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L11-HLL to Assembler

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  1. ECE 2560 L11-HLL to Assembler Department of Electrical and Computer Engineering The Ohio State University ECE 3561 - Lecture 1

  2. HLL to Assembler • Pseudo HLL • HLL structure • Their flow chart • HHL code • Corresponding Assembler ECE 3561 - Lecture 1

  3. What is Pseudo HLL • Pseudo HLL is a way of expressing an algorithm or procedure for performing a task. • Very similar to modern High Level programming Languages • Best illustrated with an example ECE 3561 - Lecture 1

  4. Pseudo HLL example • Sum a list of 10 integers • 3 7 8 2 4 6 5 5 9 1 • There are several methods • The algorithm here • Create sum and initialize to 0 • Add first number • Repeat adding number until done with list ECE 3561 - Lecture 1

  5. Pseudo HLL • Sequence of Actions • Do action A • Do action B • …. • Do action Q ECE 3561 - Lecture 1

  6. Decisions • Decision structures • IF condition THEN action if true • ELSE action if false • END IF; • Example: • Remove front bike wheel • TURN Bike over • IF wheel-has-quick-release-skewer • THEN flip level and remove wheel • ELSE use wrench to remove nuts from axle • remove wheel • END IF ECE 3561 - Lecture 1

  7. Repeat structures • Finite number of times – DO LOOP • Set up any values for loop • FOR counter = start TO end [STEP x] LOOP • actions of loop • END FOR; • Example: • Sum = 0; • FOR i = 1 to 10 LOOP • Sum = Sum + element(i); • END FOR; ECE 3561 - Lecture 1

  8. Repeat structures • Indeterminate number of times – Repeat loop or decision loop – action inside the loop causes condition to occur that ends the loop. • 2 structures • One has code that executes at least once • One has code that may or may not execute at all ECE 3561 - Lecture 1

  9. While condition • While loop – may or may not execute code • WHILE condition LOOP • SEQUENCE_of_ACTIONS • END loop; • Example: • WHILE not EOF LOOP • Read line from file • Process line • END LOOP; ECE 3561 - Lecture 1

  10. Repeat • Repeat Until structure • REPEAT • Sequence_of_statements • UNITL condition; • Example - attempt to read will be done at least once • REPEAT • Read line from file • UNTIL EOF; ECE 3561 - Lecture 1

  11. Now what is the assembler? • For each of these Pseudo HLL structures what is the corresponding assembler. • Each will have assumption as to were data to be tested is. ECE 3561 - Lecture 1

  12. Straight line code - Sequence • Straight line Pseudo HLL – little modification is needed. • A = m*x + b in Pseudo HLL • Where are values – say in memory locations labeled by the same name • Code becomes • mov m,R8 • push R8 • push x • call smult • pop • pop R8 • add b,R8 • mov R8,A ECE 3561 - Lecture 1

  13. Decision • Decision structure • IF condition THEN action if true • ELSE action if false • END IF; • Example: • IF (A<B) THEN temp=A; A=B; B=temp • END IF; ECE 3561 - Lecture 1

  14. Assembler for example • A and B are in memory • Will use a register for temp. • cmp A,B ;B-A is positive if A<B • jl noexch ;jump if B<A • mov A,R6 • mov B,A • mov R6,A • noexch ECE 3561 - Lecture 1

  15. A more efficient coding • Could be made a little more efficient • Previous code also exchanges when A=B • cmp B,A ;A-B is negative if A<B • jgenoexch ;jump if B<=A • mov A,R6 • mov B,A • mov R6,A • noexch ECE 3561 - Lecture 1

  16. When there is an else • Else is similar to the previous code • IF (A<B) THEN temp=A; A=B; B=temp; • ELSE A = 0; • END IF; • Much like previous • cmp B,A ;A-B is negative if A<B • jge else ;jump if B<=A • mov A,R6 • mov B,A • mov R6,A • jmp after • else clr A • after ECE 3561 - Lecture 1

  17. Repeat structures • Finite number of times – DO LOOP • Set up any values for loop • FOR counter = start TO end [STEP x] LOOP • actions of loop • END FOR; • Example: • Sum = 0; • FOR i = 1 to 10 LOOP • Sum = Sum + element(i); • END FOR; • How would this example be coded? ECE 3561 - Lecture 1

  18. Coding for Do Loop • Where are control values? • i – the current index value – use R9 • startval – the starting value for i – memory loc • endval – the ending value for i – memory • sum – in memory • element – label of list of values in memory • mov i,R9 • tolcmp endval,R9 ;R9-endval • jgelpexit • mov R9,R8 • dec R8 • clrc • rolc R8 • add #element,R8 • add @R8,sum • inc R9 • jmptol • lpexit ECE 3561 - Lecture 1

  19. The repeat and while loops • The coding of the repeat and while loops is very similar. • Documents where variables are • Need loop control and testing of loop control • Which branch instruction to use takes some thought • Need to remember what the cmp instruction does!! ECE 3561 - Lecture 1

  20. Summary - Assignment • No new assignment. ECE 3561 - Lecture 1

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