Lpc2000

At 11:47 AM 4/20/06 +0200, 42Bastian Schick wrote:
>Robert Adsett schrieb:
>
>I jump in late, so sorry if I repeat an arguement:

Just as Jaya and I were winding down to a conclusion :)


> > 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.

I suggested that once as a possible advantage.  Jaya assured me that the 
interrupt disable/restore was exposed as a function across the barrier in 
his implementation.  That would rather negate the advantage.

I can see that (restricting the ability to disable interrupts) as an 
advantage, especially for larger systems.  When I asked the question 
originally it hadn't occurred to me to only disable interrupts in system 
mode.  For most of the stuff I do I don't see it being worth the extra 
trouble but that does make the distinction useful for a wider variety of 
projects.  Of course once you had it set up like that for one project it 
would be easy to carry across to smaller projects at little or no cost.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/