Here are the details about the second small-group activity for the course.

This activity must be completed using "submit" and Piazza.

The initial submission as well as the final answer/summary of the
discussion in your group must be made using "submit". For your initial
submission, i.e., your initial answer to the problem specified below,
use the following command:

    submit c3430aa a21 myInitialAns.txt

where "myInitialAns.txt" is the name of the file containing your initial
submission. It *must* be *plain text*, not .pdf or .doc etc. 

AGAIN: your file must be plain text, not .doc etc. If you normally use, 
for example, MS Word, save your file as plain text and submit that file.

For your final submission (your final answer to the same problem *and*
summary of the discussion in your group), use the following command:

    submit c3430aa a22 myFinalSub.txt

where "myFinalSub.txt" is the name of the file containing your final
submission. Again, it *must* be *plain text*, not .pdf or .doc etc. 

The discussion portion of this activity will be on Piazza. Following
the deadline for the initial submission, students will be arranged in 
groups of about 4 each, based on those initial submissions. Once these 
groups have been formed, you will receive email to that effect. After
that, when you log into the Piazza site for the course, you should see 
your group and posts from everyone in that group but won't be able to
see posts in other groups. The idea is that you will engage with the
other students in your group in a discussion about the problem. But 
unlike in CONSIDER, there won't be any "rounds" etc. You will just be
expected to participate in a reasonable discussion in your group. 

But one important point to stress is that if you fail to make your initial 
submission on time, you will not be assigned to a group and will not be 
able to participate in the discussion. Essentially, you will get a 0 for
the activity.

=============
The timeline for the activity is as follows:
Activity assigned: Wednesday, 4/20, 7:00 pm
Initial (individual) submissions due: Thursday, 4/21, 11:59 pm
Small-group discussion starts: Friday, 4/22, at 12 noon
Group discussion ends: Sunday, 4/24, 6 pm (no "rounds")
Final (individual) submissions due: Monday, 4/25, 11:59pm

=============
This activity will be worth 15 points. 

Your individual score will be determined as follows:
a. Completing the initial submission and the other activities by the
   respective deadlines: 2 points.
b. Effectiveness of participation in the two "discussion" rounds: 3 pts
c. Correctness of your (individual) final answer: 5 pts
d. Quality of your (individual) summary of the discussion in your
   group: 5 pts

==============

Here is the (2-part) problem:

a. Most current systems have a "kernel" mode and a "supervisor" mode.
Would you expect a CPU used in an *embedded* system (such as a camera
or the steering control mechanism of a car) to have such modes? 
Explain why or why not.

b. We said that while there are some similarities between XOPs and 
interrupts, they are fundamentally different mechanisms. Briefly
explain the similarities and why, desipite these similarities, they
are essentially different mechanisms.

=================

Again, make your initial submission using the following command:

    submit c3430aa a21 myInitialAns.txt

where "myInitialAns.txt" is the name of the file containing your initial
submission. It *must* be *plain text*, not .pdf or .doc etc. 

Your submission is due by 11:59 pm tomorrow (Thursday, 4/21).

=================

Answers:

a. We would not expect embedded systems to have a kernel mode in
contrast to a user mode. A major difference between a "regular"
computer and an embedded system is that a regular computer is intended
to run arbitrary *user* programs which may contain all kinds of bugs
that the system has to be protected against. An embedded system is not
(typically) designed for that. It simply runs the program that the 
manufacturer loaded into it (and possibly updated it relatively infrequently) 
so there is no such risk to guard against. So there is no need for two
distinct modes.

b. The key difference is that an XOP is a "system call". That is, a user
program wants to perform an operation that needs special privileges and can 
only be performed by the OS (in kernel mode); e.g., creating a new directory.
So the user program contains the appropriate XOP call.

By contrast, an interrupt is something that happens when an external event,
such as input arriving from a keyboard, happens. When such an event happens,
an interrupt signal is "raised" and the CPU will, when it completes execution
of the current instruction, save the PC and the PS and jump to the interrupt
service routine. There is no call to the interrupt service routine in the 
program being executed; that program doesn't know when the interrupt will 
happen. Instead, its execution gets interrupted (by the arrival of the 
interrupt and the execution of the interrupt service routine) and will be 
resumed once the interrupt service routine finishes execution.