11 ms·
Not an airplane programmer, but I seem to remember that the literature says that it's not generally a cost-effective way of finding bugs. In particular, you mul
by CHY872 11y ago
Not an airplane programmer, but I seem to remember that the literature says that it's not generally a cost-effective way of finding bugs. In particular, you multiply the cost of development by (say) 3x (which is fine, on its own) but also the places where bugs are inserted are typically the hard parts; so you don't reduce the number of bugs as much as you'd like; it can easily be more cost effective to invest the few million in static analysis etc.
As much as we'd like plane manufacturers to test things to death, it'd become too expensive too quickly. For all we know, this software could be written by a contractor, or the firmware for a third party part.
As far as I know, N-version programming was effective when software systems were small (shuttle ran on 50k lines of code) and where poring over every single line was possible, because the hard part was coming up with the spec.
Nowadays a big plane like the A380 might be expected to have 100M lines of code in its subsystems, and it's simply too expensive.
- hello_there 11y ago> Nowadays a big plane like the A380 might be expected to have 100M lines of code in its subsystems, Why does an airplane require 100M lines of code?
- mschuster91 11y agoLinux kernel alone comes in at 15m SLOC. Now add an userland subsystem and you're at 20-30M just for one device. Multiply by all the little and big subsystems, the embedded chips, in-flight entertainment, network gear... 100m SLOC is too low, I think.
- CHY872 11y agoErm, the article I got my numbers from is: http://www.aerospacelab-journal.org/sites/www.aerospacelab-journal.org/files/AL04-10_1.pdf http://www.aerospacelab-journal.org/sites/www.aerospacelab-j... where it states that the airbus A380 has more than 100 million lines of code in its avionics systems.
- georgerobinson 11y agoSorry if this is incredibly ignorant, but I can't believe flight control systems are running Linux? Do these systems not have hard real-time requirements about the execution time and periodicity of tasks which can't be guaranteed by the time-sharing scheduling algorithms in Linux?
- komaromy 11y agoThere are several real-time Linux variants.
- jacquesm 11y agoThere are - to my knowledge, feel free to correct me - no real time linux versions (or even any version of linux) that are currently certified for avionics (DO-178B certification is required for that, there are multiple levels and I don't know of any linux distro (or just the kernel) with that certification).
- komaromy 11y agoAvionics certifications are well past the extent of my knowledge and I will gladly accept your point. I was generally addressing the idea that the need for preemptive scheduling precludes the use of a Linux-like kernel.
- anderspitman 11y agoI've never heard of anyone getting Linux running under hard real time constraints. You can get it pretty good (excellent for real time audio, for example), but can never be 100% sure you're going to meet the deadline. The people I've talked to who tried said by the time you strip out enough of the kernel to approach hard real time, you've lost enough of the advantage of using Linux that you may as well switch to an RTOS.
- jacquesm 11y ago
- Dylan16807 11y ago3/4 of that 15M is drivers and filesystems you won't be using, and this is not including the entertainment systems. They should be able to keep it under 10M lines pretty easily if they actually cared about bloat.
- CHY872 11y agoA complicating factor is that you really should include your compiler as part of your codebase (if you're doing lots of formal method work, you will usually do it on the source code, and the compiler can invalidate all of the guarantees you carefully program in), and this will be millions of lines of code (where you can't simply factor a tonne out). Think GCC 5 is about 15 million or so now.
- oldmanjay 11y agoit's always easy when you're not the one making the changes on the system you don't understand. is there a name for that? I feel like it's a common enough thing people do that it should have a catchy name.
- Dylan16807 11y agoEh. To say that something that used to be mechanical should be possible with a mere few million lines of code seems pretty obvious to me. Or compare to the Apollo missions and the space shuttle being well under a million. I'm not saying that it would be easy to redo the entire system from scratch now, I'm just saying that if it was a design goal from the start it wouldn't have been very onerous.
- deleted 11y ago[deleted]
- icegreentea 11y agoBecause each discrete component that you can eliminate (and replace with code) is a weight saving. Because once you tip over a point in complexity, you just keep adding more code to guard against more edge cases - edge cases you can't avoid because they involve crashing into mountains. Because you want to offload as much possible effort from the cockpit crew, while still allowing them full control over the automated feature All of these things just add more and more code.