From Roger Ford's 'Informed Sources' e-preview:
Engineers commissioning the new generation of software-enabled trains are
facing the problem that pretty well every system, and even sub-system, on
their train is computer controlled with its own software. This also has to
interface with the train’s third party software based systems.
For example, during a recent run in a Great Western Railway Class 800 the
Universal Access Toilet was all lit up, but the door had lost power and
wouldn’t lock. When I reported this failure to a member of the on-board
staff, she replied that it was a common issue and the toilet needed
Lest you think that this is just a case of hide-bound traction and rolling
stock engineers unable to cope with new fangled technology, in the column I
quote the Lockheed Martin F-35 fighter comparison.
Its software has been released in ‘blocks’. The latest block, which will
meet the full military specification, took over 30 iterations of the
software to implement. According to Arriva Rail London, the software for
the Bombardier Class 710 Aventra, which has yet to enter service, has
reached Version 27.