Friday, October 29, 2004
At least my students have social consciences...
And they weren't asleep either.
I promise that there is a funny story buried in here somewhere. Read on to be edified and entertained.
One of the "interesting" aspects of teaching technical subjects is the fact that many non-technical words take on different meanings in the context of some technical topic.
Today in Digital Design class, I was talking about the process by which a designer makes a state assignment in an asynchronous sequential state machine. For those of you who aren't asleep after reading that last sentence, you can think of an asynchronous state machine as being like a game of fetch:
The problem is that we can't expect the state bits to transit from 00 to 11 at the same time. One of the bits has to change first. But notice that if the state goes from 00 to 10 before it tries to go on to 11, it won't get out of 10, because that state is stable. If it goes from 00 to 01 before it tries to go on to 11, it won't get out of 01 for the same reason. In digital design, we call this a race, because the bits are almost quite literally racing to see what results. The above race is a critical race, because there is at least one way for the race not to be settled the way that we want. Without presenting an example, we could develop the idea of a non-critical race, where regardless of the way the race is settled, we get from the initial stable state to the desired final stable state.
Here comes the punch-line. Take in the previous discussion, and now put yourself in the place of my students (who know I'm sort of a cut-up at times) to see just why this statement rates a 10 on the Uninententional Comedy Scale...
As you can well imagine, I was absolutely mortified, but only after the little man in my brain rewound the tape so I could figure out just what I'd said that had provoked such shocked entertainment. Class quite literally came to a standstill for a few minutes.
Those of you who would specifically know me by looking at me will appreciate the way in which I "recovered":
So even though I'm a racist, I'm still voting for John Kerry. Some of you out there might seek to generalize such a racist attitude to all Kerry voters. Save it. Since I presumably still have you held hostage at this point in the post, you should instead invest your energy into telling me who you think will win the election...along with a few other details, of course.
"Thoughts" on that subject are due before the polls open next Tuesday. I'm in the midst of trying to get some "celebrity" entrants. Stay tuned to see how those efforts pay off.
Once again, happy predicting, and remember to vote!
|
I promise that there is a funny story buried in here somewhere. Read on to be edified and entertained.
One of the "interesting" aspects of teaching technical subjects is the fact that many non-technical words take on different meanings in the context of some technical topic.
Today in Digital Design class, I was talking about the process by which a designer makes a state assignment in an asynchronous sequential state machine. For those of you who aren't asleep after reading that last sentence, you can think of an asynchronous state machine as being like a game of fetch:
Mildly-labored metaphor alert!There are all sorts of problems with using and designing asynchronous sequential circuits, because they are inherently unstable. One issue pertains to the digital codes that are assigned to certain states. A stable state having code 00 might need to be followed by one having code 11 as the result of some input change. But the same input change might find other final stable states, perhaps the ones having codes 01 and 10.
Suppose that in a game of fetch, you're holding a stick that your dog is waiting for you to throw. As long as you hold the stick, the dog will wait for you to throw it. This is a representation of a stable state - as long as no input change occurs, the state will cause itself to occur continuously. At the moment you throw the stick (here, an input change) the dog might spend a moment in the state where he is still waiting for you to throw it. This state is not stable, because as soon as the dog realizes that the stick has been thrown, he will take off running after it. Thus, the input change (throwing the stick) causes a momentary unstable state (the dog still waiting for it to be thrown) before causing a new stable state to be reached (that of the dog running after it).
The problem is that we can't expect the state bits to transit from 00 to 11 at the same time. One of the bits has to change first. But notice that if the state goes from 00 to 10 before it tries to go on to 11, it won't get out of 10, because that state is stable. If it goes from 00 to 01 before it tries to go on to 11, it won't get out of 01 for the same reason. In digital design, we call this a race, because the bits are almost quite literally racing to see what results. The above race is a critical race, because there is at least one way for the race not to be settled the way that we want. Without presenting an example, we could develop the idea of a non-critical race, where regardless of the way the race is settled, we get from the initial stable state to the desired final stable state.
Here comes the punch-line. Take in the previous discussion, and now put yourself in the place of my students (who know I'm sort of a cut-up at times) to see just why this statement rates a 10 on the Uninententional Comedy Scale...
"And so, from the previous example [one where both a critical race and a non-critical race are presented, without those specific terms being used] we can see that not all races are created equal..."Let that one hit you in face for a moment...
As you can well imagine, I was absolutely mortified, but only after the little man in my brain rewound the tape so I could figure out just what I'd said that had provoked such shocked entertainment. Class quite literally came to a standstill for a few minutes.
Those of you who would specifically know me by looking at me will appreciate the way in which I "recovered":
"Right now, I'm blushing, but none of you can see it through the content of my character." (The end of the comment being accompanied with a pinch-and-pull of the melanin-rich skin on the back of my other hand.)That also provoked intelligent amusement. In the end, several good laughs were had by all, including by myself - even if mine were in some spite of myself.
So even though I'm a racist, I'm still voting for John Kerry. Some of you out there might seek to generalize such a racist attitude to all Kerry voters. Save it. Since I presumably still have you held hostage at this point in the post, you should instead invest your energy into telling me who you think will win the election...along with a few other details, of course.
"Thoughts" on that subject are due before the polls open next Tuesday. I'm in the midst of trying to get some "celebrity" entrants. Stay tuned to see how those efforts pay off.
Once again, happy predicting, and remember to vote!
|
