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ECE/CE 3720: Embedded System Design
(ECE 6960/2 and CS 6968)
Chris J. Myers
Lecture 4: Software Development (cont)
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Modular Software Development
distinct and independent modules.Modular programming breaks software problems in
Modular software development provides:
Functional abstraction to allow software reuse.
Complexity abstraction (i.e., divide and conquer).
Portability.
A
program module
is a self-contained software task with
clear
entry
and
exit points
their entirety perform a well-defined set of tasks.Can be a collection of subroutines or functions that in
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Software Module
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Stack Contents
jsr movb ss,1,-sp ;push parameter onto stack
sqrt
;call sqrt subroutine
stab ttins
;save result
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Example Module in Assembly
sqrt pshy
leas -4,sptsy
;allocate t,oldt,s
bne nextdec cnt,ystab t,y...ldaa s8,yclrb
done tys
rtspuly
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Returning Multiple Parameters in Assembly 1
module: ldaa #
ldxldab #
ldy
rts
;returns 4 parameters in 4 registers
********calling sequence******
jsr module
- Reg A,B,X,Y have four results
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Returning Multiple Parameters in Assembly 2
module movb #2,data2,sp ;2nd parameter onto stackmodule movb #1,data1,sp ;1st parameter onto stackdata2 equ 3 data1 equ 2
rts
*******calling sequence******
pulajsr moduleleas -2,sp ;allocate space for results
;1st parameter from stack
pulastaa first
;2nd parameter from stack
staa second
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More Issues in Modular Software
stack and return parameters in the same way.All exit points in an assembly routine must balance the
harder to reuse at a later time.Performing unnecessary I/O in a subroutine makes it
of modules that can access them should be restricted.I/O devices must be considered global, and the number
Information hiding
means to separate mechanism from
policies (i.e., hiding the inner workings from the user).
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Layered Approach for Parallel Port
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Three-Layer Software System (High Level)
org
$E
main:
lds
#$00FF
bsr
Initialize ;simple call to a function
loop:
bsr
PrintInfo
;simple call to a function
bra
loop
Initialize:
ldaa #
;function code for InitPrinter
swi
;call to middle level
org $FFFErts
;high level vector (reset)
fdb
main
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Three-Layer Software System (Middle Level)
org
$F
swihandler:
cmpa #
;function code for InitPrinter
bne
notIP
bsr
InitPrinter
bra
swidone
notIP:
cmpa #
;function code for PrintInfo
bne
notPI
bsr
PrintInfo
bra
swidone
notPI:
;****error
swidone:
rti
InitPrinter: ldaa #
;function code for InitIEEE
ldx
$FF
;vector into low level
jsr
0,x
;call lower level
orgrts
$FFF
;middle level vector (SWI)
fdb
swihandler
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Three-Layer Software System (Low Level)
org
$F
lowhandler:
cmpa #
;function code for InitIEEE
bne
notInit
bsr
InitIEEE
bra
lowdone
notInit:
cmpa #
;function code for SetDAV
bne
notDAV
bsr
SetDAV
bra
lowdone
notDAV:
;rest of the functions
lowdone:
rts
InitIEEE:
;access to hardware
orgrts
$FF
; Lower level vector
fdb
lowhandler
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Layered Software Rules
- A module may not directly access any function or2. A module may call a lower-level module only using gate. 1. A module may make simple call to modules in same layer.
variable in another layer (w/o going through a gate).
- A module may not modify the vector address of another4. A module may not call a higher-level routine.
level’s handler(s).
- (Optional) All user interface I/O is in highest level unless7. (Optional) All I/O hardware access is in lowest level.6. (Optional) A module may not call farther than one level.
it is the purpose of the module to do such I/O.
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Threads
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Interrupts and Threads
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Recursion
A program segment is
reentrant
if it can be concurrently
executed by two (or more) threads.
A
recursive
program is one that calls itself.
When we draw a calling graph, a circle is formed.
Recursive subroutines must be reentrant.
void OutUDec(unsigned int number){memory, but use more stack space and are slower.Often easy to prove correct and use less permanent
if (number>=10){
OutUDec(number%10); }OutUDec(number/10);
else
OutChar(number+’0’); }
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SCI Initialization
BAUD
SCCR
SCCR
init
ldaa #$
;1200 baud
ldaa #$00staa BAUD
;mode
ldaa #$0Cstaa SCCR
;tie=rie=0,
rtsstaa SCCR2 ;te=re=
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SCI Input
SCSR
SCDR
InChar ldaa SCSR
;status
bita #$
;rdrf?
beq
InChar
ldaa SCDR
;SCI data
rts
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SCI Output
SCSR
SCDR
OutChar ldab SCSR
;status
bitb #$
;tdre?
beq
OutChar
staa SCDR
;output
rts
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Input Decimal Number
; Inputs: ; Input a byte from the SCI
none
; ; Outputs: Reg B 0 to 255
C=1 if error
DIGIT
rmb
1
;global
InUDec
clrb
;N=
InUDloop bsr
InChar
;Next input
bsr
OutChar ;Echo
cmpa #
;done if cr
beq
InUDret ;with C=
blocmpa #’
InUDerr ;error?
bhicmpa #’
InUDerr ;error?
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Input Decimal Number (cont)
anda #$0F
;0-9 digit
tstamulldaa #10staa DIGIT
;overflow?
bne
InUDerr
braaddb DIGIT ;N=10*N+DIGIT
InUDloop
InUDerr
bsrldaa #’?
OutChar
secclrb
;error flag
InUDret
rts
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SCI Output String
; Inputs: ; Output a string to the SCI
Reg X points to string
String ends with 0
OutString ldaa 0,X; Outputs: none
beq
OSdone
;0 at end
bsr
OutChar
brainx
OutString
OSdone
rts
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SCI Output Decimal Number
; Inputs: ; Output unsigned byte to the SCI
Reg B= 0 to 255,
print as 3 digit ascii
OutUDec; Outputs: none
clra
;Reg D=number
ldx
idiv
;X=num/100,
xgdx
;B=100s digit
bsradda #’0 ;A=100’s asciitba
OutChar
xgdx
;D=num
ldx
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SCI Output Decimal Number (cont) idiv
;X=num/10,
xgdx
;B=tens digit
bsradda #’0 ;A=tens asciitba
OutChar
xgdx
;D=num
bsradda #’0 ;A=ones asciitba
OutChar
rts
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Performance (Dynamic) Debugging
Performance debugging
is verification of timing behavior.
System is run and dynamic behaviors of I/O checked.
- Instrumentation: measuring with a counter.1. Count bus cycles using the assembly listing.
before
rmb
2
;TCNT value before the call
elasped rmb
2
;# of cycles to execute sqrt
movw
TCNT,before
movb
ss,1,-sp
;push parameter on stack
jsr
sqrt
;call sqrt module
stabins
tt
;save result
ldd
TCNT
;TCNT value after the call
subd
before
std
elasped
;execute time in cycles
- Instrumentation: output port.
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Profiling
Profiling
collects time history of strategic variables.
- Use an output port.1. Use a software dump to study execution pattern.
techniques to determine the thread activity.When multiple threads are running can use these
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