Description
1 Objective
The objective of this lab is to design a MIPSdatapath for R-type instructions (specified in
Table 1) as illustrated in Figures 1 to 6.
2 Required Knowledge
• How to write VHDL code using the behavioral and structural models.
clock
Reset
Figure 1: Top-level block diagram of Datapath
Dout Dout
Figure 2:Programcounter register (PC) Figure3:Programcounteradder(PCADD)
Dout
Datapath
32
clock
Reset
Din
32
32 PC PCADD
32
32
Lab 4-CECS 341 Summer 2021
Dout Dout
Din Din
Figure4:Control Figure 5: ALUcontrol
• How to use packages inVHDL.
• How to use the Xilinx Vivado Design Suite to write VHDL code, create block
designs, add VHDL modules to block designs and create test benches.
3 Design
The objective of this lab is to design the MIPS datapath (and control unit) to implement the
R-type instructions listed in Table 1. To accomplish this, the following components must
first be designed using behavioralVHDL:
• The Program Counter (PC) (Figure 2)
• The Control Unit (Figure 4)
• The ALU Control Unit (Figure 5)
• The PCADD (Figure 3)
In addition, a working design for the ALU, Register-File and Instruction Memory are
provided on the Beachboard. You will have to modify the provided ALU to add the
functionality for the slt instruction. The provided Register-File and Instruction memory
units must be used as they are pre-loaded with initial values and the test program,
respectively.
The datapath should be designed as a block design. Figure 6 illustrates the
connections between the components. Table 2 includes all the components that must be
designed, as well as the datapath, and the method by which the design is to be
implemented.
Control
1
6
ALU
Control
4
6
Lab 4-CECS 341 Summer 2021
Figure6:DatapathforR-typeinstructions
Table1:R-type instructions toimplement
*For splitting a bus into smaller width buses, use the Slice IP.
*Use the specified names for both file and input and output ports in case of datapath.
4 Testing
The registers in the register file are initialized to values shown in Table 3. The instruction
memory contains the test program which is shown in below. Calculate the final values of
the registers after the completion of the execution of the test program and complete Table
3.
No Operation Mnemonic Opcodehex Functionhex
1 Add add 00 20
2 Add unsigned addu 00 21
3 Subract sub 00 22
4 Subract unsigned subu 00 23
5 And and 00 24
6 Or or 00 25
7 Xor xor 00 26
8 Nor nor 00 27
9 Set less than slt 00 2A
10 Set less than unsigned sltu 00 2B
Lab 4-CECS 341 Summer 2021
Table 2: Components to design
No Component VHDL model Design
model
1 PC Behavioral HDL
2 PCADD Behavioral HDL
3 Control Unit Behavioral HDL
4 ALU Control Unit Behavioral HDL
5 Datapath – Block Design
Build a testbench with a clock period of 20ns and run the simulation for 1 clock cycles with
reset=’1’ and for 10 clock cycles with reset=’0’. Compare the final values of the registers
from the simulation with the values you calculated in Table 3.
The test program in instruction memory
add $t0, $t1, $t2
addu$t1,$t2,$t3
and $t2, $t3, $t4
nor $t3, $t4, $t5
or $t4, $t5, $t6
xor $t5, $t6, $t7
sub $s0, $s1, $s2
subu $s1, $s2, $s3
slt $s2, $s3, $s4
sltu$s3,$s4,$s5
Table 3. Initial values of registers
No Register Calculated Simulated
Initial valuehex Final valuehex Initial valuehex Final valuehex
0 $zero 00000000 00000000
1 $at 00000000 00000000
2 $v0 00000000 00000000
3 $v1 00000000 00000000
Lab 4-CECS 341 Summer 2021
4 $a0 00000000 00000000
5 $a1 00000000 00000000
6 $a2 00000000 00000000
7 $a3 00000000 00000000
8 $t0 00000009 00000009
9 $t1 0000000A 0000000A
10 $t2 0000000B 0000000B
11 $t3 0000000C 0000000C
12 $t4 0000000D 0000000D
13 $t5 0000000E 0000000E
14 $t6 0000000F 0000000F
15 $t7 00000010 00000010
16 $s0 00000011 00000011
17 $s1 00000012 00000012
18 $s2 00000013 00000013
19 $s3 00000014 00000014
20 $s4 00000015 00000015
21 $s5 00000016 00000016
22 $s6 00000017 00000017
23 $s7 00000018 00000018
24 $t8 00000019 00000019
25 $t9 0000001A 0000001A
Lab 4-CECS 341 Summer 2021
26 $k0 00000000 00000000
27 $k1 00000000 00000000
28 $gp 00000000 00000000
29 $sp 00000000 00000000
30 $fp 00000000 00000000
31 $ra 00000000 00000000
5 Lab Deliverables
Submit a ZIPPED file with the following syntax rtypedatapath_LastName(s).zip.
The zipped file should include the following files:
1. Lab 4 Project folder (folder containing all the files of your design including Xilinx generated
files).
2. Completed Table 3
3. A comprehensive lab report describing:
– Your method for designing the datapath components
– The new HDL codes developed for each datapath component
– Required modification on the provided ALU to add the functionality for the slt
instruction
– The testbench developed to validate your design
4. Snapshot of your datapath design
5. Final simulation waveform
Submit the zipped file through the Beachboard.
