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Topic 3 : Controlling the Computer

Topic 3 : Controlling the Computer. Machine Language/Machine Code Reference : G & L pp 159-169. A Quick Reminder of Microcode. Micromemory. Microinstruction. address. 0 + 0->MDR; MPC + 1 -> MPC;. 0. MPC + TESTZERO(A) -> MPC. 1.

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Topic 3 : Controlling the Computer

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  1. Topic 3 : Controlling the Computer Machine Language/Machine Code Reference : G & L pp 159-169

  2. A Quick Reminder of Microcode Micromemory Microinstruction address 0 + 0->MDR; MPC + 1 -> MPC; 0 MPC + TESTZERO(A) -> MPC 1 2 5 -> MPC C + MDR -> MDR; MPC + 1 -> MPC; 3 A - 1 -> A; 0 + 1 -> MPC 4 0 + 1 -> MAR; write; MPC + 1 -> MPC 5

  3. The Microprogram in Full Microinstruction 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 1 1 1 0 1 1 1 1 1 1 2 Micromemory address 1 1 1 1 1 3 1 1 1 1 1 4 1 1 1 1 1 5

  4. Evaluation of Microinstructions • Writing programs in microcode is very difficult: • cf code required to multiply two numbers • each instruction performs only a very small task. • instructions are closely tied to machine architecture. • instructions must be coded in binary.

  5. Providing More Support • If we are going to write big programs we need to provide programmers with easier to use and more powerful instructions. • Simplest languages which offer such support are called machine languages. • still at a very low level but much easier to use than microcode. • they introduce limited abstractions over the machine’s hardware, e.g. the accumulator.

  6. Overview of a Simple Machine Language • Simple language involving only 11 instructions. • Main abstraction is the accumulator which stores operands and results of arithmetic operations. • Why? - Because arithmetic operations often use the result of a preceding operation as an operand.

  7. Operations 1 & 2 • Load • moves values from memory to the accumulator. • LOAD 123 • Store • moves values from the accumulator into memory. • STORE 123

  8. Example: LOAD 103 100 ABC LOAD 103 101 DEF 102 GHI Accumulator 103 JKL 104 MNO 105 PQR STU 106 VWX 107

  9. Example: LOAD 103 100 ABC LOAD 103 101 DEF 102 GHI Accumulator 103 JKL 104 JKL MNO 105 PQR STU 106 VWX 107

  10. Example: STORE 103 100 ABC STORE 103 101 DEF 102 GHI Accumulator 103 JKL 104 AAA MNO 105 PQR STU 106 VWX 107

  11. Example: STORE 103 100 ABC STORE 103 101 DEF 102 GHI Accumulator 103 AAA 104 AAA MNO 105 PQR STU 106 VWX 107

  12. Operations 3,4,5 & 6 • Add • Adds the value from memory to the accumulator. • ADD 123 • Subtract • Subtracts the value from memory from the accumulator. • SUBTRACT 123 • Multiply • MULTIPLY 123 • Divide • DIVIDE 123

  13. The Machine Language So Far Operation Explanation LOAD M -> ACC STORE ACC -> M ADD ACC + M -> ACC SUBTRACT ACC - M -> ACC MULTIPLY ACC * M -> ACCDIVIDE ACC / M -> ACC

  14. Control Transfer (Ops 7,8 & 9) • Unconditional transfer of control. • JUMP M : Start executing instruction at memory cell M. • Conditional transfer of control • JUMPZERO M : Start executing instruction at memory cell M if the accumulator contains zero. • JUMPMSB M : Start executing instruction at memory cell M if the msb of the accumulator = 1.

  15. The Machine Language So Far Operation Explanation LOAD M -> ACC STORE ACC -> M ADD ACC + M -> ACC SUBTRACT ACC - M -> ACC MULTIPLY ACC * M -> ACCDIVIDE ACC / M -> ACC JUMP Jump to cell M JUMPZERO Jump if ACC = 0 JUMPMSB Jump if msb = 1

  16. Op Codes and Operands • We need to identify each instruction by giving it an op-code. • We use 4 bits because we have 11 instructions. • We also need to store the address of the operand. 0001000 000 000001 Operand Op-code

  17. The Machine Language So Far opcode adss Operation Explanation 0001 0010 0011 0100 0101 0110 0111 1000 1001 LOAD M -> ACC STORE ACC -> M ADD ACC + M -> ACC SUBTRACT ACC - M -> ACC MULTIPLY ACC * M -> ACCDIVIDE ACC / M -> ACC JUMP Jump to cell M JUMPZERO Jump if ACC = 0 JUMPMSB Jump if msb = 1

  18. An Example Address Op Code Operand Addr Instruction • Calculates x*x where x is initially in location 5. • Compare this with its microcode program. 1 1005 1 5 2 5005 5 5 3 2005 2 5 4 FFFF 5 000A

  19. An Example ACC : 0 Address Instruction • Calculates x*x where x is initially in location 5. • Compare this with its microcode program. 1 1005 2 5005 3 2005 4 FFFF 5 000A

  20. An Example ACC : A Address Instruction • Calculates x*x where x is initially in location 5. • Compare this with its microcode program. 1 1005 LOAD 5 -> ACC 2 5005 3 2005 4 FFFF 5 000A

  21. An Example ACC : 64 Address Instruction • Calculates x*x where x is initially in location 5. • Compare this with its microcode program. 1 1005 Contents 5 -> ACC 2 5005 ACC * Contents 5 -> ACC 3 2005 4 FFFF 5 000A

  22. An Example ACC : 64 Address Instruction • Calculates x*x where x is initially in location 5. • Compare this with its microcode program. 1 1005 Contents 5 -> ACC 2 5005 ACC * Contents 5 -> ACC 3 2005 Contents of Acc -> 5 4 FFFF 5 0064

  23. An Example ACC : 64 Address Instruction • Calculates x*x where x is initially in location 5. • Compare this with its microcode program. 1 1005 Contents 5 -> ACC 2 5005 ACC * Contents 5 -> ACC 3 2005 Contents of Acc -> 5 4 FFFF Stop 5 0064

  24. A Further Example Address Instruction 1 100D 2 200C 3 100B 4 800E 5 400D 6 200B 7 100C 8 300C 9 200C 10 7003 11 1 12 0 13 1

  25. A Further Example ACC : 1 Address Instruction 1 100D Contents 13 -> ACC 2 200C 3 100B 4 800E 5 400D 6 200B 7 100C 8 300C 9 200C 10 7003 11 1 12 0 13 1

  26. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B 4 800E 5 400D 6 200B 7 100C 8 300C 9 200C 10 7003 11 1 12 1 13 1

  27. A Further Example ACC : 1 Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E 5 400D 6 200B 7 100C 8 300C 9 200C 10 7003 11 1 12 1 13 1

  28. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D 6 200B 7 100C 8 300C 9 200C 10 7003 11 1 12 1 13 1

  29. A Further Example ACC : 0 Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B 7 100C 8 300C 9 200C 10 7003 11 1 12 1 13 1

  30. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C 8 300C 9 200C 10 7003 11 0 12 1 13 1

  31. A Further Example ACC : 1 Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C 9 200C 10 7003 11 0 12 1 13 1

  32. A Further Example ACC : 2 Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C ACC + Contents 12 -> ACC 9 200C 10 7003 11 0 12 1 13 1

  33. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C ACC + Contents 12 -> ACC 9 200C ACC -> 12 10 7003 11 0 12 2 13 1

  34. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C ACC + Contents 12 -> ACC 9 200C ACC -> 12 10 7003 Jump 3 11 0 12 2 13 1

  35. A Further Example ACC : 0 Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C ACC + Contents 12 -> ACC 9 200C ACC -> 12 10 7003 Jump 3 11 0 12 2 13 1

  36. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C ACC + Contents 12 -> ACC 9 200C ACC -> 12 10 7003 Jump 3 11 0 12 2 13 1

  37. A Further Example Address Instruction 1 100D Contents 13 -> ACC 2 200C ACC -> 12 3 100B Contents 11 -> ACC 4 800E Jump to 14 if ACC 0 5 400D ACC - Contents 13 -> ACC 6 200B Store ACC -> 11 7 100C Contents 12 -> ACC 8 300C ACC + Contents 12 -> ACC 9 200C ACC -> 12 10 7003 Jump 3 11 0 -- holds x initially 12 2 -- ends up with y where y=2^x 13 1 -- holds value 1

  38. The Machine Language So Far opcode adss Operation Explanation 0001 0010 0011 0100 0101 0110 0111 1000 1001 LOAD M -> ACC STORE ACC -> M ADD ACC + M -> ACC SUBTRACT ACC - M -> ACC MULTIPLY ACC * M -> ACCDIVIDE ACC / M -> ACC JUMP Jump to cell M JUMPZERO Jump if ACC = 0 JUMPMSB Jump if msb = 1

  39. Modular Structure (Operations 10 & 11) • Two instructions not yet described, i.e. JUMPSUB and RETURN • These instructions may be used to structure programs, i.e. subroutines. • Equivalent to gosubs (BASIC) or function calls.

  40. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  41. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  42. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  43. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  44. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  45. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  46. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  47. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  48. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  49. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

  50. Modular Structure ... contd. instruction 1 instruction 2 instruction 3 JUMPSUB M instruction 5 instruction 6 JUMPSUB M instruction 8 instruction 9 M: does something does something else and something else RETURN M

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