>Why do none of these mods simply change the SA110's internal clock
>frequency multiplier?
Because there are other chips in the Newton that expect the signals they handle
to be synchronous to the main clock. Which they wouldn't be anymore if you
just accelerated the clock of one particular chip.
Imagine you just started a business that sells MP3 CD's. People send you
a list of hits they want and you burn it. Thus no two CD's are
alike.
To make things easy, let's assume this requires two assembly lines:
The one for the CD itself and the one for the label.
Plus one guy who glues both together.
Creating the CD itself is done by assembly line A (the 2x00 voyager chip):
A1) Grab a blank CD from the box
A2) Burn it
The label is taken care of by assembly line B (the 2x00 ARM processor):
B1) Grab a sheet from the box
B2) Print the titles on it
B3) Cut off the edges so it'll be round
B4) Put glue on the back
Once both assembly lines are finished, you can
5) Glue the label onto the CD
What you do now is buy a rectangular table and 7 chairs.
You put two chairs at one of the long sides for assembly
line A and four at the opposite side for assembly line B.
The seventh is placed at the short side close to A2 and
B4.
Now you hire 7 people and place them on the chairs,
ordering them to do their respective tasks.
You find very soon that your employees, probably because
you can't pay that much, aren't too smart. Each can do
his task just fine, but they are all unable to grasp when to
start. The text is printed on the table instead of on the
paper because the paper isn't ready yet, the glue is smeared
on the table instead of on the paper because the printer
hasn't finished, the guy responsible for burning the CD
puts air in the burner because the guy who gets
the blank CD's out of the box hasn't delivered yet.
Well, you think, this isn't the way to go. We need some kind
of synchronization if we ever want to be successful.
So you hire another guy whose only job is to shout
"Now" once every second.
His name will henceforth be "Clock".
The other 7 are well capable of completing their tasks within
a second, and from now on they begin it as soon as they
hear a "Now".
All would live happily ever after if there wasn't that darn
problem that assembly line A needs only two seconds to finish while
assembly line B needs four. As the guy on the small table side
(the guy with the glue) needs a CD and a label at the same time,
the obvious way to go would be to have him wait until assembly
line B has finished. But you just
instructed him to glue on every "Now", so this isn't an option.
Another solution would be to hire another two people for
assembly line A who do
nothing but pass the CD on when they hear the "Now".
Reluctantly you hire the two, and all works just fine.
Eventually, though, you notice that your competitors are
much more successful than you are. And you try to reduce
manufacturing costs.
The first attempt, as usual, is make everybody work faster.
So from now on the Clock guy shouts "Now" every 0.5
seconds, increasing output by 100 percent.
This is what happens if you replace the crystal.
Eventually, though, your shouter requests a salary
rise. After all, he is shouting twice as often as
before. But you don't have the money, so, grudgingly,
you order him to shout with the old frequency again,
once every second.
Thinking... thinking...
Ah! Another good way to save costs is by getting rid of
people who aren't doing any real work. Like the two
guys in assembly line A who do nothing but pass the
burnt CD on. But you can't just fire them for the
very reason you hired them for in the first place.
Here comes Frank and says: "Hey! Did you notice that
burning CD's takes much longer than any step needed
to make the label? In fact, about twice as long? In other words,
have you noticed that everyone in assembly line B can do his
particular job in well under half a second?"
You are deeply impressed, fire the two people from
assembly line A who pass the CD's on and hire another shouter instead.
His job is to shout "Do it" twice for every "Now" he hears
from the other shouter.
The second shouter's job name henceforth is "Multiplier".
You make
sure that from now on Assembly line A only hears the
"Now" and Assembly line B only hears the "Do it".
Miraculously, from now on the guy at the end of the
table gets both a burnt CD and a prepared label at the
same time twice as often as before, and within months your
competitors are out of business. Except one.
This can be compared to the Newton in its
original state (well, kind of, please ignore the "competitors
out of business" part...).
As a matter of principle, you want to get rid of the
last competitor. So you remember Frank's brilliant
idea of doubling the speed of assembly line B.
"Why not triple it?", you think, and advise your
Multiplier to shout "Do it" three times every second
instead of two times, starting tomorrow. You even
accompany that by a salary rise for the Multiplier
guy because the Venture Capital people have finally
noticed your success and you can afford it.
For assembly line B you have now increased the speed
by 50 percent. However, the clock guy is still shouting
his "Now" once every second as before.
Next morning, the guy responsible for glueing has
quit because he wasn't able to do his job anymore.
Although both assembly lines still work perfect, burnt CD's and
prepared labels just don't reach him at the same time anymore...
Cheers
Frank
Newton hardware and software at http://www.pda-soft.de
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