Paul G. Allen wrote:
Sigh. I have been hearing about the asynchronous processor thing for
the last 15 years. It is no closer than it has ever been.
http://www.arm.com/news/12013.html
So, they announced it this year. And the previous year. And the
previous year before that.
And 4 gazillion cell phones still ship with a clocked ARM9. Gee, I
wonder why? Perhaps because it's not a win?
Cell phones are *very* sensitive to power. If it were a win, they would
switch in one generation.
Most processors spend most of their time idle. Power consumption is not
the only reason to remove clock signals.
It's the main one. Modern processors spend 50%+ of their power just
powering the clock grid.
Running clock signals all over a chip is expensive in timing
(propagation delays), power consumption, physical space, and other
areas. One of the biggest problems with synchronous systems is the
propagation delays imposed upon the timing signals.
You call it a problem; I call it an advantage.
The clock provides a hard, temporal boundary. You must get done within
that time, or it's a bug. That is the task of engineering. Decoupling
a complex problem into manageable pieces.
Look at some of the most reliable software. Gee, things like vxWorks on
the Mars rover tend to use interrupts as a global "clock". I wonder
why? Perhaps because it serves as a temporal boundary and you can make
guarantees? Sound familiar?
Why hardware wants to be more like software in reliability is completely
beyond me.
-a
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