How do I get CC65 to include NO startup code?

[Mike]

try with -Osir the generated code is large in some cases, but its not *that* bad really

Now that's really funny. With a slightly trimmed version of 'main.c' ...

Code: Select all

typedef unsigned char byte;

#define SCREEN_ADDR   (0x1E00)
#define COL_ADDR      (0x9600)

void main()
{
    *((byte *)(SCREEN_ADDR+1)) = 0x01;
    *((byte *)(COL_ADDR+1)) = 0x02;
    
    *((byte *)(SCREEN_ADDR+2)) = 0x02;
    *((byte *)(COL_ADDR+2)) = 0x03;

    loop: goto loop;
}

... and using 'cc65 -t none -Osir' it's actually possible to coerce cc65 into producing the desired output:

Code: Select all

;
; File generated by cc65 v 2.13.2
;
	.fopt		compiler,"cc65 v 2.13.2"
	.setcpu		"6502"
	.smart		on
	.autoimport	on
	.case		on
	.debuginfo	off
	.importzp	sp, sreg, regsave, regbank, tmp1, ptr1, ptr2
	.macpack	longbranch
	.forceimport	__STARTUP__
	.export		_main

; ---------------------------------------------------------------
; void __near__ main (void)
; ---------------------------------------------------------------

.segment	"CODE"

.proc	_main: near

.segment	"CODE"

	lda     #$01
	sta     $1E01
	lda     #$02
	sta     $9601
	sta     $1E02
	lda     #$03
	sta     $9602
L0017:	jmp     L0017

.endproc

Not bad.

Maybe I'm just used to a C programming style that doesn't want to miss out on the standard library functions. On non-65xx platforms, that is. Of course C always offers you to create an own library, when the supplied implementation doesn't suit you.

[groepaz]

oh, actually even with cc65 it is a very good idea to use the standard library as often as possible (usually the generated code will be smaller and faster than doing the same stuff inline) - however, its also a good idea to think twice about what you are using. as said malloc is often not a good idea and static buffers work better (as in: smaller footprint). also avoiding things like printf (because printf is actually file i/o, it pulls in tons of stuff - better use conio). those things are common things to do on other embedded platforms as well

[JavaJack59]

I could do with some tips on converting the jiffy clock to integers 0-9. I'm assuming there's something in ROM that can do this for me ("print ti$") but I don't know how to make use of it.

[Mike]

I could do with some tips on converting the jiffy clock to integers 0-9. I'm assuming there's something in ROM that can do this for me ("print ti$") but I don't know how to make use of it.

I suppose you overlooked that reply:

A digital clock program. Read the jiffy clock and display it [...]

In that case, the thread 'Display of TI$ in border (unex. or +3K)' might be worth a look.

And yes, there's a routine in ROM to do the same. However, that routine relies on float and string operations and requires one to set up a lot of zeropage locations, and memory areas in a certain way to operate correctly.

Anyway, it should not be too difficult to infer from the disassembly how my own implementation of the conversion works. The jiffy clock is a 24-bit number, and it is incremented by one every 1/60 second (and reset to 0 as it reaches 24:00:00). There's a table with tens of hours, then hours, tens of minutes, minutes, tens of seconds and seconds in jiffies, which are (in that order) subtracted off a copy of the jiffy clock until the respective digit underflows to obtain a string equivalent to TI$ - which however is directly written to a part of the extended screen unreachable by the editor.

OTOH, there's always 'time.h' in the standard library, where time(), localtime() and asctime() also should be able to do the job.

[JavaJack59]

subtracted off a copy of the jiffy clock until the respective digit underflows

Yeah, I did read it, but it wasn't immediately obvious to me how to translate it into vanilla C, since it relied on lower level things like the CPU overflow flag.

[JavaJack59]

A "while greater than, subtract" loop seems to work.

It took me a while to figure out that I couldn't just copy the clock bytes to a long variable as-is. I had to reverse them because of little-endianness.

[JavaJack59]

Success:
http://www.wookilar.com/vic/clock.prg
http://www.wookilar.com/vic/clock.zip

[beamrider]

Nice. Good to see an example in 'c' for the vic.

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