1. Subroutines and Stacks Lecture L3.1

2. Subroutine and Stacks The System Stack Subroutines A Data Stack

3. The System Stack

4. Pushing D on the stack

5. 1: ; System stack 2: =00004000 ORG $4000 3: 4000 CF 08FF LDS #$08FF 4: 4003 CC 1234 LDD #$1234 5: 4006 CD 5678 LDY #$5678 6: 4009 3B PSHD 7: 400A 35 PSHY 8: 400B 30 PULX 9: 400C 31 PULY 10: 400D 3F SWI What values end up in X and Y?

6. Subroutine and Stacks The System Stack Subroutines A Data Stack

7. 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS

8. 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS Stack 4006 D 1234

9. Stack 4010 4006 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 68AC

10. Stack 4010 4006 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 79BD

11. Stack 4006 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 79BD

12. Stack 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 79BD

13. Stack 4009 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 79BD

14. Stack 4009 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 8ACE

15. Stack 1: ; Subroutine example 2: 3: 4: =00004000 ORG $4000 5: 4000 EX2 6: 4000 CC 1234 LDD #$1234 7: 4003 16 400A JSR SUB1 8: 4006 16 4011 JSR SUB2 9: 4009 3F SWI 10: 11: 400A SUB1 12: 400A C3 5678 ADDD #$5678 13: 400D 16 4011 JSR SUB2 14: 4010 3D RTS 15: 16: 4011 SUB2 17: 4011 C3 1111 ADDD #$1111 18: 4014 3D RTS D 8ACE

16. Saving and restoring registers in a subroutine ;subroutine example subname pshb;save B pshx;save X ---- ----;instructions that ----;change B and X ---- pulx;restore X pulb;restore B rts Note that you MUST pull ALL registers that you pushed on the stack

17. Subroutine and Stacks The System Stack Subroutines A Data Stack

18. Using X as a stack pointer for a data stack LDY 2,X+ will pop $1234 into Y

19. Subroutine to add two numbers on the data stack

20. Subroutine to subtract two numbers on the data stack