On Thu, Jan 06, 2000 at 12:06:40PM -0800, David Schwartz wrote:
...
> I realize that this is common sense, but it's just not true.
> The defintion of "the job" is depedent upon what chips are available.
> When the scope of the embedded system is defined, it's based upon
> the current level of technology.
>
> Why did the Hubble, and embedded system, just get upgraded to
> a 486-50? Obviously the system that was there before did the job, right?
Aside of getting more of house-keeping data processing,
and memory storage capacity ? (Than with the original
16 bit 1172A processor.)
> No, what happened was the availability of more powerful embedded
> processors changed the _scope_ of what the job was. This is what has
> _always_ happened.
The case with HUBBLE is *very* special, even though it is
(sort of) embedded system. NASA is flying Linux on space-
missions where it 1) isn't life critical system 2) where the
computing hardware is in human rated environment.
(Note: I didn't say *mission critical* -- mission (science)
goals may well depend on functionality of the Linux based
laptop, but that is "just" a big embarrasment, not dead
astronauts.)
The HUBBLE is *not* Human rated. In fact it flies thru so
called South Atlantic Magnetic Anomaly at every orbit -- every
about 1.5 hours. (Well, not *every* orbit, only every 3rd-4th,
or so..) That area in near-earth space happens to be low-lying
extension of Van Allen radiation belts around our planet.
(The service missions don't have the astronauts doing EVA while
the flightpath enters that area of space.)
So why 486-50 ? It is available in radiation hardened model.
(I didn't know that - but its been a few years since I checked
what is available in that esoteric hardware field.)
A friend of mine used to be writing software for embedded systems.
He said roughly: Embedded software is where PROM change needs
digger crew to get to to box buried under a busy street. (If not
a cable-ship to drag it out from the bottom of an ocean ... or
need a shuttle mission worth around USD 1 billion..)
Those cadgets below the streets and in the ocean do tend stay in
service for *long* times. Tens of years, very least. Mainly
because the installation costs are so high... (The cadget costs
next to nothing compared to the work.)
....
> DS
/Matti Aarnio
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