CS 232: Project 5

Project 5: Programmable Lights II

Due Monday 25 October 2021

Purpose: The purpose of this project is to build a more sophisticated programmable light display. The machine language for this project includes both a conditional and an unconditional branch, enabling you to implement loops in your program.

Programmable Circuit Design

The new programmable light display will be a state machine with three states that can execute four types of instructions. Each instruction will be 10 bits long. The state machine has two data registers, the light register [LR] and the accumulator [ACC], both of which hold 8-bits. The instruction set is given below.

Opcode	Format	Description
00	[C1 C0] [Dest1 Dest0] [Src1 Src0] [Val3 Val2 Val1 Val0]	Move from SRC to DEST
	Dest10: 00 = ACC, 01 = LR, 10 = ACC low 4 bits, 11 = ACC high 4 bits
	Src10: 00 = ACC, 01 = LR, 10 = IR low 4 bits sign extended, 11 = all 1s
01	[C1 C0] [Op2 Op1 Op0] [Src1 Src0] [Dest0] [Val1 Val0]	Binary operator DEST = DEST op SRC
	Op210: 000 = add, 001 = sub, 010 = shift left, 011 = shift right maintain sign bit
	Op210: 100 = xor, 101 = and, 110 = rotate left, 111 = rotate right
	Src10: 00 = ACC, 01 = LR, 10 = IR low 2 bits sign extended, 11 = all 1s
	Dest0: 0 = ACC, 1 = LR
10	[C1 C0] [U3 U2 U1 U0] [Addr3 Addr2 Addr1 Addr0]	Branch to ADDR
11	[C1 C0] [Src0] [U2 U1 U0] [Addr3 Addr2 Addr1 Addr0]	Branch to ADDR if SRC is 0
	Src0: 0 = ACC, 1 = LR

There are four types of instructions: MOVE (00), BINARY (01), BRANCH (10), CONDITIONAL BRANCH (11). Move instructions copy data from the source location to the destination. Binary instructions execute some type of binary operation on the destination and source and store the result in the destination (note that shift/rotate are just really unary operations that shift/rotate the source by 1 bit). Branch instructions uncondtionally branch to the address given in the instruction. Conditional branch instructions go to the address in the instruction only if the source register is equal to zero.

Tasks

Setup
Start by creating a folder for the project (and if you are using Quartus, a project in Quartus). There will be 3 VHDL files (and no BDF files) in the project.
- pld2.vhd: this is the file that implements the circuit shown in the lab page. It uses the pldrom as a component.
- pldrom.vhd: this is the file that holds the ROM
- pldbench.vhd: this is the testbench file that defines the inputs to pld2. You will download it.
Create a ROM to hold the program
Create a simple read-only memory [ROM] using VHDL. You can use last week's ROM as a starting point. Call it pldrom.

The pldrom should take one input signal addr that should be a 4-bit std_logic_vector. It should have one output signal data that should be a 10-bit std_logic_vector.

The content of your ROM architecture should be a single conditional signal assignment. You will use the following for your first test (it tests branching and some of the other operations). Later, you will test with an additional program and then write two of your own program. The 10-bit values stored at each address location are the program.
```
  data <= 
    "0001100000" when addr = "0000" else -- move 0s to LR   00000000/00000000
    "0001110000" when addr = "0001" else -- move 1s to LR   11111111/00000000
    "0001101010" when addr = "0010" else -- move 1010 to LR 11111010/00000000
    "0010101000" when addr = "0011" else -- move 8 to ACC   11111010/00001000
    "0101001100" when addr = "0100" else -- shift LR left   
    "0100011000" when addr = "0101" else -- add -1 to ACC  
    "1100001000" when addr = "0110" else -- branch if  zero  
    "1000000100" when addr = "0111" else -- branch  
    "0001110000" when addr = "1000" else -- set LR to 1s    11111111/00000000
    "1000000000" when addr = "1001" else -- branch to zero  11111111/00000000
    "0101010101" when addr = "1010" else -- garbage
    "1010101010" when addr = "1011" else -- garbage
    "1100110011" when addr = "1100" else -- garbage
    "0011001100" when addr = "1101" else -- garbage
    "0000000000" when addr = "1110" else -- garbage
    "1111111111";                        -- garbage	
```
Note about file organization: The code here contains the first program you will use to test your programmable light display. When you write additional programs, it will be easiest to test them if they are also in a file/entity named pldrom. I have found the easiest way to change from program to program is to keep a separate file for each, then copy-paste whichever program you want to run into pldrom.vhd, recompile, and rerun the program.
Start the main design
Make a new VHDL file. Name the entity pld2. You can use your VHDL code from the prior project as a starting point, if you wish (but you can also start over from scratch). Make the following quick modifications.
1. Update the IR, ROMvalue, and pldrom component statement to use 10 bits for the instructions.
2. The state_type will need three states: sFetch, sExecute1, and sExecute2.
3. Add two new internal signals ACC and SRC that are 8 bit UNSIGNED type.
4. Update the reset case so you are assigning 10 bits to the IR.
5. Update the sFetch case so the next state is sExecute1.
6. Delete all of the current code under state sExecute. Then set up cases for when sExecute1 and when sExecute2.
Note to board users: You should keep the slowclock process in your code, because you will run this on the board.
Define the Execute 1 actions
In state sExecute1, the move and binary operation instructions should assign the appropriate value to the SRC signal. The move instruction uses IR(5 downto 4) and the binary instruction uses IR(4 downto 3).

The two branch instructions should assign the appropriate value to the PC. In the case of the conditional branch, it should assign a new address to the PC only if the specified register (ACC or LR) is equal to 0.
Define the Execute 2 actions
In state sExecute2 the move instruction should assign the correct bits of SRC to the correct destination as specified by IR(7 downto 6). Note that if the destination is the lower or upper 4 bits of the ACC, you should use the lower 4 bits of the source.

The binary instruction should assign to either the ACC or LR--depending upon IR(2)--the result of the specified binary operation as given in IR(7 downto 5).

The two branch instructions should do nothing in execute 2.
Test the circuit
Test your system using this test bench file. Note that you may need to rename the circuit in the pldbench.vhd file to match your top level entity.

Note to board users: If you still are using a slowclock signal, assign slowclock <= clk; for the simulation. Then set it back when you run this on the board.

If you run the program listed above, you should get the output below. (Click on the image to make it bigger.)
```
ghdl -a pldbench.vhd pld2.vhd pldrom.vhd
ghdl -e pldbench
ghdl -r pldbench --vcd=pldbench.vcd
gtkwave pldbench.vcd &
```

Test the circuit again

Save your pldrom.vdh into another file, e.g. pldrom_test1.vhd so that you can use it again, if needed. Then, update pldrom.vhd's code to use this program, which tests each operator

  data <= 
    "0001110000" when addr = "0000" else -- move 11111111 to the LR    
    "0011100000" when addr = "0001" else -- move 0000 from the IR to the high 4 bits of the ACC
    "0010100010" when addr = "0010" else -- move 0010 from the IR to the low 4 bits of the ACC
    "0100000100" when addr = "0011" else -- Add ACC to LR and put it back into the LR
    "0100000100" when addr = "0100" else -- Add ACC to LR and put it back into the LR
    "0100100100" when addr = "0101" else -- Subtract ACC from LR and put it back into the LR
    "0101001100" when addr = "0110" else -- Shift the LR left and write it back to the LR
    "0101101100" when addr = "0111" else -- Shift the LR right and write it back to the LR
    "0111101100" when addr = "1000" else -- Rotate the LR right and write it back to the LR
    "0101101100" when addr = "1001" else -- Shift the LR right and write it back to the LR
    "0110011100" when addr = "1010" else -- XOR the LR with all 1s and write it back to the LR (bit inversion)
    "0110110101" when addr = "1011" else -- AND the LR with 01 (sign-extended)
    "0100010110" when addr = "1100" else -- ADD the LR with 10 (sign-extended)
    "1111111111";                        -- garbage

If you run the program listed above, you should get the output below. (Click on the image to make it bigger.)

ghdl -a pldbench.vhd pld2.vhd pldrom.vhd
ghdl -e pldbench
ghdl -r pldbench --vcd=pldbench.vcd
gtkwave pldbench.vcd &

Write a specific program
Write a program that loads 16 into the light register and has it count down to 0. Then it should flash between all 1s and all 0s 8 times and repeat from the beginning.
Write one more program
Write one more program. It must include at least one branch instruction. In your report (instructions below), describe your goals for the program (what should it do?) and how it does it. Be sure to identify the branching.
Demonstrate both programs
For each of the two programs, make a movie demonstrating it in action. If you are using the board, program the board and take a movie. If you are not using the board, run vcd_movie.py and record it.

Extensions

Make longer programs (make the ROM bigger).
Write more programs.
Write a simple assembler (in python, for example) that converts instructions from a simple, human readable language, into the set of machine instructions for your pldrom.
If you are using the board, add a hold/freeze button to the display.
If you are using the board, add one or more switches/buttons that let you speed up or slow down the clock.
Add instructions to the instruction set. You can add variations on the branch instuctions without adding more bits to the instruction length by making use of their unused bits. For example, you could add branch conditions like > 0, < 0 or make comparisons between the values in the two registers.
Be creative.

Report

Create a wiki page with your report. For each task, write a short description of the task, in your own words.

Include a description of your top-level design.
Include a description of the two programs you wrote. The report can contain either a detailed explanation or you can put a detailed explanation in your VHDL code and a qualitative explanation in the report.
Include a waveform simulation (gtkwave output) and a video of the required program.
Include either both a waveform simulation and a video of your additional creative program.
Describe any other testing you undertook to prove the circuit works.
Include a description, and pictures, of any extensions.

Handin

Give your wiki page the label cs232f21project5.

Put your VHDL files in a folder called project5 in your private subdirectory on the courses server. Be sure your code is properly commented, including having your name at the top of each code file.