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Comment Pebble watch is another example (Score 5, Informative) 168

For another example look at the Pebble watch.

Originally wanted $100,000 in funding, wound up getting over $10 million. That changed the size of their problem from making 1000 watches, to making 100,000 watches. So now they had to scale their manufacturing by a factor of 100, which is a totally different set of problems to solve.

There has been a lot of angst (some anger) at the delivery delays, most of the "investors" have been reasonably patient, some have been downright ignorant. One of the most popular forum topics is something like "I funded it on [date], why haven't I got my watch", where [date] was only a small number of days after the kickstarter campaign began, but in reality was when they were at over $5 million going up.

Disclaimer: I'm still waiting (patiently) on my two watches. I should have just ordered black, or changed to black when they made the option available. sigh!

Comment Re:Anybody using Ada? (Score 4, Insightful) 165

Ada is used in lots of places where the application is safety critical or there is a need for high reliability.

It got a lot of bad press, mostly because it originated from a request from the US DoD for a single language to do "all things". It's original MIL-STD designation was 1815 (Ada Lovelace's birth year).

Many aircraft have their flight control systems built in Ada, eg: Boeing 777, Apache Helicopter.

From memory the GPS Block II Satelites, not sure about the Block III.

The original Ada 83 compilers were pretty awful - slow and produced horrible code. But they got way better. Because the language required a "program library" to store information about the compiled units (yes, GNAT showed that it wasn't really necessary), the optimizers in the middle pass and back-end had access to more information than normal, giving scope to some very effective optimizations. I've seen generated code that was as good as the best hand coded assembly - multiple levels of inlining, removal of sub-routine pre and post amble code, delayed branch slot filling, value propogation used to remove implicit and explicit tests etc.

My biggest challenge was always the lack of support for the latest and greatest libraries, eg: X11, MOTIF and their Windows equivalents.

Comment Re:GPS Accuracy (Score 1) 117

I was living in the US at the time when "selective availability" was turned off. This was the deliberate manipulation of the non-military GPS signals to make the position solution less accurate.

I set my laptop up to record and plot my position on the night it was disabled, using a Delorme GPS. The next morning it showed a wide green wandering star-ish shaped track roughly around my house in the early part of the recording, and just a steady green blob for the later hours. I wish I had bothered to be more careful and save the track for historical purposes, but from memory the diameter of the enclosing circle of positions was over 50 meters when SA was on, and only a couple of metres after it had been turned off.

Comment Re:GPS Accuracy (Score 5, Informative) 117

The key thing is that this level of accuracy is not achieved in realtime.

The receivers would be recording more than the information contained in the GPS messages, they would be recording phase and signal strength data for all the satellites in the visible constellation.

Sophisticated post processing software would combine this information across multiple receivers, along with published satellite ephemeris data, to produce an accurate position solution.

Realtime positions cannot be that accurate due to affects like ionospheric refraction etc.

I used to work with a mobile system that recorded the GPS data along with inertial information (at 200Hz) that in realtime gave a solution that was usually accurate to within 30cm, and got to better than 10cm when combined with static ground station data in the post-processing step.

There are systems used in agriculture that are very accurate (10cm-ish) that use differential-GPS in realtime. The trick is your mobile unit has to be in constant communication with the differential ground station. Works ok for tractors, not so well for an aircraft 200-300km away. For differential-GPS to work well both units need to see the same satellites.

Comment Yes it was a software problem, but .... (Score 5, Informative) 603

DISCLAIMER: I hate air travel, but do it most weeks.

I have worked in and around the safety critical software industry for over 20 years. The level of testing and certification that the flight control software for a commercial aircraft is subjected to far exceeds any other industry I'm familiar with. (I'm willing to be educated on nuclear power control software however.)

The actual problem on the Qantas jet was a latent defect that was exposed by a software upgrade to another system. So the bug was there for a long time and I'm sure there are still others waiting to be found. But this doesn't stop me getting on a jet at least twice a week.

As a software professional and nervous flyer, do problems with the aircraft software scare me? No not really. What scares me is the airline outsourcing maintenance to the lowest bidder in China, the pilots not getting enough break time, the idiotic military pilot who ignores airspace protocol, and the lack of english language skills in air traffic controllers and cockpit crew across the region where I fly (English is the international standard for Air Traffic Control).

A good friend is a senior training captain on A330's, and in all the stories he tells software is barely mentioned. What get's priority in the war-stories is the human factors and general equipment issues - dead nav aids, dodgy radios, stupid military pilots. One software story was an Airbus A320 losing 2 1/2 out of 3 screens immediately after takeoff from the old Hong Kong airport. The instructions on how to clear the alarm condition and perform a reset were on the "dead" bottom half of one of the screens.

A great example of software doing it's job is the TCAS system - Traffic Collision Avoidance System ( To quote my friend "If it had lips, he'd kiss it". It's saved his life, and the lives of 100's of passengers, at least twice. Both times through basic human error on the part of the pilot of the other aircraft.

One final thought - on average about 1000 people die in commercial aviation incidents each year world wide (source: . In the USA, over 30,000 people die in vehicle accidents every year.

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