Via HN, the tale of chasing down a hardware bug in an ARM CPU.

Andrew_Reid · February 18, 2018, 11:03pm

ARM does not manufacture CPUs itself, but licenses out the designs, which are fleshed out into products, fabbed and sold by the licensees.

This particular ARM chip had an issue with “atomic” memory operations (operations that take place in a way which is immune to interference from other threads), turns out these operations bypassed the CPU cache, causing nonsensical results in some cases.

The bug was found and tracked down by the authors of the FreeRTOS operating system.

EdS · February 19, 2018, 5:49am

(ARM has a couple of models: it licences its own designs, and it also issues architectural licenses where others do the designs, which must pass a compliance suite. In this case it may be that NXP were the designers responsible for the bug. )

EdS · February 19, 2018, 6:10am

(Ref: https://news.ycombinator.com/item?id=16408030
Not that there’s yet much of a discussion. )