and the kernel is written with pre-emptive concurrency in mind (rather than, say, retrofitting

it all). That extends to the drivers and most platform-specific kernel code (except where someone slipped up,

which is rare). Even on things that are currently uniprocessor, the discipline is to write the

mutual exclusion code as required. Cache control is less well-developed,

since most platforms so far have offered some adequate form of coherency, but

explicit cache flushing and invalidation is missing from some x86 drivers, because

the architecture did the work, so that DOS would run. In practice, most embedded platforms

have had custom SoC devices, or different devices from x86 at any rate,

so the cache flushing was included when a new driver

was written (once we understood the problem). Unfortunately, it was done

using different primitives, or at least primitive names, for different architectures.