example ca65 startup code

[danwinslow]

Does anyone have an example of a stand-alone ca65 program startup using the standard atari.cfg ?

 

I took a look at crt0.s but its got a lot of stuff in there that probably isn't necessary and I'd like to get the smallest startup footprint possible.

 

Thanks

[Irgendwer]

Does anyone have an example of a stand-alone ca65 program startup using the standard atari.cfg ?

 

Attached - just changes console color to grey.

Build by 'executing' "MakeMain.bat". Since the linker likes to have some symbols, I built my own config.

Normally you have to fiddle with the config anyway to fulfil A8's memory constraints for screen, DL, font(s) and PMGs without using the dissipative .ALIGN...

MinimalASM.zip

Edited March 8, 2013 by Irgendwer

[danwinslow]

Thanks so much, Irgendwer. This is perfect.

Edited March 8, 2013 by danwinslow

[danwinslow]

More questions, if you don't mind. What you gave me seemed to work fine, although it locks up at the end due to the the endless jmp loop you put there. Not sure why you did that, but I assumed I could replace it with a rts and all would be well. So far so good.

 

Then I added some data value, with the code as such to place a 512 byte buffer somewhere:

.include "atari.inc"

.CODE
.proc Main
lda #6
sta 710
		 rts;
END:
.endproc

.SEGMENT "EXEHDR"
.word $FFFF
.word Main
.word Main::END - 1

.segment "AUTOSTRT"
.word RUNAD ; defined in atari.h
.word RUNAD+1
.word Main

.segment "DATA"
packetdata: .res 512

 

This resulted in crashes, so I tried moving it around, etc, and it always seemed to produce some kind of bad effect, either crashes or an 'error 146', which I assume to be a spurious error. So, I'm left with the impression that I don't understand something significant about how to lay out the code. The linker shows the "DATA" segment as part of RAM, which seems to be laid out correctly in the file. What am I not understanding...

Edited March 8, 2013 by danwinslow

[danwinslow]

Well, so in looking at the binary file format...the exehdr would be too short ( END would not have been incremented to include the 512 byte of data... ) and so the loader would have maybe thought the data buffer was actually an INITADR or something. So, if I locate the buffer between proc Main and END: it should work out...and it did.

 

So in this layout I'd have to place all code and data between those two spots?

[Irgendwer]

So in this layout I'd have to place all code and data between those two spots?

 

Yes, or you have to adapt "EXEHDR" end address. Since in this case CODE and DATA are consecutive, this shouldn't be a problem.

If not, you have to add an additional data segment file header for the output file too (source and memory config).

But if you like to 'reserve' just some data, BSS is better suited since it won't be written to the output file.

 

One of cc65's strongest points, but also highest entry threshold is the memory configuration. It's really the backbone of your output.

Edited March 8, 2013 by Irgendwer