]

I like ASM6 already. Do we know the percentage of users currently using ASM6 vs. CA65?

[darkhog]

Actually, dots before directives like byte in ASM6 are optional, but legal. So you don't have to remove them. I'm using them for consistency & readability anyway. This would simplify the converter.

[pinobatch]

100 percent of NESmaker users are using ASM6

[pinobatch]

I may not want to bother making the tool translate the scope resolution operator, which allows referring to labels inside a different .proc. If we use rept 1 to replace .scope, we can't do this. Fortunately, most of the over 80 uses of scope resolution are .if :: to force use of the top-level scope as a workaround for cc65 issue #796 in order to prove to ca65 that a constant isn't redefined later in the same scope. For the others, break out a separate .proc with a fallthrough.

• pently_resume_music::have_music_playing becomes pently_set_music_playing
• skip_to_row_top::bottom becomes pently_skip_to_row
• pently_play_note::skipAttackPart becomes pently_play_note_rts
• sustain_phase::silenced becomes silence_out_volume

Anonymous labels should be easier to translate automatically.

• At the start of translation, set a counter to 0.
• When a line's label is :, increase the counter by 1 and then emit a label of the form @ca65toasm6_anonlabel_1:.
• Replace :+ in an expression with the next @ca65toasm6_anonlabel_{n+1}.
• Replace :- in an expression with the next @ca65toasm6_anonlabel_{n}.

[pinobatch]

As of March 2019, Pokun still rejects NSDL because of ca65.

[pinobatch]

And right now I'm stuck on what to use to replace .ifblank and .ifnblank in a couple macros in pentlyseq.inc

[pinobatch]

Right now I'm stuck on trying to get pentlyseq.inc macros like sfxdef to work in ASM6. Here's an MCVE for what I'm seeing, heavily reduced from the definition of sfxdef. It gives an Illegal instruction error in ASM6, but no error if I remove the include guard or remove the use of addy within the macro.

; include guard mcve
; changing dw addy to dw 0 causes no error
; removing the ifndef/endif causes no error
ifndef INCLUDE_GUARD
INCLUDE_GUARD = 1
macro hello addy
dw addy
endm
endif
base $C000
hi:
hello data1
hello data2
data1:
data2:

[pinobatch]

Good news: 63ff9ae got all 10 sample songs playing. The next steps I can see:

• [ ] Preprocess the code and data separately, possibly involving changes to pentlyas.py
• [ ] Ask how ASM6 users expect libraries to allocate RAM
• [ ] Ask what sort of build system ASM6 users use
• [ ] Package the preprocessed code

[pinobatch]

Answers to some questions have arrived:

• Members of the NESdev Discord server recommended following the example of GGSound, which is shipped as three files: a first to include in zero page, a second one to include in BSS, and a third to include in code. The zero page and BSS files are supposed to dsb all bytes used in the library. pentlybss.py could be given this responsibility.
• Discussion in NESdev BBS showed that ASM6 users expect to break large build processes that involve time-consuming asset conversion into two build processes, one run after the other. The first converts assets; the second assembles code. The process to build Pently would run during the second.