Descriptions for ALU Operations

Describe oprtations

Write each operation.
The calculation result has 9-bit bus so that we can easily generate the carry flag.
After that, carry flag and operation result are reassigned to each variable.

Notes;

Followint operators are not used, multiply "*", divide "/", right shift ">>" and left "<<" because these operator make large circuits.
In this exercise, one bit shift operations are writen by bit manupiration.
Signal tmp has carry signal.
Separatoer // is followed by comment.

  ...
  reg    [8:0] tmp;		// operation result

  always @( ... or ... or ... )
  begin
    case ( CB )
    `IADD   : tmp <= { 1'b0, A } + { 1'b0, B }; // addition
       ...
       ...
       ...
    `ISWP   : tmp <= { 1'b0, A[3:0], A[7:4] }; // nibble swap
    default : tmp <= 9'bxxxxxxxxx;	       // don't care (for simulation)
    endcase
  end
  ...
  ...
  assign Y    = ... ;		// reassignment of result
  ...

Next, describe flags .

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