The description of the flag

The flag output is a 4-bit bus and there are sign-flag "S", zero flag "Z", overflow flag "V", carry-flag "C" in it. The order of the bit at the bus is free. The change of the flag depends on each direction and is as follows.

Arithmetic operation

Operation	S	Z	V	C
Addition (ADD)	'1' when result is minus.	'1' when result is zero.	'1' when result is incorrect in signed addition.	'1' when carry occurs in unsigned addition.
Decrement (DEC)	'1' when result is minus.	'1' when result is zero.	'1' when result is incorrect in signed addition.	'1' when carry occurs in unsigned addition.
Inclement (INC)	'1' when result is minus.	'1' when result is zero.	'1' when result is incorrect in signed subtranction.	'1' when borrow occurs in unsigned subtraction.
The subtraction (SUB)	'1' when result is minus.	'1' when result is zero.	'1' when result is incorrect in signed addition.	'1' when borrow occurs in unsigned subtraction.

Logical operation

Operation	S	Z	V	C
Boolean ADD (OR)	Same as most significant bit.	'1' when result is zero.	always 0.	always 0.
The exclusive OR (The XOR)	Same as most significant bit.	'1' when result is zero.	always 0.	always 0.
AND (AND)	Same as most significant bit.	'1' when result is zero.	always 0.	always 0.
The logical NOT (NOT)	Same as most significant bit.	'1' when result is zero.	always 0.	always 0.

The shift type direction

The calculation kind	S	Z	V	C
The arithmetic right shift (ASR)	Same as most significant bit.	'1' when result is zero.	It is always 0.	Same as least significant bit.
The arithmetic left shift (ASL)	Same as most significant bit.	'1' when result is zero.	'1' when bit 15 and bit 14 of operand are different value.	Same as most significant bit.
The logic right shift (LSR)	Same as most significant bit.	'1' when result is zero.	It is always 0.	Same as least significant bit.
The logic left shift (LSL)	Same as most significant bit.	'1' when result is zero.	It is always 0.	Same as most significant bit.
The dextroversion (ROR)	Same as most significant bit.	'1' when result is zero.	It is always 0.	Same as least significant bit.
The anticlockwise-rotation (ROL)	Same as most significant bit.	'1' when result is zero.	It is always 0.	Same as most significant bit.
The byte swap (SWP)	Same as most significant bit.	'1' when result is zero.	It is always 0.	It is always 0.

The special operational function

The calculation kind	S	Z	V	C
The path (PAS)	X	X	X	X	Don't care because it isn't stored in FR.

Each flag can be generated as follows;

• Sign flag : Same as the most significant bit of the result.
• Zero flag : It becomes 1 when the result is zero.
• Carry flag : It becomes 1 when carry occurrs in addition, borrow occurrs in subtraction, or same as flowed bit in shift and rotate operations.
• Overflow flag : '1' when the result is incorrect in signed operations;
  1. In ADD operation, set '1' when sign of augend and sign of addend are same value, and sign of augend and sign of addend are different value.
     
     
  2. In SUB operation, set '1' when sign of minuend and sign of subtrahend are different value, and sign of minuend and sign of result are different value .
     
     
  3. In INC operation, set '1' when the augend is a positive number and the result is a negative number.
     
     
  4. In DEC operation, set '1' when the minuend is a negative number and the result is a positive number.
     
     
  5. IN ASL operation, set '1' when bit 15 and bit 14 of operand are different value.

  reg V ;                                  // for Overflow
  
  always @ (A or B or tmp or CB)
    case (CB)
    `IADD   : V <= ( ( Condition ) && (  Condition ) ) ? 1 : 0;
    `ISUB   : V <= ( ( Condition ) && (  Condition ) ) ? 1 : 0;
    `IINC   : V <= ( ( Condition ) && (  Condition ) ) ? 1 : 0;
    `IDEC   : V <= ( ( Condition ) && (  Condition ) ) ? 1 : 0;
    `IASL   : V <= ( A[15] != tmp[15] ) ? 1 : 0;
    default : V <= 0;
    endcase
  ...
  assign F[3] = ...... ;	// Sign flag
  assign F[2] = ...... ;	// Zero flag
  assign F[1] = V;		// Overflow flag
  assign F[0] = ...... ;	// Carry flag
  ...

Next, functional simulation simulation of the KITE ALU.