LED notification

[Kishore]

On Friday 17 Oct 2008 8:16:10 pm Michael wrote:
> On 16/10/08 16:52:10, Andy Green wrote:
> > Somebody in the thread at some point said:
> > | (The first message I sent does not seem to have arrived)
> > |
> > | On 12/10/08 18:00:55, Andy Green wrote:
> > |> Yes always-on MPU can deliver consistent power behaviours we can't
> >
> > do
> >
> > |> in
> > |> our current way of relying on PMU.  You would basically make the
> >
> > PMU
> >
> > |> a
> > |> slave of the MPU.  Stuff like debricking scheme for a programmable
> > |> and
> > |> so brickable MPU that controls the PMU... needs careful thought.
> > |>
> > |> -Andy
> > |
> > | That shouldn't be a problem, because microcontrollers support in
> > | circuit serial programming, so just make sure we can get to those
> >
> > pins
> >
> > | and have a doc that specifies the programming protocol for the
> >
> > brave.
> >
> > The issue is that if we allow user-updateable MPU, it can always be
> > bricked.  So for example we put out a new package with some MPU
> > update
> > that is broken, suddenly many devices could be bricked before we pull
> > it.  We definitely need some credible sequence of actions for the
> > end-user that can unbrick the devices.  Just telling him where some
> > pins
> > are doesn't really cut it.
> >
> > If the MPU is master of the CPU, then when it is bricked a lot of
> > assets
> > we might otherwise call on are unavailable.  So it needs thinking
> > through being aware of specific capabilities of the MPU.
>
> Should have mentioned that I have flashed microcontrollers for various
> projects that I am doing, so this was just meant for people who are
> used to this sort of thing rather than end users. I think you would
> probably want to leave MCU updates to the distributors or people who
> have done this sort of thing before and I suppose you would need a nano
> boot loader if you wanted to flash the MCU from user space (if
> microcontrollers that small will allow you to rewrite the flash from
> code).

Indeed this is the method we follow for microcontrollers that may need firmware 
upgrade after deployment. the controller itself has a small boot loader that 
can only be modified with a hardware programmer. This basic boot loader can be 
used to flash the firmware that acts as the "Linux" boot loader.
Of course, this may require that the USB port be multiplexed so the 
microcontroller is connected to it at boot and the main controller takes over 
later.
-- 
Cheers!
Kishore