EE 319K�Introduction to Embedded Systems

Lecture 6b:�Exam 1 Review

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

6-1

Agenda

• Exam 1
• Exam 1, Fri 3/4 7-8:30pm.
• You MUST upload your solution by 8:30pm.

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• Topics
• Memory access
• Registers and stack
• Arithmetic operations
• Shift operations
• Logic operations
• Control structures
• Functions
• Arrays

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

6-2

Exam 1 What to study?

• Videos (posted on Canvas pages)
• 2) video on AAPCS
• 4) two videos on arrays
• Book sections 1.11, 2.4.6-2.4.10, 4.4
• eBook sections 7.5, 9.1, 9.3, 9.4, 9.5
• Worksheets
• WS_02.doc (Q4,Q5,Q6,Q10)
• WS_04.doc (Q1,Q2,Q5, Q6)
• WS_05.doc (all but Q10,Q11)
• Four practice exams
• Familiarize reference sheet/back of book

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

Do at least one to install LM3S pack

6-3

Exam 1 Process

• download zip file with project, unzip
• open project in Keil 5.x
• add your EID into code in exam1.s file
• run in simulator, see low grade
• edit exam1.s, build, debug over and over until time is up or get a 100
• Right-click the UART window, select all and execute Copy to clipboard, paste into appropriate field of the Exam 1 on Canvas.
• upload your exam1.s assembly file in the assignments section on Canvas

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

6-4

Memory Access

• Signed or Unsigned
• 8/16/32 bits
• LDRB
• LDRSB
• LDRH
• LDRSH
• LDR

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• STRB
• STRH
• STR

What do the following instructions do?

LDRH R1,[R2]

LDRH R1,[R2,#2]

LDRH R1,[R2],#2

LDRH R1,[R2,#2]!

What is the difference?

LDR R0,=100

MOV R0,#100

6-5

AAPCS, Registers and stack

• Save LR before calling another function

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• Input parameters in R0,R1,R2,R3
• Output parameter in R0
• Balance the stack
• PUSH {R4,R5} same as PUSH {R5,R4}
• Freely use R0,R1,R2,R3,R12
• Save, use, restore R4-R11

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Fun1 PUSH {R4,LR}

BL Fun2

POP {R4,PC}

Fun3 PUSH {R4-R11}

;stuff using R4-R11

POP {R4-R11}

BX LR

6-6

Arithmetic, logical, shift

ADD

SUB

SUBS

MUL

SDIV

UDIV

LSL

LSR

ASR

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AND

ANDS

ORR

BIC

EOR

How do you tell what operands are possible?

ADD R0,R1,#3

AND R0,R1,#3

MUL R0,R1,#3

UDIV R0,R1,#3

LSL R0,R1,#3

6-7

Control Operations

• If-then

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• If-then-else

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• Do-while

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• While

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CMP R0,#0

Bxx Target

CMP R0,#0

Bxx Yes

No ;not true

;

B done

Yes ;true

;

done

loop

;body

CMP R0,#0

Bxx loop

loop CMP R0,#0

Bxx done

;body

B loop

done

BEQ

BNE

BLO

BLS

BHI

BHS

BEQ

BNE

BLT

BLE

BGT

BGE

6-8

Special cases

• If-then with bit mask

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• Do-while with counter

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ANDS R0,#4

BEQ Target

ANDS R0,#4

BNE Target

loop

;stuff

SUBS R0,#1

BNE loop

6-9

Arrays

• Base
• Pointer passed in a register
• Precision
• 8 bits n=1 byte
• 16 bits n=2 bytes
• 32 bits n=4 bytes
• Size
• Fixed and known
• Passed in another register
• Value
• Character
• Unsigned integer
• Signed integer

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0 ≤ I < Size

Base+n*I

6-10

Examples

• Simple programs
• Clear, set, toggle, swap bits
• Check if a bit is high or low
• Logic, shift
• Add, sub, multiply, and divide
• Array programs
• Min, max, sum, product, difference, average
• Search for element
• Replace one element with another
• Copy from one to another

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

6-11

Strategies

• Know the inputs
• Put a breakpoint on your first line
• Look at R0, R1, … as passed to you
• Know the expected outputs
• Comments
• Grader output
• Know AAPCS
• Actually debug
• Single step your code
• Look at registers, memory
• Debug the nth call to your code
• Understand complexity
• If-then
• Single loop
• Double loop

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

6-12