Binghamton University. CS-140 Fall Pippin

Transcription

1 Pippin 1

2 Pippin Rick Decker and Stuart Hirshfield The Analytical Engine: An Introdution to Computer Science Using the Internet [1998] Imaginary Computer with a very simple architecture The final project is to simulate a Pippin computer 2

3 The Pippin Architecture CPU Supports simple arithmetic (+,-,*,/), Supports simple logic (AND, and NOT) Can fetch/store single integers from memory All results fed into a single integer register called : ACCUMULATOR Supports simple (unconditional) branching Supports conditional branching based on ACCUMULATOR value Keeps track of location of next instruction in : instructionpointer 3

4 The Pippin Architecture - Memory Data Memory consists of a list of 2048 integers (=8K bytes) Addresses are indexes into this list There is a memorybase register added to the index Code Memory consists of a list of 1024 instructions (=4K bytes) The instructionpointer register indexes into this list 4

5 Pippin Assembly Language Assembly language consists of: OpCode (4 bits) What does this instruction do? Mode (? bits) How do I treat the argument? Argument Numeric value 5

6 Pippin Op-Codes Mnemonic Num Meaning NOP 0x0 No operation LOD 0x1 Load data from argument into Accumulator STO 0x2 Store data from Accumulator into data Memory ADD 0x3 Add argument to Accumulator SUB 0x4 Subtract argument from Accumulator MUL 0x5 Multiply Accumulator by argument DIV 0x6 Divide Accumulator by argument (Integer division) AND 0x7 Logical AND Accumulator with argument NOT 0x8 Invert accumulator True/False Value (0/1) CMPL 0x9 Set Accumulator to 1 if argument<0, else set Accumulator to 0 CMPZ 0xa Set Accumulator to 1 if argument==0, else set Accumulator to 0 JUMP 0xb Set instructionpointer to argument JMPZ 0xc Set instructionpointer to argument if Accumulator is zero HALT 0xf Stop execution No argument op-codes No immediate args 6

7 Pippin Assembler Arguments Arguments may be in one of four different argument modes null No argument specified (required for no argument opcodes) IMMEDIATE Argument specified in the instruction itself DIRECT Instruction contains index (offset from memorybase) of data in memory INDIRECT Instruction contains index (offset from memory base) of an index (offset from memorybase) of data in memory 7

8 Pippin Instruction Cycle Fetch Instruction Execute Instruction Fetch instruction at instructionpointer Instructions increment instructionpointer JUMP and JMPZ may modify instructionpointer HALT stops the loop 8

9 Example Pippin ASM Program Direct Mode LOD 0 // accum=argument stored in memory location 0 DIV #2 MUL #2 SUB 0 // accum=accum/2 (rounds down) // if arg is even, accum= arg, else arg-1 // Subtract arg from accum STO 1 // Store 0 or -1 at location 1 CMPZ 1 HALT // Sets accum to 1 if even, 0 if odd Immediate Indirect Mode 9

10 TimeSharing in Pippin Divide both instruction and data memory into 4 equal parts Each part is devoted to a different job (program invocation) CPU devotes timeslice cycles to a job Then, saves the state of that job Accumulator, instructionpointer, memorybase, etc. Then restores the state of the next job Accumulator, instructionpointer, memorybase, etc. Then devotes timeslice cycles to the next job 10