Date: Fri, 18 Feb 94 12:08:58 EST
Message-Id: <9402181642@bernard>
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From: froula@bernard.cig.mot.com (Don Froula)
To: Multiple recipients of list <robot-board@oberon.com>
Subject: minilib without C

I'm sure someone has thought of this before, but I thought I'd mention the idea.
The minilib.s library functions, that were written for use with C compilers, can
also be used quite nicely as a basis for stand-alone assembly programs.

The basic changes needed are:

	1.) Rename the minilib.s file to minilib.asm
	2.) Remove or comment out the two lines containing SECT
		assembler directives.  The Motorola assembler
		will choke on these.
	3.) Remove the lines containing the instructions:

			JSR	_main
		exit	bra	exit

	4.) Substitute your own code loop in place of these lines, right after 
		the line containing the CLI (interrupt enable) instruction.

All library function parameters are passed on the stack as 16 bit integers.
To call a library function, push the values on the stack, then JSR to the
label of the desired function.  Remember, the parameters are still on the stack
after the function returns to your code.  Be sure to restore the stack pointer,
or you'll run out of stack ram in a hurry!  Also, functions that take more than
one argument must be pushed onto the stack in reverse of the "C" argument
order.

For example, the C function call "motor(1,8)" will turn on motor 1 in the
forward direction at half speed (level "8").  To do this in your minilib
assembly loop:

	LDX	#8	*Motor speed and direction (SECOND parameter in C code)
	PSHX		*Push motor speed and direction to stack
	LDX	#1	*Motor number (FIRST parameter in C code)
	PSHX		*Push motor number to stack
	JSR	_motor	*Call the function
	PULX		*Remove both numbers from the stack after call returns
	PULX

For functions with no arguments, just JSR to the function.  

Assembly labels for the functions are all "_<function>", so the label for 
"int analog(int port)" is "_analog".

Functions that return integers return them as an 8 bit value in the B
accumulator.

I got my first application running in less than 30 minutes!