Re: Is it useful to support user level drivers

[Anders Larsen]

"Richard B. Johnson" wrote:
> 
> QNX does not have any difference between user-space and kernel space.
> It's not paged-virtual. It's just one big sheet of address space
> with no memory protection (everything is shared). All procedures
> to be executed are known at compile time.

That's completely, utterly untrue.
QNX does indeed sport paged-virtual memory with memory protection;
(although QNX4 does not support swap).

User-mode interrupts are standard procedure; the deadlock problems
Alan has mentioned do not apply, since any running process is
always resident in memory.
Shared regions have to be explicitly created; access is *not* open
to anybody.

Nothing has to be known at "compile time"; QNX is a full-featured
OS with dynamic loading.

> Therefore, any piece of code can do anything it wants including
> handling hardware directly.

Again not true; only privileged processes can enter kernel mode
to execute port I/O instructions directly.

cheers
Anders
-- 
"In theory there is no difference between theory and practice.
 In practice there is." - Yogi Berra