Description

 

In this project, you are required to extend the MIPS single-cycle implementation by implementing additional instructions. You will use ModelSim simulator [1] to develop and test your code. You are required to implement your assigned 6 instructions (selected from following 20 instructions). Note that your set of 6 instructions will be emailed to you or your group member.

R-format (6): brn, brz, balrz, sll, sllv, srlv

I-format (11): xori , andi, nori, bgez, bgezal, bgtz, bltz,  jm, jalm, jsp, jspal

J-format (3): bz, balz, jal

You must design the revised single-cycle datapath and revised control units which make a processor that executes your instructions as well as the instructions implemented already in the design. After designing the new enhanced processor, you will implement it in Verilog HDL.

Specifications of New Instructions

Instr     Type    Code               Syntax                        Meaning

1. bltz I-type  opcode=1         bltz     $rs, Target            if R[rs] < 0, branches to PC-relative address

(formed as beq & bne do)

2. bgtz I-type opcode=38       bgtz     $rs, Target       if  R[rs] > 0, branch to PC-relative address (formed

as beq & bne do)

3. bgez I-type opcode=39      bgez     $rs, Target                  if  R[rs] >= 0, branch to PC-relative address

(formed as beq & bne do)

4. bgezal I-type opcode=35   bgezal $rs, Target         if  R[rs] >= 0, branch to PC-relative address (formed

as beq & bne do), link address is stored in register 31.

5. xori I-type opcode=14       xori    $rt, $rs, imm16   Put the logical XOR of register $rs and the zero      extended immediate into register $rt.
6. nori I-type opcode=13       nori    $rt, $rs, imm16   Put the logical NOR of register $rs and the zero                                                                                     extended immediate into register $rt.
7. andi I-type opcode=12       andi    $rt, $rs, imm16   Put the logical AND of register $rs and the zero                                                                                      extended immediate into register $rt.
8. brz R-type funct=20          brz $rs                 if  Status [Z] = 1, branches to address found in                                                                                                    register $rs.
9. brn R-type funct=21          brn $rs     if  Status [N] = 1, branches to address found in                                                                                                    register $rs.
10. balrz R-type funct=22 balrz $rs, $rd     if  Status [Z] = 1, branches to address found in register

$rs link address is stored in $rd (which defaults to 31)

11. bz J-type opcode=24       bz Target             if Status [Z] = 1, branches to pseudo-direct address

(formed as j does)

12. balz J-type opcode=26       balz Target          if Status [Z] = 1, branches to pseudo-direct address

(formed as jal does), link address is stored in register 31

13. jal J-type opcode=3         jal Target             jump to pseudo-direct address (formed as j does),

link address is stored in register 31

14. jm I-type opcode=16        jm imm16($rs)                jumps to address found in memory (indirect jump)
15. jalm I-type opcode=17        jalm $rt, imm16($rs)   jumps to address found in memory (indirect jump),                         link addressis stored in $rt (which defaults to 31)
16. jsp I-type opcode=18        jsp                                jumps to address found in memory where the memory                                                                                                  address is written in register 29 ($sp).
17. jspal I-type opcode=19        jspal                             jumps to address found in memory where the memory

address is written in register 29 ($sp) and link address is stored in memory (DataMemory[Register[29]]).

18. sll R-type func=0             sll $rd, $rt, shamt         shift register $rt to left by shift amount (shamt) and store the result in register $rd.
19. sllv R-type func=4             sllv $rd, $rt, $rs           shift register $rt to left by the value in register $rs, and  store the result in register $rd.
20. srlv R-type func=6             srlv $rd, $rt, $rs          shift register $rt to right by the value in register $rs, and store the result in register $rd.

Status Register

Some of the conditional branches test the Z and N bits in the Status register. So the MIPS datapath will need to have a Status register, with the following 2 bits: Z (if the ALU result is zero) and N (if the ALU result is negative). The Status register will be loaded with the ALU results each clock cycle.