ECE 5725 Homework 2

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Homework 2
1. What is the difference between a Linux pipe and a FIFO (or a named pipe)? What
can you do with a FIFO (named pipe) that you cannot do with a pipe?
2. In Lab1, we used the guide “Using a fifo with mplayer” currently linked in the
‘Guides’ section of blackboard. This guide is based on a link noted at the end of the
document. The link, https://milesalan.com/notes/mplayers-fifo/, also describes the
use of a fifo with mplayer however it has one very confusing aspect. What is the
source of the confusion that makes this guide a bit challenging to understand?
3. List all the pins on the R-PI GPIO connector used by the piTFT screen. Explain what
each pin is used for by the piTFT.
4. For the R-Pi 4, Model B, list all possible GPIO pins that may be used for projects and
labs. Identify the maximum set (when not using any special functions). Also, list the
minimum set, when all special functions (and the Adafruit 2.8 inch piTFT) are used.
5. In Lab1, a shell script named “start_video” was created to run mplayer and
video_control.py by using a single command. What is the correct ordering of operations
within this script in order to this shell script to terminate correctly? Comment on the
order of the calls within the script as well as which operation should run in the
foreground and which should run in the background. Hint: Correct shell script operation
should return to a command prompt (the $ in a command window) if everything
completed in the correct order.
6. If you run the date command on the ECE5725 server, the date and time are accurate. The
RPi does not have a battery-backed real-time clock so how does the RPi maintain
accurate time? When would it be appropriate to add an external, battery-backed real-time
clock to the RPi?
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7. For the following RPi GPIO circuit, describe why R2 is necessary in the figure:
Describe a possible ‘software situation’ that would damage the GPIO without R2. How
does R2 prevent the problem? Why is the value of 1k ohm selected for R2?
8. In Lab1 and Lab2, you use a python code video_control.py, for example, to respond to
buttons connected to the RPi GPIO pins. video_control.py passes these events to an
instance of mplayer, controlling the video under playback. The two processes
communicate using video_fifo. mplayer and video_control.py are launched from the
bash script, start_video.
Describe what would happen if start_video is run WITHOUT first creating the fifo
video_fifo. In this special case, if you press a button, what it the response of
video_control.py? What is the response of mplayer? Will video_fifo be correctly
created? Will control of mplayer be correct?
9. While using the PiTFT buttons to control video, you may have encountered a problem
with some of the buttons. It might appear that you had several ‘hits’ of the buttons when
you pressed the button only once. There are several causes for this issue; what is one
problem that could cause this issue? (hint: there are at least three possibilities observed
by teams in the lab).
10. Describe pygame screen elements including a surface and a rect. How are these used to
animate an image? Draw a step by step diagram illustrating the process of animating 2
frames of an animation on the PiTFT.