计算机网络试题,高校精选

Computer Architecture 2022-23

Assessed Exercise 1

— State Machine Circuit —

Introduction

The purposes of this exercise are to learn how to design a simple synchronous

digital circuit that implements a state machine, how to specify it in a hardware

description language, and how to test it via simulation. The specification and

simulation will use Hydra, a functional computer hardware description language.

The exercise

cuit, which should be included in TrafficLightRun.hs.

• There should be a main function in TrafficLightRun.hs that runs all of

your test cases.

Informal specification of the circuit

The circuits are traffic light controllers. There are two versions.

Version 1

The circuit controller1 has one input, a bit called reset. This would be connected

to a pushbutton. The reset button should be pushed once to start the circuit,

and then in normal use it would never be pressed again. We model this by

defining the value of the reset input bit to be 1 during the first clock cycle, and

through a fixed sequence: green, green, green, amber, red, red, red, red, amber,

and then it repeats.

1

Version 2

The second version, controller2, is intended for a pedestrian crossing. There

are three lights for traffic (green, amber, and red) and also two lights for the

pedestrian (wait and walk). There are two input bits: a reset pushbutton, and

a walkRequest which is 1 when a pedestrian presses the Walk pushbutton.

Normally the outputs indicate green/wait. However, when the walkRequest

button is pressed, the traffic light changes to amber, and then the traffic light

changes to red and the pedestrian light turns to walk for three clock cycles. Then

To summarise, the inputs are: reset (a pushbutton) and walkRequest (a

pushbutton). The outputs are: green, amber, red, wait, walk (each is 1 bit),

and walkCount (a 16-bit binary integer).

You may notice that the specification of the problem doesn’t say what to do

in a few subtle situations. For example, what should happen if the walkRequest

button is pressed when the system is in the red/walk state? You may adopt

any reasonable policy you like for these situations. In the real world, you (the

engineer) might go back to the customer to discuss what to do. It is common

for the requirements of a project to evolve during the implementation. Actually,

that’s one of the reasons that good engineering includes making your solution

button would be out where a pedestrian could see and press it, and the

various light outputs would control the actual light bulbs.

• In the real world the clock cycles would be too short, so each light would

be held for a larger number of clock cycles. For example, the amber phase

might last for a million cycles and green/red would be correspondingly

longer.

Work in small groups

This assessed exercise should be carried out in a small group consisting of two

to three students. Any amount of discussion and shared work within the group

is fine, and the product you hand in counts fully for each member of the group.