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EE 319K�Introduction to Embedded Systems

Lecture 3: C programming

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Agenda

Recap

Variables
Functions

Parameters
Prototypes, Implementation, Invocation

Outline

Overflow (add/sub, mult, divide)
Application of arrays
Arrays

Index
Pointer

Debugging

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

n+n => n+1

n-n => n+1

n*n => 2n

n/n => n

Review prime pi examples from EE312H

Header file
Code file
Testmain file

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IR distance sensor

#define K1 1195172

#define K2 -1058

int32_t IRconvert(int32_t n){

return K1/(n + K2);

}

int32_t IRconvert2(int32_t n){

int32_t d;

if(n<3000) return 800;

if(n>13000) return 100;

d = K1/(n + K2);

return d;

}

d = 1195172/(n – 1058 )

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Arrays

Definition (type, size, allocation)

#define LEN 10

int16_t Data[10]; // global RAM

const int16_t Prime[5]={2,3,5,7,11}; // global ROM

void fun(void){ char name[8];

}

Index access

Data[0] = 55;

Data[1] = 72;

Zero index address calculation Buf[i]

32 bit: Buf+4*i

16 bit: Buf+2*i

8 bit: Buf+i

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Array example

Definition (type, size, allocation)

#define LEN 10

int32_t aa[LEN];

int32_t bb[LEN];

Access

int32_t s=0;

for(int32_t i=0;i<LEN;i++){

s += aa[i]*bb[i];

}

Review: what is?

aa[0]

&aa[0]

aa

aa[i]

*aa

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Array parameters

Parameter is pass by reference

int32_t dot(int32_t a[], int32_t b[], int32_t l){

int32_t s=0;

for(int32_t i=0;i<l;i++){

s += a[i]*b[i];

}

return s;

}

Invocation pass by reference

int main(void){

int32_t result;

result = dot(aa,bb,5);

while(1){

}

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

s RN 4

i RN 5

dot

MOV s,#0 ;s=0

MOV i,#0 ;i=0

forloop3

CMP i,R2 ;is i<l

BGE forDone3

ASL R6,i,#2 ;i*4

LDR R7,[R0,R6]

LDR R8,[R1,R6]

MUL R7,R7,R8

ADD s,s,R7

ADD i,i,#1

B forloop3

forDone3

MOV R0,s

BX LR

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Thermodilution

uint32_t T[1000];

// temperature in C

// 100 Hz, 10 sec

#define K3 43660

uint32_t CardiacOutput(void){

uint32_t sum,i,CO;

sum = 0;

for(i=0; i<1000; i++){

sum = sum+T[i];

}

CO = K3/sum;

return CO;

}

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Maximum of an array

int32_t max(int32_t data[],

uint32_t size){

int32_t ans,i;

ans = data[0]; // assume first is max

for(i=1; i < size; i++){

if(data[i] > ans){

ans = data[i];

}

return ans;

}

#define SIZE 10

int32_t MyData[SIZE];

int main(){int32_t myMax;

while(1){

// fill up MyData

myMax = max(MyData,SIZE);

}

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Dot product

int32_t dot(int32_t a[], int32_t b[],

int32_t length){ int32_t s=0;

for(int32_t i=0;i< length;i++){

s += a[i]*b[i];

}

return s;

}

#define LEN 5

int32_t aa[LEN];

int32_t bb[LEN];

int main(void){

int32_t result;

for(int i=0; i< LEN;i++){

aa[i] = i;

bb[i] = 5;

}

result = dot(aa,bb,LEN);

while(1){ }

}

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Capitalize letters in string

char name[10] = "Jonathan";

// uncapitalize every letter

void uncap(char str[]){int i=0;

while(str[i]){

str[i] |= 0x20;

i++;

}

void uncap(char *p){

while(*p){

*p |= 0x20;

p++;

}

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Debugging

Black box testing

Inputs
Outputs

White box testing

Debug individual into pieces
Control/observe internal

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Debugging

Testing, Diagnostics, Verification, Validation
Debugging Actions

Functional debugging, input/output values
Performance debugging, input/output values with time (how fast does it execute)
Resource debugging, I/O values w/ time and resources (how much memory, power, …)

Regression Testing

test recent change to existing system

full or partial selection of already executed test cases

Tracing, measure sequence of operations
Profiling,

measure percentage for tasks,
time relationship between tasks

Optimization, make tradeoffs for overall good

improve speed,
improve accuracy,
reduce memory,
reduce power,
reduce size,
reduce cost

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Debugging

Control

Breakpoints
Step

Single Step, StepOver, StepOut

Run, Run to Cursor
Test one piece at a time

Stabilization

Observability

Debugger windows

Registers including xPSR
Memory
Watch Windows
Logic Analyzer,
GPIO Panel

Output (LEDs, LCD, printf)

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Debugging Intrusiveness

Intrusive Debugging

degree of perturbation caused by the debugging itself
how much the debugging slows down execution

Non-intrusive Debugging

characteristic or quality of a debugger
allows system to operate as if debugger did not exist
e.g., logic analyzer, ICE, JTAG

Minimally intrusive

negligible effect on the system being debugged
e.g., dumps(ScanPoint) and monitors

Highly intrusive

print statements, breakpoints and single-stepping

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Tiwari

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Lab 2 demo

Advice for debugging

Observe locals and globals

Single step

Breakpoints

Example of testing

How does the grader work?

Is it exhaustive?

Bard, Erez, Gerstlauer, Holt, Valvano, Yerraballi, Telang, Cuevas, Tiwari

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Summary

Variables

Type
Size
Scope
Allocation

Functions

Declaration

Implementation
Innovation

Arrays
Debugging

Header file
Code file
Testmain file

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