Fwd: Adding a system management MPU

Wolfgang Spraul wolfgang at openmoko.com
Thu Mar 20 07:54:33 CET 2008


fyi

Begin forwarded message:

> From: Andy Green <andy at openmoko.com>
> Date: March 19, 2008 5:09:04 AM GMT+08:00
> Subject: Re: Adding a system management MPU
>
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> Somebody in the thread at some point said:
>
> Hi Milosch -
>
>>> way or another before anything complicated gets done.  We can use  
>>> this
>>> MPU to manage power and button/touchscreen/connector events, motion
>
>> Funnily I chose a very similar chip for my Ebook Reader design - the
>> MSP420F233 (dirt cheap and a supports lot of peripherals).  
>> Basically it
>> allowed me to stick to a cheap PMU.
>
> Sounds like we both found a use for our exposure to the Xbox system
> controller after some time :-)
>
>> My main CPU (iMX31) talks to the MSP via as SPI master - the MSP  
>> toggles
>> an IRQ line to request a status poll by the main CPU. The bluetooth
>> module is shared by iMX and MSP - which allows great debugging and
>> debricking action over Bluetooth/RFCOMM serial interface without  
>> opening
>> the device at all - you are also able to see even early kernel boot
>> messages over Bluetooth or reset the CPU over bluetooth. The MSP also
>> handles the timer for alarm etc.
>
> That sounds very cool in your design.
>
> There is a plan to basically put the debug board FTDI chip on the
> mainboard for JTAG / debrick purposes, along with a micro USB conn  
> that
> isn't accessible without opening the case.  So we discard the debug
> board as a "product" and all phones expose a "USB UART" console and  
> JTAG
> if you want it.
>
> If we allow "system MPU" reprogramming and therefore bricking (which  
> we
> should) it too can be debricked over JTAG, so having a physical  
> debrick
> / hacking port of last resort is still valuable.
>
> - -Andy
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