Lab 4 - Moore Elevator Controller

Lab 4 - Moore Elevator Controller#

Overview#

This lab is all about designing complex systems! You will do this by integrating sequential and combinatorial building blocks to design, test, and debug the Basic Elevator Controller from ICE5 before expanding functionality to an Advanced Elevator Controller.

In order to accomplish this, you will need to integrate modules from previous in class exercises and labs. Start now and make steady progress!

Authorized Resources#

For this lab, you may work in teams of two (including the prelab). If you worked in a team for Lab 3, you must work with a different partner for this lab.

You may seek help from any cadet or instructor, not limited to this course, and reference any publication in its completion. Online resources are acceptable. However, no resources containing solutions to the course homework, labs, exams, quizzes, or in class/out of class exercises are allowed.

Your work (and your code) must always be your own. Normal documentation of all resources utilized is required.

Lab Flow#

This lab iterates to first implement a Basic Elevator Controller, and then expand that to an Advanced Elevator Controller.

Basic Elevator Controller#

The initial phase of the lab only implements ICE5 Basic Elevator Controller, shown in Fig. 43

../_images/lab4_basic_controller.png

Fig. 43 Basic Elevator Controller user interface#

  • The elevator’s current floor is shown on the second seven-segment display

  • The elevator takes 0.5 seconds to move between floors

  • The display updates according to the output

  • The elevator must not teleport… no skipping floors

  • Three push buttons are to be used for resets

  • The Master Reset button resets both the FSM and the clock.

  • The reset floor is floor 2.

  • LED 15 must be tied to the clock signal that drives the FSM.

  • You may use the other LEDs for debugging. For example, outputting the current floor in binary. Otherwise they should be grounded.

This is the functionality who’s schematic you must design in the prelab.

Advanced Elevator Controller#

The final phase of the lab expands the basic functionality, see below.

This functionality should not be “hooked-up” in the Prelab. However, the top level entity will reflect this advanced functionality from the start.

Prelab#

Create a Top Level Schematic showing your architecture and submit one submission per team on Gradescope.

This schematic must only cover the Basic Elevator Controller functionality. You will be expected to update the schematic prior to implementing the Advanced Elevator Controller.

This schematic should consist of the top_basys3 entity, its I/O, the various modules inside it, and the connecting signals and logic.

The top-level entity in top_basys3.vhd will be:

-- Lab 4
entity top_basys3 is
    port(
        -- inputs
        clk     :   in std_logic; -- native 100MHz FPGA clock
        sw      :   in std_logic_vector(15 downto 0);
        btnU    :   in std_logic; -- master_reset
        btnL    :   in std_logic; -- clk_reset
        btnR    :   in std_logic; -- fsm_reset

        -- outputs
        led :   out std_logic_vector(15 downto 0);
        -- 7-segment display segments (active-low cathodes)
        seg :   out std_logic_vector(6 downto 0);
        -- 7-segment display active-low enables (anodes)
        an  :   out std_logic_vector(3 downto 0)
    );
end top_basys3;

The entity contains ports you will not use for the Basic Elevator functionality, but leave them in the schematic because you will need them for the Advanced Elevator.

Warning

Changing interfaces incurs massive engineering costs. This is because interfaces are the promises you make to external systems.

Even though we want to iterate (rather than “hit a home run”), we save a lot of time by making our I/O large enough for advanced functionality from the start. Imagine if you had to change the size of a std_logic_vector each time you wanted to tweak something.

But there is a cost! First, this requires additional hardware that may never be used. Second, you may waste effort solving problems that don’t actually need to be solved because by the time you get to it the project requirements may have changed or the implementation strategy may have changed.

Long story short, these sorts of decisions are hard and why Engineers get 💰

You need to include a clock divider module, and the remaining modules you need will come from your previous in-class exercises and labs (MooreElevatorController and sevenSegDecoder).

  • Do not hand draw the schematic; rather, use a tool such as Excalidraw, draw.io, or PowerPoint.

  • The components inside your top level should remain black boxes. The expectation is you will update this schematic at the end of this lab to reflect your final design.

  • Label all wires not connected to the top-level entity ports. These will be additional signals you will create in your VHDL code.

  • Only turn on seven-segment display 2 (display 0 is the far right). Force the others OFF by disabling their anodes. Reference earlier activities regarding how to turn on/off displays.

  • LED 15 must be tied to the clock signal that drives the FSM.

  • You may use the other LEDs for debugging. For example, outputting the current floor in binary. Otherwise they should be grounded.

  • Just like in the last lab, the clock divider uses generics so that you can redefine characteristics at instantiation. For instance, you can redefine the number of times the clock divider divides a clock for each instance of the module. Be sure to specify the value for your clock divider to obtain 2 Hz. For an idea on how to accomplish this, look at the generic mapping of the clock divider in ICE4 and Lab 3.

  • All component names should match the labels given to them (ex: elevator_controller should be labeled elevator_controller)

  • All components should have their internal ports labeled so it is clear what a signal is being connected to.

Lab#

  • Fork and clone Lab 4.

  • Open the project by double clicking elevator_fsm.xpr.

Tip

Much of this code can be extracted from previous projects. Rather than open another Vivado project (and the confusion that comes with it), we suggest you view your previous project’s GitHub repository in your web browser.

Basic Functionality#

First, directly implement the pre-lab scematic.

Add files#

You will need to add VHDL files from your previous labs and ICEs to the project. Reference Manually add files to Vivado Project

You need to add any design sources that you plan to bring in as a module. You do not need to bring in the testbench for these modules, since we have tested them in previous labs. However, you can if you’d like.

Complete top level#

Using your Prelab drawing, complete the top-level module. Remember this basically involves:

  1. Copying in component definitions

  2. Creating additional signal wires

  3. Instantiating your component instances and connecting all wires

For the clock divider, what value for k_DIV do you need to produce a 2 Hz clock?

Simulation#

A brief discussion on testing philosophy.

The type of testing you choose results in a tradeoff of complexity vs. how much confidence your test gives you that your design works.

Each component within your top_level already has been simulated and tested. This is known as unit testing because you make sure that each unit (component) does what it is supposed to. Unit tests give you confidence that a single thing works and they are quick to write and run. But unit tests don’t give you any information on how components will or won’t work together.

Integration testing tests if multiple units work together; for example, does the clock_divider indeed provide a slow clock to the FSM? While this type of testing is awesome for software design, it’s difficult to do in hardware design. Rather than use a VHDL simulation, we have done our integration testing in previous ICEs and Labs by actually squirting to hardware. This is more complex and takes more time than unit tests do, but in turn we get greater confidence that the system works.

For Lab 4, the only thing that isn’t already tested is if the entire thing works! This type of testing is end-to-end testing. If the test passes then we know the entire system works. Unfortunately, end-to-end tests are also very complex to design and maintain. Because of this you do not need to write a simulation test bench for this lab.

As engineers, part of our job is to determine what is the appropriate level of confidence and justify designing tests to meet that level. For this particular application, the cost of simulating an end-to-end test is too high, so we will debug on hardware (yikes!).

Deliver#

  • Don’t forget to uncomment lines in you XDC file.

  • Generate bitstream and program device!

  • Show it to your instructor

  • Commit to git and tag (see below)

Demonstrate your basic functionality to your instructor.

After you have demonstrated basic functionality, you want to make sure you save that result in case you ever need to go back to it. To do this we will use git tag.

The normal flow:

  1. Type git status to see the current state

  2. Add all hardware files with git add src/hdl/*.vhd

  3. Add your constraints file with git add src/hdl/*.xdc

  4. Add you .xpr file.

  5. Add any other files you need to commit (like your bitstream)

  6. Run git status again to make sure you are good.

  7. Commit and push!

  8. Make sure your github action looks good

Note

Because we did not make a testbench to run, the GitHub Action simply runs GHDL Synthesis

This is an experimental feature.

Now for the annotated tag. The -a tells git to expect a message. The message can be whatever you’d like, but please be sure to tag as basicFunc.

git tag -a basicFunc -m "Four floor controller"

Now push the tag to GitHub

git push --follow-tags

You should now see the tag in your repository.

../_images/lab4_git_tag.png

Fig. 44 A tag saved in a GitHub repository#

You can go back to this saved point at any time!

git checkout basicFunc

The point of a tag is that you cannot edit the branch. If for some reason you need to… use Google.

Push your tagged basic functionality to GitHub.

Advanced Functionality#

After demonstrating your basic functionality and after pushing your basicFunc tag to GitHub, it is time to implement advanced functionality!

  • The elevator will travel from floor 1 to floor 16

  • Use the two left-most digits of the display to show the floor in decimal

  • All other functions will stay the same as in Basic Elevator Controller.

Hint

Revisit ICE6 for using TDM to drive a seven segment display.

Reference Basys3 Seven Segment Display

Before you start to code, update your schematic. This schematic will be submitted in the Lab 4 Report.

(Optional but recommended) Show your schematic to your instructor

After you have finished your schematic, make it work!

Implement advanced functionality and demonstrate to instructor.

Commit & push your changes.

Push changes for advanced functionality to GitHub.

Deliverables#

Below are the deliverables and point distributions for the Lab 3:

Deliverable

Points

Prelab

20

Basic Controller Demo

10

Advanced Demo

30

Passing GitHub Action

10

Written Report

30

The 2 page max report will be very similar to Lab 3 Report requirements, with the following changes:

Things to Exclude:

  • Do not include RTL schematics or discussion

  • There is no need to include a waveform

Things to Add:

  • Share your thoughts on modularity and abstraction

  • Discuss how your schematic changed (and what stayed the same) between Basic and Advanced Controllers

  • Discuss how you used TDM to get the Seven Segment Display functioning

  • How did you handle binary to decimal conversion for two displays?

  • What is the problem with the MASTER RESET?

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