Messages in this thread |  | | | Date | Thu, 6 Jan 2000 23:55:26 +0200 | | From | Matti Aarnio <> | | Subject | Re: time_t size: The year 2038 bug? |
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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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