> It is perfectly possible to deal with hardware in managed languages.

Perhaps we're using the words in different ways. What I mean is: in order to interact with something, it must either be done directly or through abstraction. If abstraction is used, it must be realized without itself. A language such as Java or C#, at least for performance, must expose some things on a lower level that the runtime normally abstracts away. (Or, say, the OS memory manager can't use virtual memory before it enables virtual memory.) Technically, the lower level could be programmed with a dialect of Java/C# or something like that, or there may be another level of abstraction that hides the details (a compiler generating code in the background, for example). But something has to be the first step at the bottom.

> Yes, IPC is context switching.

(Considering the diversity of how OSes approach context switches/IPC, I use "context switch" to mean "CPU mode/address space switch", more or less.)

Usually, IPC is context switching and overhead. seL4's IPC has overhead involved with scheduling, threads, and message buffering. My design isolates the context switching, which is common to all IPC designs.

> Timer interrupts can cause extra context switches.

I don't see what your point is. I assure you that my system is not uniquely fragile to timer interrupts.

> It's trivial, except for the little problem that your userspace program can be killed and then you have no scheduler.

Then don't let the scheduler be killed. What is the difference between a privileged userspace program and a kernelspace program? Isn't that what microkernels demonstrate? Again, this has been done before.

> Ok. If you want to use a different description of the term syscall than is common then that's fine but you should define that up front. Your definition of a syscall simply does not match mine.

It wasn't quite a definition, though I did write poorly. In the abstract, a syscall can be seen as a message. If IPC ("to a process") is done by putting some data somewhere, setting a few registers to special values, and executing a magic syscall instruction, then a normal syscall can be considered IPC "to the kernel".