EECS 270: Lab 3

Overview

This lab has two in-labs due in successive lab periods. In the first period you will demonstrate your solution to the first design problem, and in the second, you will demonstrate your solution to the more complex problem.

Preparation

• The combinational Verilog reference, found on the lab webpage, will be needed.
• You may find reviewing the sections of the text related to combinational logic (4.1-4.3) to be useful.
• Having an understanding of Comparators (6.9 of the text) may help.

Verilog issues

• Module declarations.
• Declaring parameters as input or output.
• Declaring variables as wires.
• Instantiating other modules.
• Using assign statements. These assign statements may only include AND (&), OR (|), XOR (^), and NOT(~). You may not use any other operators (such as ">", "<, and "?:").

Design Specification

Robbie the Robot

Robbie is the simpler robot which is attempting to drive to the beacon and stop. Robbie has three sensors and two independently controlled wheels. The sensors are mounted on the front, front-right and front-left of the robot, as seen in Figure 1. These sensors detect if the beacon is in a certain area (the cones indicated in Figure 1). If the sensor does detect the beacon it outputs a "1", otherwise it will output a "0".

The two wheels are driven independently. If a "1" is sent to the wheel it turns forward, but if a "0" is sent to the the wheel it doesn't turn. Robbie will go straight if both wheels are turning forward, and will stop if both wheels are stopped. In addition, Robbie turns right if the left wheel is going forward while the right wheel isn't turning, and would turn left in the symmetric case (the left wheel stooped and the right wheel going forward).

Robbie should follow the following rules:

• He is to go straight if the forward sensor detects the beacon and/or both the left and the right sensors detect the beacon.
• Otherwise, if either the right or the left sensor detects the beacon, he is to go in that direction.
• Otherwise, he is to stop.

Figure 1: Robbie the robot, with sensors and wheels.

Implementation details

You are to implement Robbie twice: once using the schematic editor, and once using Verilog.

Schematic version


For your schematic design, you are to use dip switches 2, 1 and 0 as the left, forward, and right sensor inputs respectively. You are to turn on the red LED #1 to indicate that the left wheel is going forward, and turn on red LED #0 if the right wheel is going forward. Otherwise those LEDs should be off.

Verilog version


For the Verilog design the inputs should be the same, but you outputs will be different. Instead of using red LED #0 and #1, you will instead use the seven-segment displays. You should display a capital "F" on HEX0 if the right wheel is going forward, and a capital "S" if the right wheel is stopped. You should do the same on HEX1 for the left wheel. Recall that the HEX segments are active low.

For the Verilog design, you must use the following module declaration as your top-level module (which should be named robbie.v):

module robbie(ls,fs,rs,lwd,rwd);
  input ls,fs,rs;
  output [6:0]lwd,rwd;

Further, you must make a second module (it can be in the same file) which handles the display of a "S" or "F" to hex display. It should take one input, which indicates if it is to display an S or an F, and should generate a bus of 7 wires as output. You can then instantiate that module twice, once for each hex digit. See the Verilog combinational reference for examples of doing this.

Renee the Robot

Renee is similar to Robbie, but there are some significant differences. First, she has only two beacon sensors (left and right), but those sensors provide information about distance. Secondly, she has bumper sensors (which tell her if she has hit something). Lastly, her wheels can go in reverse in addition to going forward. These changes are detailed below:

1. Beacon sensors:
   Renee uses two more sophisticated sensors in place of Robbie's three sensors. The one on the front is removed. The sensors provide information about how strong of a signal they are getting from the beacon. The sensors return a 3-bit unsigned number. The closer the beacon (and more toward the center of the cone of a given sensor) the higher the value they return.

2. Bumper sensors:
   Renee has four of these, one on the front, left, right and back. They return a "0" if Renee has bumped into something in that direction, and a "1" if she has not.

3. Wheels:
   Renee's wheels can go forward and backwards as well as stopping. She can now do the following actions:

   Action	Left Wheel	Right Wheel
   Forward	F	F
   Left	S	F
   Right	F	S
   Stop	S	S
   Hard Left	R	F
   Hard Right	F	R
   Left Back	S	R
   Right Back	R	S
   Reverse	R	R

   
   Table 1: How Renee uses her wheels to perform her actions.
Renee's interactions with the world
Renee should head in the direction of the sensor which indicates it has the strongest signal. If both signals are zero Renee should stop. If the two signals are the same, Renee should go forward. However, the beacon senors are ignored if Renee has hit something: in that case her first priority is to move away from the thing she hit. If any of her bumpers detect a collision, she should follow the these rules:
• If her front bumper sensor is the only one detecting a collision she should move in reverse.
• If her back bumper sensor is the only one detecting a collision she should move forward.
• If her left bumper sensor is the only one detecting a collision she should move right back.
• If her left and front bumper sensors are detecting a collision she should move right back.
• If her right bumper sensor is the only one detecting a collision she should move left back.
• If her right and front bumper sensors are detecting a collision she should move left back.
• If her left and back bumper sensors are detecting a collision, she should move right.
• If her right and back bumper sensors are detecting a collision, she should move left.
• If any two bumper sensors on opposite sides are detecting a collision (front and back or left and right) she should stop.

Implementation details


For the Verilog design, you must use the following module declaration as your top-level module (which should be named renee.v):

module renee(ls,rs,fb,rb,lb,bb,lwd,rwd);
  input [2:0] ls,rs;     //Beacon sensors
  input fb, rb, lb, bb;  //Bumper sensors
  output [6:0]lwd,rwd;   //wheel outputs

You should use the DE2 board inputs as follows:

Sensors	Board inputs
Right beacon sensor	SW2-SW0 (SW2 is MSB)
Left beacon sensor	SW6-SW4 (SW6 is MSB)
Left bumper sensor	Key3
Front bumper sensor	Key2
Back bumper sensor	Key1
Right bumper sensor	Key0


Table 2: Mapping of sensors to switches for Renee.

Notes:

• The bumper sensors should be treated as detecting a collision if the corresponding key is pressed. (Recall that the Keys are active low.)
• For outputs you should again use HEX0 and HEX1, displaying an "F", an "S" or an "r" (r is displayed by having segments 4 and 6 lit).
• Again, you may only use the same subset of Verilog we allowed for Robbie.

Design Notes and Hints

• Drawing a truth table for Renee is pretty much impossible. There are 10 inputs (6 bits from the beacon sensors, 4 from the bumper sensors). That would give you more than 1,000 rows. So your design will have to be more ad hoc. You may want to draw a truth table for certain parts (say the bumpers) however.
• For Renee you could just write logic equations for each output directly, but that will make things very difficult. Instead you should consider writing equations for intermediate results and then using those to generate the correct results. Think carefully about what intermediate results you want. This decision will have a huge impact on how difficult the lab is.
• For Renee you should probably use a module to manage your HEX displays as we required for Robbie.
• The HEX display modules for Robbie and Renee are quite short. Because we don't allow conditionals in this lab (if statements) you are forced to write logic equations for each segment. For Robbie you can do the logic for each segment with only a constant or a single literal.
• While a Karnaugh map is viable (and required for in the pre-lab) for Robbie, all it does is reduce the amount of typing/drawing. If you gave it something more complex (say the canonical sum-of-products) the tools would optimize it automatically. In fact, even when you provide the minimum sum-of-products, the tools might change that to something which maps more nicely to the hardware.

Deliverables

1. Pre-Lab (55 points)
   
   1. Draw a truth table for how Robbie's three inputs correspond to each of the two outputs (don't worry about the HEX displays, just the simple on/off of the LEDs). Then use a Karnaugh map to find the minimal sum-of-products for each of the two outputs. Show your work. (10 points)
   2. Turn in a printout of the schematic and qsf file for your schematic solution to the Robbie problem. (10 points)
   3. Turn in a printout of the Verilog and qsf file for your Verilog solution to the Robbie problem (including the display on the HEX digits). (10 points)
   4. Create and print a functional simulation which goes through all possible input combinations for Robbie (hints: #1 there are only 8 combinations, #2 use the clock input option with different periods). Have the simulation list the inputs and output in this order: left sensor, forward sensor, right sensor, left wheel (high if going forward), and lastly right wheel (high if going forward) and run it on your schematic version of Robbie. (10 points)
   5. We have provided an input test vector for you to use on your Renee model. Download it and load it into the simulator (as a text file it is pretty meaningless). This is what a good test should look like. You should be viewing it using the waveform viewer, that thing you've used to generate simulation test cases!

      Now, using our test as a model, write a test, using the waveform viewer (that thing you used to do tests in simulation) which tests the following cases. Provide a printout of the input waveform. (15 points)

      ls	rs	fb	lb	rb	bb
      001	010	0	0	0	0
      001	001	0	0	0	0
      101	101	1	0	0	1

2. In-Lab (60 points)
   The in-lab is turned in on two different days. On the first day of in-lab the two Robbie simulations are to be demonstrated on the DE2 board. (20 points) On the second day of in-lab, the Renee simulation is to be demonstrated on the DE2 board. (40 points)

3. Post-lab (35 points)
   
   1. Prepare your lab report as described in the EECS270 Laboratory Overview handout. Make sure you complete and include all parts of the report including the Cover Sheet and the Design Documentation section. Include your Verilog code and qsf file for Renee only.(10 points)
   2. Print the results of your Renee model on the test vector we supplied (in the pre-lab) as well as the test vector you wrote for the pre-lab. (10 points)
   3. Consider what would happen if Renee detected the beacon in front of herself (so left and right are equal) and was thus moving forward and then hit some barrier between herself and the beacon (with her front bumper). Answer the following questions (15 points)
      1. What would an observer see her do (over time).
      2. Would she ever reach the beacon? Why or why not?
      3. Renee, as described, maintains no state. That is, she only reacts to the current situation without any memory of the past. How could having state help in this case?