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encoding-scheme.md

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Encoding Scheme

ENCODING SCHEME

The proposed encoding scheme for the circuit would be:

  • 31-28: OPCODE
  • 27-24: RY
  • 23-20: RA
  • 19-16: RB
  • 15-00: Immediate

DECODER

INSTRUCTION SET

The instuction set needed to define for the processor are

  • MOV RA RB: Content of RB is transferred to RA
  • MVI RA Im: The Immediate value Im is stored in RA
  • LOAD RA RB X : The content of the memory location [[RB]+X] is loaded into RA, where X is a 16bit unsigned immediate value
  • STORE RA RB X: The content of register RA is stored in memory location [[RB]+X] where X is again, a 16bit unsigned immediate value
  • ADD RA RB RC: RA = RB + RC
  • ADI RA RB Im: RA = RB + Im, where Im is a 32-bit unsigned extended immediate value
  • SUB RA RB RC: RA = RB - RC
  • SUI RA RB Im: RA = RB - Im, where Im is a 32-bit unsigned extended immediate value
  • AND RA RB RC: RA = RB AND RC
  • ANI RA RB IM: RA = RB AND Im, where Im is a 32-bit unsigned extended immediate value
  • OR RA RB RC: RA = RB OR RC
  • ORI RA RB IM: RA = RB OR Im, where Im is a 32-bit unsigned extended immediate value
  • HLT: Stops the Execution at current address

INSTRUCTION ENCODING

The OPCODES FOR THE OPERATIONS ARE WITH ALU MAPPING :

  • ADD: 0000 (0) (SUM)
  • ADI: 0001 (1) (SUM)
  • SUB: 0010 (2) (DIFF)
  • SUI: 0011 (3) (DIFF)
  • AND: 0100 (4) (AND)
  • ANI: 0101 (5) (AND)
  • OR: 0110 (6) (OR)
  • ORI: 0111 (7) (OR)
  • MOV: 1000 (8) (RA)
  • MVI: 1001 (9) (RB)
  • LOAD: 1010 (10) (SUM)
  • STORE: 1011 (11) (SUM)
  • HLT: 1111 (15) (NOP)

REGISTER ENCODING

There are 8 registers available, those are:

  • R1: 000
  • R2: 001
  • R3: 010
  • R4: 011
  • R5: 100
  • R6: 101
  • R7: 110
  • R8: 111

NOTE: The immediate values are 16-bit

NOTE: The entirety of OPCODE is ALU_SELECT

LITERAL ENCODING

  • All literals are expected to be in hexadecimal, if not found, they are converted into hex.
  • All immediate values would be capped at 16 bit

INSTRUCTION EXAMPLE

For example the instruction

ADI R2 R1 56

would translate to:

0010 0001 0000 0000 0000000000111000

0010 0001 0000 0000 0000 0000 0011 1000

And converting into hex, we have

21000038