Lpc2000

Jaya,

Robert is not incorrect. 

The fact the LPC2k has different operating modes does not mean it 
has the capability of implementing a privileged mode operating 
system. Hence your comment "If this were true, the notion of 
privilege or levels of privilege in operating systems would 
meaningless" is itself meaningless.

The purpose of such operating systems is to have fortress-like walls 
around the operating system/kernel facilities, memory and I/O space. 
These walls are built using privileged processor modes and some form 
of memory protection. The memory protection bit is absent on the 
LPC2k.

The purpose of mechanisms like software interrupts is to provide a 
controlled gateway through these walls. If these walls don't exist 
(and they don't on the LPC2k, as it has no memory protection 
mechanism), any application can simply bypass the gateway and wreck 
havoc with the system. In other words, your carefully constructed 
gateway has no functional use whatsoever (as Robert has pointed out).

The software interrupt mechanism has no protection in itself: it is 
simply a mechanism to gain access through a protected barrier.

You are of course quite free to implement whatever modes and 
features you want. However, if you think that by implementing 
software interrupts and making use of user mode somehow offers you 
any degree of protection, you are deluding yourself (and from what 
you say, your clients). It simply isn't the case.

If I've stated anything factually incorrect above, I'm happy to 
correct it.

Hopefully though, this will clarify matters, and prevent yet another 
interminable discussion.

Brendan

--- In lpc2000@yahoogroups.com, "jayasooriah" <jayasooriah@...> 
wrote:
>
> Robert,
> 
> Given my aim is to present an alternative view, but not to impose 
this
> on anyone who does not appreciate its merits, I like pointing out 
only
> what I believe has been grossly mistated or incorrect:
> 
> --- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@> >
> Nonsense.  If the user application hangs up the fact that the user
> code is 
> > in user mode but the kernal in system mode won't make recovery
> easier or 
> > harder.
> 
> [example deleted]
> 
> If this were true, the notion of privilege or levels of privilage 
in
> operating systems would meaningless.
> 
> > There is zero extra protection available by placing the kernal in
> system 
> > mode and the application in user mode.
> 
> You may not see them, but I do and we just have to agree to 
disagree.
> 
> [I tend to work towards clients requirements and not redefine them.
> When they say they want to do this, I just show them how to.]
> 
> Cheers,
> 
> Jaya
>