EECS 373 Winter 2004 -- Homework 1
		Reading and understanding specifications: USB

Due at the _start_ of class, March 16th, 2% of course grade.  

GOAL
This homework assignment is designed to teach you to read specifications.
You will also learn about the USB (Universal Serial Bus) specification. 

REFERENCES
* http://www.beyondlogic.org/usbnutshell/usb1.htm  
    -- Explanation of the specifications
* http://www.usb.org/developers/docs/
    -- Specifications themselves
* USB explained, S. McDowell, M. Seyer, 1999.  
    -- Dead tree explanation of specifications (a bit simplified)
* http://www.nti1.com/usb-prots.html
    -- Short details on transactions.

You should find the first reference the most useful though the last is worth
briefly looking at too.  Of course you might also find other web pages or
books that are also useful.

NOTE ON HOMEWORK
On the whole your answers should be in your own words.  You should not be
using words you don't know the definition of.  However, you may quote from the
above works or any other.  But be sure you are making it clear exactly what
you are quoting and where you are quoting it from.  Not doing so will result
in a reduced (or zeroed) grade on this homework and, in extreme cases may
result in a referral to the Honor Council.

QUESTIONS
Unless otherwise noted these questions can each be answered in a sentence or
two.

1. Wires (25%)
  a) How many wires are used in a USB cable?  Briefly describe for what each 
     wire is used.
  b) In low-speed communication how is the "J" state represented? 
  c) USB usually uses "bit stuffing".  Explain why and exactly when a stuffed
     bit is inserted.
  d) Using the rules of low-speed communication (including bit stuffing) DRAW
     the data wires for the following "raw data" "111111110110"
     

2. Speeds (15%)
   a) In 1.x of the specification only two bus speeds were allowed.  What are
      those speeds called and what is their maximum bandwidth?
   b) In version 2.x of the spec. a third speed was added.  What is it called 
      and what is its bandwidth?
   c) What is the advantage of supporting multiple speeds in the USB 
      specification?

3. Protocol (20%)
   a) In USB terminology, what is an "endpoint?"
   b) For the lowest speed, how is a "start of packet" (also called "sync") 
      indicated?
   c) How is an "End of packet" indicated?  Be specific (i.e. don't use terms 
      you don't understand...)

4. Misc. (20%)
   a) Why does USB support two different types of connectors?
   b) When a USB device wishes to perform an interrupt how is this 
      communicated to the host?
   c) What is an Isochronous transfer?  Why are they used and how are they
      different than bulk-data transfers?

5. Putting it all together (20%)
   a) Assume you had a host that wanted to move 10GB of data to a USB device..
      Take your best guess about the expected amount of time this would take
      for the highest speed communication allowed under version 1.x of the
      specification.  How about 2.x?  Be sure to include protocol overhead and
      explain exactly how you arrived at your number.  (This will probably
      take 2-3 paragraphs for a good answer.)  Relate this back to an actual
      measurement using a real USB device.