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

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

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 3

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 4

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

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 6

7. Examples and demo Example and demo of decision structures IF THEN ELSE Set up Test condition Branch to after the code The action code ECE 3561 - Lecture 1 7

8. Example Is a > b ? a and b are memory location labels.data a.word 0x00FF b.word 0x00FF The code if a>b THEN actions cmp a,b ;computes b-a but what jump? after ECE 3561 - Lecture 1 8

9. The jumps Jump Instructions JC,Jump if carry set JHS,Jump if high or same The C bit is tested If set (i.e. 1) then the branch is taken If clear, the next instruction is executed JEQ, JZ Jump if equal, Jump if zero The Z bit is tested If set (i.e. 1) then the branch is taken If clear, the next instruction is executed ECE 3561 - Lecture 1 9

10. The Jumps (2) JGEJump if greater or equal The N and V bits are used – If N and V are set or reset (both 0 or both 1) the branch is taken JLJump if less The N and V bits are used If only one of N or V is set then the branch is taken JMP Jump unconditionally ECE 3561 - Lecture 1 10

11. Jumps (3) JNJump is negative The N bit is tested If N is set (i.e. 1) the branch is taken JNC Jump if carry not set JLOJump is lower The carry bit C is tested. If C is 0 the branch is taken JNE Jump not equal JNZ Jump if not zero The Z bit is tested If Z = 0 the branch is taken ECE 3561 - Lecture 1 11

12. A test program Write and compile a test program that sets up two values, uses cmp to compare them, and then runs through the branches. Have values that are both positive, both negative, and one positive-one negative. ECE 3561 - Lecture 1 12

13. Adding the ELSE condition If you have an else condition, set up the branch such that when the condition is not met, you have a label to branch to this code section. cmpa,b jgeelsecond ;THEN condition actions jmp ifendpt elsecond ;ELSE condition actions Ifendpt;following code ECE 3561 - Lecture 1 13

14. Repeat structures - Do Loops 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 14

15. A fix number of times For I in 1 to 10 loop action in loop End loop; Assembler Use a register for the current value of the loop counter In data area have stval – the starting value, endval – the ending value.data stval.word 0x0001 endval.word 0x000F ;loop 15 times ECE 3561 - Lecture 1 15

16. The structure ;start of loop – setup mov &stval,R8 ;i to R8 tol cmp R8,&endval jeqdone ;actions of loop incR8 jmptol done;code after loop ECE 3561 - Lecture 1 16

17. Demo Want to do loop 4 times Setup – stval of 1, endval of 4 But only execute the loop 3 times Could you solve this with the type of branch? Difficult Easy – endval is number of times through the loop + 1 OR i is one less than the iteration through the loop at compare, i.e. initial value is 0 – move inc instruction to just after the jump ECE 3561 - Lecture 1 17

18. New material - TA New material starts here ECE 3561 - Lecture 1 18

19. 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 19

20. 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 20

21. 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 21

22. 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 22

23. 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 pushR8 pushx callsmult popR8 addb,R8 movR8,A ECE 3561 - Lecture 1 23

24. 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 24

25. Assembler for example A and B are in memory Will use a register for temp. cmpA,B ;B-A is positive if A<B jlnoexch ;jump if B<A movA,R6 movB,A movR6,B noexch ECE 3561 - Lecture 1 25

26. A more efficient coding Could be made a little more efficient Previous code also exchanges when A=B cmpB,A ;A-B is negative if A<B jgenoexch ;jump if B<=A movA,R6 movB,A movR6,B noexch ECE 3561 - Lecture 1 26

27. 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 cmpB,A ;A-B is negative if A<B jgeelse ;jump if B<=A movA,R6 movB,A movR6,B jmpafter elseclrA after ECE 3561 - Lecture 1 27

28. 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 28

29. 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 tolcmpendval,R9 ;R9-endval jgelpexit movR9,R8 decR8 clrc rolcR8 add#element,R8 add@R8,sum incR9 jmptol lpexit ECE 3561 - Lecture 1 29

30. 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 30

31. The while loop example i=0; flag=TRUE; WHILE flag LOOP increment i; Actions when value i; IF i = 5 THEN flag = False; END IF; END LOOP; Now translate this to assembler ECE 3561 - Lecture 1 31

32. Assembler for while example mov#0,&i mov#1,&flag ;1=TRUE rptcmp&flag,#0 jeqdone inc&i nop;code to do actions cmp&i,#5 jnerpt mov#0,&flag jmprpt donenop;code after loop ECE 3561 - Lecture 1 32

33. ECE 3561 - Lecture 1 33 Demo Demo of loop code.