C in CodeWarrior
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
1
Example
• Start up CodeWarrior and select “New Project”
– Select MC9S12C32, and “Full Chip Simulation” as usual
• Select “C” and set a project name and location
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
2
Next screen
• Select “Create main.c/main.asm file”
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
3
Next screen
• Choose “none” for device initialization
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
4
Next screen
• Choose: ANSI startup code; small memory model, no floating
point support
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
5
Last screen
• Choose “No” for lint tools
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
6
Template C Program generated by
CodeWarrior
• Don’t delete any of this
#include <hidef.h>
/* common defines and macros */
#include "derivative.h"
/* derivative-specific definitions */
void main(void) {
/* put your own code here */
If you have any functions, put them here.
Global variables can also be defined here.
Put your data declarations here
EnableInterrupts;
Infinite loop
Put any initialization code you have here
Code for your main loop goes here
for(;;) {
_FEED_COP(); /* feeds the dog */
“COP” means “computer
} /* loop forever */
operating properly” – we
/* please make sure that you never leave main */
aren’t using this
}
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
7
#include <hidef.h>
/* common defines and macros */
#include "derivative.h"
/* derivative-specific definitions */
// Initialize Table with Gray codes
char Table[] = {0x00,0x01,0x03,0x02,0x06,0x07,0x05,0x04};
int n;
void main(void) {
EnableInterrupts;
DDRT = 0x07;
n = 0;
Example:
Gray Code
output
//Set up Port T, bits 0..2, for output
/* Main loop */
for(;;) {
PTT = Table[n]; // Write next value to PortT
if (++n >= 8)
n = 0;
// Optionally delay a short time
_FEED_COP(); /* feeds the dog */
} /* loop forever */
}
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
8
10:
11:
0000
12:
13:
0002
0004
14:
0007
0008
0009
15:
16:
17:
18:
000c
000f
0013
19:
0016
0017
001a
001d
20:
001f
0020
0021
21:
22:
23:
0024
0026
0028
0029
002b
24:
25:
void main(void) {
EnableInterrupts;
10ef
[1]
CLI
DDRT = 0x07;
c607
[1]
7b0000
[3]
n = 0;
c7
[1]
87
[1]
7c0000
[3]
//Set up Port T, bits 0..2, for output
LDAB #7
STAB _DDRT
CLRB
CLRA
STD
“List” file
• Choose Project>Disassemble
n
/* Main loop */
for(;;) {
PTT = Table[n]; // Write next value to PortT
fe0000
[3]
LDX
n
e6e20000
[4]
LDAB Table,X
7b0000
[3]
STAB _PTT
if (++n >= 8)
08
[1]
INX
7e0000
[3]
STX
n
8e0008
[2]
CPX
#8
2d05
[3/1]
BLT
*+7 ;abs = 0024
n = 0;
c7
[1]
CLRB
87
[1]
CLRA
7c0000
[3]
STD
n
// Optionally delay a short time
_FEED_COP(); /* feeds the dog */
c655
[1]
LDAB #85
5b3f
[2]
STAB 63
58
[1]
LSLB
5b3f
[2]
STAB 63
20df
[3]
BRA
*-31 ;abs = 000c
} /* loop
forever
*/
Microcontroller
Architecture
and Interfacing
Colorado School of Mines
}
Professor William Hoff
9
Step one C
instruction
Step one assembly
instruction
You can see the assembly
language instructions
corresponding to the C
instructions
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
10
Analysis
• Where in memory are the variables stored?
• Where is “Table” initialized, and when?
• How fast do the Gray codes come out (# clock
cycles between codes)?
• Could you write assembly language code that is
faster?
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
11
Mixing Assembly and C Instructions
• You can use assembly language instructions inside a C program
• Just enclose the assembly instructions inside {} brackets following the
“__asm” statement
• Example: this
module
delays 10
microseconds
__asm {
; Main loop
ldx #10
loop: psha
pula
psha
pula
psha
pula
psha
pula
nop
dbne x,loop
}
Microcontroller Architecture and Interfacing
is 24 cycles, or 1 usec
; 3 additional cycles here
; 2 E cycles
; 3 E cycles
; 2 E cycles
; 3 E cycles
; 2 E cycles
; 3 E cycles
; 2 E cycles
; 3 E cycles
; 1 E cycle
; 3 E cycles
Colorado School of Mines
Professor William Hoff
12
Passing values to assembly code
• The compiler is
smart enough to
let you access
variables
defined in C, in
your assembly
code
• Example – this is
a function to
delay “t”
microseconds
Microcontroller Architecture and Interfacing
/* Subroutine DelayuSec
This subroutine delays t microsecs
(assuming a 24 MHz E clock).
*/
void DelayuSec(int t) {
__asm {
ldx t
; get number of usec to delay
; Main loop is 24 cycles, or 1 usec
loop: psha
; 2 E cycles
pula
; 3 E cycles
psha
; 2 E cycles
pula
; 3 E cycles
psha
; 2 E cycles
pula
; 3 E cycles
psha
; 2 E cycles
pula
; 3 E cycles
nop
; 1 E cycle
dbne x,loop ; 3 E cycles
}
}
Colorado School of Mines
Professor William Hoff
13
Example - Main program
void main(void) {
int i;
Note – we have to declare the local variable called
“i” here before using it below
EnableInterrupts;
/* Enable PT0 for output */
DDRT = 0x01;
for(;;) {
PTT = 0x01;
// turn on LED
// Delay for 1000x1000 us = 1.0 sec
for (i=0; i<1000; i++)
DelayuSec(1000);
PTT = 0x00;
// turn off LED
// Delay for 1000x1000 us = 1.0 sec
for (i=0; i<1000; i++)
DelayuSec(1000);
_FEED_COP(); /* feeds the dog */
} /* loop forever */
/* please make sure that you never leave main */
}
Microcontroller Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
14