I worked with an embedded phone OS once where the entire realtime OS ran as a single task in an L4 microkernel. This was to allow the realtime OS to run in a d

I worked with an embedded phone OS once where the entire realtime OS ran as a single task in an L4 microkernel. This was to allow the realtime OS to run in a demand paged environment: if the OS accessed an address from the area defined as 'rom', L4 would allocate a page of RAM and populate it from flash. The whole purpose of this was solely to allow them to use a cheap NAND flash chip rather than a NOR flash chip (NOR flash can be memory mapped, NAND can't). That was the only thing they used L4 for. Everything else operating-system-wise was done by the embedded OS, device drivers and all. Surprisingly, it actually worked. (The rest of the OS was a horrible trainwreck, but not this bit.)