Cse675.02.F.ALUDesign_part2

# Cse675.02.F.ALUDesign_part2 - Set Less Than(slt Function...

This preview shows pages 1–4. Sign up to view the full content.

1 g. babic Presentation F 14 slt function is defined as: 000 … 001 if A < B, i.e. if A – B < 0 A slt B = 000 … 000 if A ± B, i.e. if A – B ± 0 Thus, each 1-bit ALU should have an additional input (called Less ”), that will provide results for slt function. This input has value 0 for all but 1-bit ALU for the least significant bit. For the least significant bit Less value should be sign of A – B Set Less Than (slt) Function 0 3 R e s u l t O p e r a t i o n a 1 C a r r y I n C a r r y O u t 0 1 B i n v e r t b 2 L e s s 32-bit ALU With 5 Functions 1-bit ALU1-ALU30 Carry Out S e t a 3 1 0 A L U 0 R e s u l t 0 a 0 R e s u l t 1 a 1 0 R e s u l t 2 a 2 0 O p e r a t i o n b 3 1 b 0 b 1 b 2 R e s u l t 3 1 O v e r f l o w B i n v e r t C a r r y I n L e s s C a r r y I n C a r r y O u t A L U 1 L e s s C a r r y I n C a r r y O u t A L U 2 L e s s C a r r y I n C a r r y O u t A L U 3 1 L e s s C a r r y I n slt function: Operation = 3 1-bit ALU31 the most significant bit 0 3 R e s u l t O p e r a t i o n a 1 C a r r y I n 0 1 B i n v e r t b 2 L e s s S e t O v e r f l o w d e t e c t i o n O v e r f l o w Carry Out + =0 Binvert =1

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 g. babic Presentation F 32-bit ALU with 5 Functions and Zero Function Binvert (1 line) Operation (2 lines) and 0 00 or 0 01 add 0 10 subtract 1 10 slt 1 11 Control lines Carry Out Binvert 17 32-bit ALU with 6 Functions A nor B = A and B Figure B.5.10 (Top) Carry Out Function Ainvert Binvert Operation and 0 0 00 or 0 0 01 add 0 0 10 subtract 0 1 10 slt 0 1 11 nor 1 1 00 Figure B.5.12 + Carry Out + Binvert Binvert
3 g. babic Presentation F 18 We have (so far) designed an ALU for most (integer) arithmetic and logic functions required by the core MIPS ISA 32-bit ALU with 6 functions omits support for: – shift instructions – XOR logic instruction – integer multiply and divide instructions. Shift instructions: – It would be possible to widen 1-bit ALU multiplexer to include 1-bit shift left and/or 1-bit shift right. – Hardware designers created the circuit called a barrel shifter, which can shift from 1 to 31 bits in less time than it takes to add two 32-bit numbers. Thus, shifting is normally done outside the ALU. Integer multiply/divide is also usually done outside the ALU.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 11

Cse675.02.F.ALUDesign_part2 - Set Less Than(slt Function...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online