Lpc2000

--- In lpc2000@yahoogroups.com, 42Bastian Schick <bastian42@...> wrote:
> > The question is: what extra advantage running in user mode and
making calls 
> > to a system mode kernal provides over an application running in
system mode 
> > making calls to a system mode kernal?
> 
> Even if there is no MMU/MPU which restricts access to memory, one vital
> resource can be restricted: Interrupts.
> 
> In USR mode, you cannot modify the interrupt-bits whereas in SYS mode
> you can.
> 
> Means, running tasks in USR mode lets the OS control the disabling of
> interrupts.

Thanks Bastian for pointing out Robert's questions I missed in my most
recent response.

My understanding of Robert's position (apologies if I misunderstood)
is that because there are other ways a rogue task running in user mode
can compromise the system why bother running any in user mode at all.

Given if one uses the SWI interface, it comes at no cost, I prefer to
question why not.

I can see why some chose to run all tasks in user mode to harness not
only the direct privilege differences you point out, but also ripple
down effects onto other things for control for coordination purposes.

Accepting embedded ARM users in general have different requirements,
my personal experience has been that that LPC users appear to have
somewhat different requirements compared to users of other variants. 
Especially on on matters related to security, protection, and maybe
even watchdog requirements.

Jaya