Page 403 - Programming Microcontrollers in C

388 Chapter 7 Advanced Topics

0, /* Timer channel 6 */
0, /* Timer channel 5 */
0, /* Timer channel 4 */
0, /* Timer channel 3 */
0, /* Timer channel 2 */
0, /* Timer channel 1 */
0, /* Timer channel 0 */
0, /* Real time */
0, /* IRQ */
0, /* XIRQ */
0, /* SWI */
0, /* illegal */
0, /* cop fail */
0, /* cop clock fail */
_stext /* RESET */
};
Listing 7-18: M68HC912B32 Vector Table

Listing 7-19 shows the next function that must be included for
operation on the M68HC12. This start-up program is named crts.s.
The .s extension indicates that the function is an assembly language
function. This is the sum total of all assembly code needed for the
program discussed in this chapter. Rather than give a line-by-line
description of the code, we will see that the initial portion of the
program initializes the section named bss to all zeros. This section
is where all static and external memory are stored. Then the stack
pointer is initialized to the value designated as __stack and then
control is passed to the function main(). If main() should return,
which it should not, the instruction following main() forms an
infinite loop that branches to itself and does nothing.

; C STARTUP FOR MC68HC12
; Copyright (c) 1996 by COSMIC Software
;
xdef _exit, __stext
xref _main, __sbss, __memory, __stack
;
__stext: