1. The Stack

2. ARMSim memory space: 0x11400 + Unused 0x09400-0x11400 Stack 0x01400-0x09400 Heap 0x?????-0x01400 Data 0x01000-0x????? Text 0x00000-0x01000 Reserved

3. Stack possibilites How to use the space in stack? Grow up a)Keep track of top item in stack (Full Ascending) b)Keep track of first empty slot (Empty Ascending)

4. Stack possibilites How to use the space in stack? Grow down c)Keep track of top item in stack (Full Descending) d)Keep track of first empty slot (Empty Descending)

5. Stack possibilites ARM Convention : Full Descending R13 Holds "top" of stack

6. Push Recipe Subtract 4 from sp … 81818181 0x113F4 81818181 0x113F8 81818181 0x113FC 81818181 0x11400 ????????? sp0x11400

7. Push Recipe Subtract 4 from sp … 81818181 0x113F4 81818181 0x113F8 81818181 0x113FC 81818181 0x11400 ????????? sp0x113FC

8. Push Recipe Subtract 4 from sp STR data … 81818181 0x113F4 81818181 0x113F8 81818181 0x113FC AA 0x11400 ????????? sp0x113FC

9. Push Recipe Subtract 4 from sp … 81818181 0x113F4 81818181 0x113F8 81818181 0x113FC AA 0x11400 ????????? sp0x113F8

10. Push Recipe Subtract 4 from sp STR data … 81818181 0x113F4 81818181 0x113F8 BB 0x113FC AA 0x11400 ????????? sp0x113F8

11. Pop Recipe LDR data … 81818181 0x113F4 81818181 0x113F8 BB 0x113FC AA 0x11400 ????????? sp0x113F8

12. Pop Recipe LDR data Add 4 to sp … 81818181 0x113F4 81818181 0x113F8 BB 0x113FC AA 0x11400 ????????? sp0x113FC

13. Pop Recipe LDR data … 81818181 0x113F4 81818181 0x113F8 BB 0x113FC AA 0x11400 ????????? sp0x113FC

14. Pop Recipe LDR data Add 4 to sp … 81818181 0x113F4 81818181 0x113F8 BB 0x113FC AA 0x11400 ????????? sp0x11400

15. Push / Pop Always tear down stack in reverse order – Push A – Push B – Pop B – Pop A B Stack:AAA Time

16. Machine Push/Pop Common need : machine instructions Store Multiple to Full Descending use sp and update it (!) store r1 and r2

17. Machine Push/Pop Common need : machine instructions Load Multiple from Full Descending use sp and update it (!) load r2 then r1 (reverse order)

18. Pseudo Instructions Easier pseudinstructions: PUSH {register list} POP {register list}

19. Function Calls

20. Assembly Function Assembly Functions are branches

21. Assembly Function Assembly Functions are branches – Need to know where to return to when done!

22. Assembly Function BL label Branch and Link – Branch (change PC) – But store Store next instruction address in R14 (lr = link register)

23. Assembly Function BL label Branch and Link – Branch (change PC) – But store Store next instruction address in R14 (lr = link register)

24. Assembly Function Return – Copy lr back into pc

25. Assembly Function Return – Copy lr back into pc

26. UDiv Unsigned division function – Parameters in r0, r1 – Results in r0, r1

27. UDiv Calling from main – Parameters in r0, r1 – Results in r0, r1

28. Using Functions GetTime program – Get system time – Do lots of divisions to get Hour, Min, Sec

29. Calling Conventions

30. Calling Convetions Calling Convention – Agreement for how subroutines work How we pass info What registers we can use … – Differs between platforms, compilers, etc…

31. ARM Conventions ARM Register Conventions Register RangeUse r0-r3 -Passing parameters & results -Temporary values r4-r9 -Storing information r10-r15 Special purpose

32. ARM Conventions ARM Register Conventions Register RangeUseCallerFunction r0-r3 -Passing parameters & results -Temporary values These may get destroyed. Store/restore values if you care about them!!! Change these all you want… r4-r9 -Storing informationNo worries… If you want to use these you MUST store/restore data that was there!!! r10-r15 Special purpose Only use for intended purpose

33. ABS Absolute Value – Does what it wants with r0-r3 – Makes use of r4 and r5 – must save

34. ABS Main that calls abs – must store any r0-r3 used across function call – r4+ are safe

35. Smarter ABS If function ONLY uses r0-r3 to do work, nothing to save:

36. Smarter ABS If main only uses r0-r3 between function calls, nothing to save

37. Nested Calls

38. Real functions often call other functions:

39. Nested Calls Multiple "return addresses" needed – Proc_A needs address D – Proc_B needs address B

40. Nested Calls Multiple "return addresses" needed – Proc_A needs address D – Proc_B needs address B Store return addresses on stack

41. Calling Convention Update If function call other functions: – Save/restore your return address (lr) to stack with registers r4+

42. Calling Convention Update If function does not call others: – Don't worry… just save r4+ if needed

43. Process Review Subroutine Call (done by the caller): Subroutine Call – Push any of r0-r3 that are in use – Put argument values into r0-r3 – Call the subroutine using bl

44. Process Review Subroutine Prolog (done to start subroutine): Subroutine Prolog – If we want to use r4+ push them – If we will call other functions, push lr also – Get parameters from r0-r3

45. Process Review Subroutine Body – Use r0-r3 and any from r4+ you saved

46. Process Review Subroutine Epilog (done at end of sub): Subroutine Epilog – Put returned values in r0-r3 – Pop from the stack anything you saved (r4+, lr) – Return by moving lr to pc

47. Process Review Regaining Control (done by the caller): Regaining Control – Get results from r0-r3 – Pop any old r0-r3 values you stored before call