CodeWarrior
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
1
Assembler
• An “assembler” is a program that translates “assembly
language” into “machine code”.
– “Machine code” are the numbers that the CPU
recognizes as instructions.
$B6 $10 $00
– “Assembly language” is a mnemonic (symbolic)
representation of machine code, purely for human
reading.
Assembly
program
Assembler
(on PC)
Machine
code
“Assembly time” or
“compile time”
Microcomputer Architecture and Interfacing
Colorado School of Mines
LDAA $1000
Target Hardware
(microcontroller)
“Run time”
Professor William Hoff
2
CodeWarrior
• CodeWarrior is an integrated development environment (IDE)
– Free version from Freescale, Inc
• Get this version: “Special Edition: CodeWarrior for HCS12(X)
Microcontrollers (Classic).”
• http://www.freescale.com/webapp/sps/site/overview.jsp?code=CW_SPECI
ALEDITIONS&fsrch=1&sr=1&pageNum=1.
• Has editor, simulator; interfaces to target hardware, debugger
– Assembler and C compiler
• We will use in class and lab
• Tutorial in section 3.8 in the book
• Approach
– You create a “project”
– This organizes all your files
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
3
Example
• Start Codewarrior
• On startup screen, choose “Create New Project”
• On next screen
– Select HCS12->HCS12C Family->MC9S12C32
– Select “Full Chip Simulation”
– Hit Next
• On next screen
– Uncheck C, check “Absolute assembly”
– Enter (or browse to) the new directory location for the
project
– Enter project name (you can leave it as “Project.mcp”)
– Hit Finish
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
4
Template Assembly file
• CodeWarrior automatically creates a sample
“main.asm” file
– This is a simple program to generate Fibonacci numbers
– You can run this program as is, or modify it
– It has some useful initialization stuff in there
• We’ll first run it as is, then change it
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
5
Header comments
main.asm
Declarations
Variables in
RAM
Initialization
Main body
of program
Interrupt
vectors Architecture and Interfacing
Microcomputer
Colorado School of Mines
Professor William Hoff
6
Assemble and Debug
•
Select Project->Compile
– If there are errors you will get a popup screen
•
Select Project->Debug
– This will bring up the debugger window
Shows
assembly code
with addresses
Source
code
CPU
registers
Contents of
memory
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
7
Running the template program
• Hit “Single Step” to step through the program
– Notice the registers changing
• Notice count of
CPU cycles
• Right click in the
Memory window and
select “Address…”
• Type 800 and hit OK
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
8
Simple Fibonacci Program
• We’ll create a simple program to generate Fibonacci numbers
– (Actually, the template program does this, but our program is simpler)
• Fibonacci numbers are a sequence defined by
Fn = Fn-1 + Fn-2
• where
F0 = 0 and F1 = 1
• The sequence is
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ...
• We will have three memory locations labeled N1,N2,N3
• These correspond to Fn-2, Fn-1, Fn
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
9
Simple Fibonacci Program
• Replace the lines
Counter
FiboRes
DS.W
DS.W
1
1
• with
N1
N2
N3
DS.B 1
DS.B 1
DS.B 1
•
•
These define labels N1,N2,N3
“DS.B 1” means “define storage
(bytes)” and the number of bytes
allocated is 1
• Replace everything between “mainloop” and “RTS” (including those lines)
with:
movb
movb
#0,N1
#1,N2
ldaa
adda
staa
N1
N2
N3
movb
movb
N2,N1
N3,N2
Initialize the first two Fibonacci numbers to be 0, 1
loop
Labels
must
start in
column
1
bra
loop
Microcomputer Architecture and Interfacing
Add N1+N2, result in N3
Save N2 and N3 as the last two values generated
Loop forever
Colorado School of Mines
Professor William Hoff
10
Simple Fibonacci Program
• Compile and run debugger
• Step through program and verify that the
Fibonacci numbers are produced in N3:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ...
• When does overflow occur?
• Number of clock cycles in the loop?
loop
– Can look up the count for each instruction, in
the instruction set table
– Or you can look at the count of CPU cycles in
the simulator as you step through
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
ldaa
adda
staa
N1
N2
N3
movb
movb
N2,N1
N3,N2
bra
loop
11
Other Assembler Details
• Comments
– Start with semicolon
– Ignored by assembler
– Example
ldaa N
; this is a comment
• Syntax for numeric constants
– $ indicates hexadecimal (e.g., $10 has decimal value 16)
– % indicates binary value (e.g., %100000 has decimal value 32)
– A number with no preceding symbol is decimal
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
12
Assembler Directives: “org”, “equ”
• These are instructions for the assembler only, not the target hardware
• These are used at “assembly time”
• They are not instructions that will be performed at “run time”
• org expr
– Tells the assembler to set the load counter to expr, the value of the operand expression
– Example
org
$1000
ldab
#$FF
– The next item to be placed in memory (the opcode byte for “ldab”) will go into $1000
• label equ expr
– The label symbol is assigned the value of expr rather than the current load counter value
– Does not allocate any space
– Example
loop_cnt
equ
$40
– From now on, whenever the symbol loop_cnt is seen, the assembler replaces it with $40
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
13
; Include derivative-specific definitions
INCLUDE 'derivative.inc'
ROMStart
EQU $4000 ; absolute address to place my code/constant data
; variable/data section
• Assemble “simple Fibonacci”
program
• Look at output list file (choose
Project->Disassemble)
ORG RAMStart
; Insert here your data definition.
N1
DS.B 1
N2
DS.B 1
N3
DS.B 1
; code section
ORG
Entry:
_Startup:
LDS
ROMStart
#RAMEnd+1
CLI
; initialize the stack pointer
; enable interrupts
movb
movb
#0,N1
#1,N2
ldaa
adda
staa
N1
N2
N3
movb
movb
N2,N1
N3,N2
bra
loop
loop
;**************************************************************
;*
Interrupt Vectors
*
;**************************************************************
ORG
$FFFE
DC.W Entry
; Reset Vector
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
14
Assembler list file
Memory Contents
address or value
:
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
5492
40
0000 4000
ROMStart
EQU
$4000
; absolute address to place my code/constant data
; variable/data section
ORG RAMStart
; Insert here your data definition.
N1
DS.B 1
N2
DS.B 1
N3
DS.B 1
a000800
a000801
a000802
; code section
ORG
ROMStart
Notes:
• DS.B just defines storage
space; it doesn’t put
anything into memory
• “movb” has a two byte
opcode
• “cli” actually is
implemented as “andcc
#$FE”
Entry:
_Startup:
a004000 CF10 00
LDS
a004003 10EF
CLI
a004005
004009
a00400A
00400E
movb
#0,N1
movb
#1,N2
180B 0008
00
180B 0108
01
Microcomputer Architecture and Interfacing
#RAMEnd+1
; initialize the stack pointer
; enable interrupts
Colorado School of Mines
Professor William Hoff
15
Assembler list file (continued)
5493
5494
5495
5496
5497
5498
5499
41
42
43
44
45
46
47
5500
48
5501
49
loop
a00400F B608 00
a004012 BB08 01
a004015 7A08 02
ldaa
adda
staa
N1
N2
N3
a004018
00401C
a00401E
004022
movb
N2,N1
movb
N3,N2
bra
loop
180C 0801
0800
180C 0802
0801
Freescale HC12-Assembler
(c) Copyright Freescale 1987-2010
Abs. Rel.
---- ---5502
50
5503
51
5504
52
5505
53
5506
54
5507
55
5508
56
5509
57
5510
58
Loc
Obj. code
------ --------a004024 20E9
a00FFFE 4000
Source line
-----------
Notes:
• The value of “loop” is
$400F
• The offset for “BRA” is
$E9 or -23 decimal
• The value $4000 is
loaded into memory at
$FFFE, $FFFF
;**************************************************************
;*
Interrupt Vectors
*
;**************************************************************
ORG
$FFFE
DC.W Entry
; Reset Vector
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
16
Summary
• The assembler translates assembly language into
machine code.
• There are special “assembler directives” that are used
at assembly time.
– Examples: org, equ, ds.b, ...
– They tell the assembler where to load the machine code,
how much storage to allocate, etc.
• Codewarrior
– An integrated development environment (IDE)
– Includes editor, assembler, C compiler, simulator
Microcomputer Architecture and Interfacing
Colorado School of Mines
Professor William Hoff
17