> (...) DSP (digital signal processing) chips are ideally suited
> for fast repetitive
> integer arithmetic, so programming a DSP to do JPEG can yield
> significant speedups." (from: JPEG image compression FAQ)
And there must be other functions of a keitai that would
benefit from a DSP, ones that aren't engaged while
browsing. It could filter incoming and outgoing
audio in different ways, for example, while the phone
was being used as....well, as a phone.
I might point out here that many DSP chips are also
crude-but-serviceable general purpose processors,
whose development kits typically come with C compilers
these days. There are even real-time operating
systems for DSPs. In graphics, Ivan Sutherland
called this The Wheel of Reincarnation: start with
a little hardware speedup, and years later, your
former accelerator pedal has been redesigned so
many times that it has turned into a whole
car in itself.
One might, for example, implement KVM on a DSP.
And a browser. And a ringtone player....for that
matter, with tightly-optimized pipelined integer
operations, you could do some pretty cool 3D
game animation....
This is not to suggest using a DSP in lieu of a more
common processor type - after all, modern power-
management features and fabrication technology
make it possible to put an awful lot of chips in a
phone, relatively few of which need to be doing
anything at any given time. Nothing really prevents
you from having a DSP and other processors
as well, in the same phone, as long as they aren't
all banging away at once, threatening to melt the
plastic. The main barrier is cost: nobody's making
money selling these phones at the moment. Ericsson,
for one, couldn't stand the heat, and has since left
the kitchen. If the Japanese seem undaunted, it's
because they're doing what they do best: hanging
in there, spending lots of low-interest capital from
their corporate group bank, building market share in
new categories of consumer electronics.
The most sensible approach here, if you need to
speed up JPEG decoding, is probably to use a
generic CPU core like ARM, and add a relatively
small subcircuit specifically for the more time-
consuming inner loops of JPEG decoding. Then
it's all on one chip, and still pretty cheap, assuming
you have reasonable production volume. Probably
you could rip off some design for low-end digital
cameras, stripping out the JPEG ENcoding part...
unless it's a phone that is *also* a camera, in
which case you're pretty much home free.
-m
leap@gol.com
[ Did you check the archives? http://www.appelsiini.net/keitai-l/ ]
Received on Wed Mar 14 15:31:04 2001