Project 5: Programmable Lights II
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.
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.
|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 two source values and store the result in the destination. In this instruction set, the destination is also one of the source values. 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.
- Start by creating a project in Quartus. I'll refer to the project as pld2 for the top level entity.
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 can use the following for testing. Later, you will need to write 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
Make a new VHDL file. Name the entity pld2. Copy your VHDL code from
the prior project as a starting point, if you wish. Make the following
quick modifications. (Leave the slowclock process.)
- Update your IR, ROMvalue, and pldrom component statement to use 10 bits for the instructions.
- Your state_type will need three states: sFetch, sExecute1, and sExecute2.
- Add two new internal signals ACC and SRC that are 8 bit UNSIGNED type.
- Update your reset case so you are assigning 10 bits to the IR.
- Update your sFetch case so the next state is sExecute1.
- Delete all of your current code under state sExecute. Then set up cases for when sExecute1 and when sExecute2.
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
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.
In state sExecute2 the move instruction should assign the correct bits
of SRC to the correct destination as specified by IR(7 downto 6).
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.
Test your system using this test bench
file. If you still are using a slowclock signal, assign slowclock
<= clk; for the simulation. Then set it back when testing on the
board. If you run the program listed above, you should get the output
below. Note that you may need to rename the circuit in my
pldbench.vhd file to match your top level entity. (Click on the image
to make it bigger.)
ghdl -a pldbench.vhd pld.vhd pldrom.vhd ghdl -e pldbench ghdl -r pldbench --vcd=pldbench.vcd gtkwave pldbench.vcd &
- 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 two more programs. You should make use of branching in at least one of your programs. Be prepared to demonstrate your favorite at the beginning of lab.
- 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.
- Add a hold/freeze button to the display.
- Add one or more switches/buttons that let you speed up or slow down the clock.
- Be creative.
Create a wiki page with your writeup. For each task, write a short description of the task, in your own words.
- Include a description of your top-level design.
- Include the two programs you wrote.
- Include the picture of your simulation of your favorite program.
- Describe the hardware testing you undertook to prove the circuit works.
- Include a description, and pictures, of any extensions.
Give your wiki page the label cs232S17project5.
Put your VHDL files in your private subdirectory on the courses server.