Description
User Space stuff
Sometimes it is easier and/or better to not have more code inside the kernel space – this may be for
easier debugging, access to other libraries, or other specific reasons. Using a part of the system call
interface we can cheat a bit and get access to the kernel’s memory space at the user level.
Those Blinking Users
This can be done in any number of user level programming languages, but we recommend you stick
with C so that we can better help you. Your user program needs to:
1) Find one of the ethernet devices in your Virtual Machine (perhaps e1000?) and map the
appropriate BAR
2) Save the current LEDCTL value and print it for the user to read
3) Turn the LED2 and LED0 LEDs on for 2 seconds
4) Turn all LEDs off for 2 seconds
5) Loop 5 times and turn each LED (LED3, LED2, LED1, LED0) on for 1 second
6) Restore LEDCTL to initial value
7) Read and print the contents of the Good Packets Received statistics register
8) Clean up and exit
Run this program a couple of times while e1000 is loaded in the Virtual Machine to see if you can
catch any packets being sent and counted by reading the Good Packets Received register. Also run this
with ledmon from Assignments 3 and 4 to verify the LED’s are properly blinking. Remember that you
can run this user program while the original driver is still loaded, as long as you don’t do something
that conflicts and confuses the driver. You can even do this on some other hardware if there’s an LED
to blink.
The Blink is over
Turn in these materials before 11:59pm Wednesday, 20-May-2020:
1. Source code to your user program, Makefile, and any scripts used.
2. Note that you won’t need to unload the existing kernel network driver to run this program. Give a
short explanation what this might imply.
3. A typescript of the user program running at least three times (partly to try to catch the packet counter
changing)
