Chances are, most of your project's code could be written in C without a significant performance or size penalty. Some timing-critical or speed-critical routines may require the precision of assembly coding, but these sections of code are few and far between. If you want to use C code on your HC11 microcontroller, read on...

The compiler we recommend is Dunfield Micro C (available from the TAs and Tom). This compiler is written by the same guy who wrote the asm11 assembler mentioned in the HC11 Dunfield Quickstart. The Micro C compiler is NOT an ANSI C compiler, though it is close. It supports one-byte and two-byte integers natively, with larger numbers available if you use special routines. Floating point is not supported. However, all the standard control structures (if, case, while, for, etc.) are fully implemented, along with basic math (+,-,*,/,%,etc.) and logic (&,|,^,etc.). Refer to the MICRO-C documentation for more information about these things.

Compiler Configuration
Before you start coding, there are a few Dunfield files that you'll have to modify. These files specify where your stack will be located, where RAM and ROM start, and other things that the compiler needs to know in order to map your code to your memory space.

In the MC\LIB11 directory, open 6811RLM.ASM. The very bottom of the file looks like this:

6811RLM.ASM
*#map2 Set address of un-initialized variables
* Set up the origin of external RAM based variables.
* Eliminate this statement if you are NOT using external RAM
* and want all variables allocated in internal RAM.
*
	ORG	$4000		External RAM begins here

Next, open 6811RLP.asm. The first few lines are:

6811RLP.ASM (original)
?REGS	EQU	$0000		68HC711D3 internal registers
?parm	EQU	$0040		Parameter to runtime library
?temp	EQU	?parm+2		Temporary register
	ORG	$0100		Place code in memory here
?begin	LDS	#$7FFF		Initial stack goes here

6811RLP.ASM (modified)
?REGS	EQU	$1000		68HC11E0 internal registers
?parm	EQU	$0000		Parameter to runtime library
?temp	EQU	?parm+2		Temporary register
	ORG	$8000		Place code in memory here
?begin	LDS	#$7FFF		Initial stack goes here

Preliminary Programming
Now that the environment is set up correctly, you can try writing and compiling a simple program. This program, for example, prints "Hello World!" to the serial port and then blinks an LED connected to Port X, Pin Y. I'll call this one hello.c:

hello.c
#include <6811reg.h>
#include <6811io.h>		// MUST be included to use printf, sprintf, concat
int main()
{
	unsigned char temp;
	BAUD = 0x30;	// 9600b
	SCCR1 = 0x00;	// 8-bit mode
	SCCR2 = 0x0C;	// enable Tx/Rx, no interrupts

	printf("Hello, world!\n");

	temp = 0;
	while(1)
	{
		if(temp%2)
			PORTA = PORTA | 0x10;		// turn on Port A, pin 4
		else
			PORTA = PORTA & ~(0x10);	// turn off Port A, pin 4
		temp++;
	}
	return 0;
}

C:\MC\mcp hello.c hello.tmp -l -c l=C:\MC                      // the preprocessor
C:\MC\mcc11 hello.tmp hello.asm -l -c -s                       // the compiler
del hello.tmp                                                  // remove the temp file
C:\MC\slink hello.asm hello.tmp l=C:\MC\lib11 i=extindex.lib   // the linker
C:\MC\asm11 hello.tmp -f                                       // the assembler
del hello.tmp                                                  // remove the temp file

Now, you should have three new files: hello.asm, hello.hex, and hello.lst. Hopefully, no errors were reported. Open up hello.lst and scroll through it. You can see how your code starts at 0x8000 and goes through approximately 0x8276 (~630 bytes). You can now take the hex file and burn it to a Flash or EPROM and run it on your board.

Tricky Things and Other Tips
The Dunfield compiler has a few quirks that you should be aware of. A more complete listing is in the MICRO-C documentation.

1. When using printf/sprintf/concat, you MUST '#include <6811io.h>'.
   (If you don't include this file, your code will compile normally, but the printf instructions will produce garbage.)
2. Watch your usage of signed/unsigned variables.
   (I suggest declaring all your chars and ints as unsigned, unless you have a specific reason not to. When doing math with signed and unsigned variables, you have to be careful. Refer to the quirks section of the manual for more specifics.)
3. Initializing at declaration time makes a constant.
   (Saying 'char a = 0;' will cause 'a' to be placed in ROM, meaning you will never be able to change 'a' to any other value. If you want to be able to modify 'a', break the above statement into two lines: 'char a; a = 0;'.)
4. Docmentation
   (Dave Dunfield has documented almost every aspect of his program. Take the time to read through the MICRO-C documentation. At the very least, go to them first when you think you've found a compiler bug. Chances are, he's already written about your issue.)
5. Libraries
   (Micro C has a nice set of libraries that you can use. Read the MICRO-C documentation on the libraries and be amazed! You will save a lot of time if you use his hand-optimized routines instead of trying to write and debug your own.)
6. printf vs. putstr
   (If you do not need the formatting capabilities of printf (e.g. printf("%u.%u",a,b)) then you should use putstr(). This is another library function, and is much quicker and less memory-intensive than printf.)