ECE 4436 Microprocessor Systems

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ECE 4436Microprocessor Systems

• Monday February 12, 2001
• Week 05 Lecture 08

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Todays Agenda

• Annoucements/News
• HW4
• Midterm ? Wednesday, February 28th!
• SPIM demo
• Assign Lab 1
• C Declarations Copies
• Flow Control Instructions
• For While Loops Using Arrays
• Handout on Loops

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C Declarations Copies

• char a 0xAB
• char b 0
• unsigned char c 0xA0
• short int d 0xABCD
• short int e 0
• unsigned short int f 0xABC0
• int g 0x89ABCDEF
• int h 0
• unsinged int i 0x89ABCDE0

• a _____ 0xAB
• b _____ 0
• c _____ 0xA0
• d _____ 0xABCD
• e _____ 0
• f _____ 0xABC0
• g _____ 0x89ABCDEF
• h _____ 0
• i _____ 0x89ABCDE0

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C Declarations Copies
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C Declarations Copies

• b a
• LB t0,a char ? char
• SB t0,b
• h f
• LHU t0,f int ? unsigned short int
• SW t0,h
• h g
• LW t0,g int ? int
• SW t0,h

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C Declarations Copies

• i 0xABCD
• LI t0,0xABCD
• SW t0,i
• g i
• LW t0,i overflow error if i ? 0x80000000
• SW t0,g int ? int unsigned
• e a
• LB t0,a short int ? char
• SH t0,e
• b f
• LHU t0,f overflow error
• SB t0,b if f ? 0x80

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Flow Control Instructions

• Unconditional transfer of control.
• Conditional transfer of control.
• A label in used to indicate the target of a
  branch, jump or subroutine call.

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Unconditional Branch

• J label
• transfer control unconditionally to instruction
  following label
• Ex.

loop add t1,s3,s3 sw t1,8(s4) j loop
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Conditional Branches

• BEQ R1,R2,label
• compare R1 and R2. If , transfer control to
  label. If ? execute next instruction.
• Ex. BEQ t1,t2,exit
• BNE R1,R2,label
• take branch if R1 ? R2
• Ex. BNE t1,t2,loop

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Conditional Branches

• 10 Conditional Branches
• BEQ () BNE (!)
• BLT (lt) BLTU
• BLE (lt) BLEU
• BGT (gt) BGTU
• BGE (gt) BGEU
• Ex.
• is 11112 greater than 00002?

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Conditional Branches

• Also have some pseudoinstructions
• BEQZ BLTZ BGTZ
• BNEZ BLEZ BGEZ
• Ex
• BEQZ t0,label7 take branch if t00

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Conditional Branches

• Ex 1
• Ex 2

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Conditional Branches

• Ex 3

if (ij) ff-i else fgh
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Branch Formats

• Jump is a J-type instruction
• Conditional Branches are I-type instructions

op
target addr. / 4
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For While Loops Using Arrays

• Ex. clear an uninitialized array
• int arrayA100
• for (i0 ilt100 i) arrayAi 0
• Let
• i s3
• base addr. of A s4
• 100 t1

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For While Loops Using Arrays
.data arrayA .space 400 .text LI t1,100
load count MOVE s3,zero i
0 LA s4,arrayA load addr. of
A LOOP BGE s3,t1,DONE done? ADD t2,s3,s3
i ? 2 i ADD t2,t2,t2 double
again ADD t2,t2,s4 ArrayAi SW zero,0(t
2) ArrayAi ADD s3,s3,1
i J LOOP DONE
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See Handout on For While Loops!
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Assignment for Wednesday

• Check web for slides
• Study for Quiz on Wednesday!
• Play with SPIM
• Start Lab 1!
• Read PH 3.5, handout

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Scratch Pad