PDP-11 still supported - thanks for the info

Posted Jul 15, 2024 20:02 UTC (Mon) by jjs (guest, #10315)
In reply to: PDP-11 still supported by farnz
Parent article: The 6.10 kernel has been released

thanks to both @paulj and @farnz for the info. As I say in another comment, been away from that realm for a while, but not surprised the problem hasn't gone away. It's a hard problem to solve. I can see why a nuclear power company would do that - as you say, recertification can be difficult, but things change. I would think the less changes made, the easier to recertify. Easier to recertify the changes on the old box than certify a new box & software.

Recertification of power plant code

Posted Jul 16, 2024 9:35 UTC (Tue) by farnz (subscriber, #17727) [Link] (2 responses)

They want to stick to PAL11-R for exactly the reason you suggested; when they recertify, they look at the difference between the last certified system, and the latest certified system. They only need demonstrate that the changes are safe to recertify - so the smaller the changes, the easier it becomes.

So, switching from a PDP-11 to a Cortex-M4F with more compute and I/O than the PDP-11 is a huge deal; everything changes, so everything has to be recertified, from hardware upwards. Sticking on a PDP-11 and switching from PAL11-R to MACRO11 is also a big deal, because all the software needs rechecking, and to be able to recheck at source level (not machine code), they'd have to get MACRO11 qualified as producing predictable output, where PAL11-R is already a qualified tool. Similar would apply to using a higher level language like BLISS or C - you have to qualify the toolchain first, and that's expensive.

And this is all sufficiently expensive that it's cheaper to pay for people to pick up a legacy assembly language and just update the legacy codebase for new regulatory and safety requirements (e.g. they had a flurry of activity after Fukushima) than it is to update to a newer language, let alone pay the cost of migrating to new hardware.

Recertification of power plant code

Posted Jul 18, 2024 4:29 UTC (Thu) by raven667 (subscriber, #5198) [Link] (1 responses)

Honestly, this is probably as it should be, if the machine is still capable of doing the job, because the job hasn't significantly changed, then why should the whole thing need to be upended and rebuilt due to software fashion.

Recertification of power plant code

Posted Jul 18, 2024 7:28 UTC (Thu) by farnz (subscriber, #17727) [Link]

A shift to MACRO11 instead of PAL11-R isn't a big change - all of the existing source would assemble as-is, and the new features of MACRO11 (which are all over 40 years old) would help when you're doing maintenance on the changes made to the system.

And the reason for stability is not that the job hasn't significantly changed - it has - it's that if you want the benefits of the modern control system, you have to pay for it. However, nuclear power plants are regulated such that you can't just say "there's a new system - pay to install it, because we're not supporting the old one" - if the company wants to upgrade you to the newer 68k based control system, they have to pay the cost of replacement.