Bottom-Up-ALU

A 32-Bit Bottom Up ALU made using Ripple Carry Adder, Binary Multiplier(built using Full Adders) and other basic logical operations.

ALU Opcode Operations

The ALU performs different operations based on the provided opcode. Below is a table that describes the ALU's operations:

Opcode	Operation	Description
000	Addition (+)	Performs the addition of A and B.
001	Subtraction (-)	Performs the subtraction (A - B). Overflow is checked for signed numbers.
010	Multiplication (*)	Performs multiplication of A and B using a full adder-based multiplier.
011	Division (/)	Performs division (A / B) and returns both quotient and remainder. Handles division by zero.
100	Right Shift (>>)	Performs arithmetic right shift on A by the number of positions specified in the lower 5 bits of B.
101	Left Shift (<<)	Performs logical left shift on A by the number of positions specified in the lower 5 bits of B.
110	Bitwise AND (&)	Performs bitwise AND operation between A and B.
111	Bitwise OR	Performs bitwise OR operation between A and B.

Notes:

• Overflow (ov): For addition and subtraction, overflow is checked for signed operations, with overflow occurring when the sign bits do not match.
• Division: When B is zero, both the quotient and remainder are set to zero.
• Shift Operations: Both shift operations handle up to 32 positions (A is shifted by B[4:0]), ensuring that the number of shift positions is valid for 32-bit values.

Working of the multiplier

• Using the generate block, we iterate over each bit (from 0 to 31). If the bit b[i] is 1, a partial product is generated by shifting a left by i positions. If b[i] is 0, the partial product is set to zero. This is assigned to partial_products[i].

• An instance of an RCA adder is used to add the lower 32 bits of the running sum (temp_sum[i][31:0]) and the current partial product (partial_products[i][31:0]). The sum is stored in sum[i], and the carry out is stored in carry_out[i].

• The sum of the lower 32 bits of the running total is assigned to the lower 32 bits of temp_sum[i+1]. The upper 32 bits of the running total are updated by adding the upper 32 bits of the current partial product and the carry-out, adjusted by shifting the carry-out to the appropriate position. The final product is assigned to prod.