Fwd: Adding a system management MPU

Wolfgang Spraul wolfgang at openmoko.com
Thu Mar 20 07:54:06 CET 2008


fyi

Begin forwarded message:

> From: Milosch Meriac <meriac at openmoko.org>
> Date: March 19, 2008 4:51:46 AM GMT+08:00
> Subject: Re: Adding a system management MPU
>
> Hi Andy,
>
> Andy Green wrote:
>> Particularly as we established we are getting rid of U-Boot and  
>> have a
>> minimal bootloader, if we wake the CPU it means waking into Linux one
>> way or another before anything complicated gets done.  We can use  
>> this
>> MPU to manage power and button/touchscreen/connector events, motion
>> sensors, battery HDQ, PMU, LEDs in a central, consistent and complete
>> way without needing to bring the CPU into it and without any dead  
>> time
>> while we wake the CPU.
>> Something along these lines (6.8mm x 6.8mm footprint) $3.10 / 100
>> http://focus.ti.com/docs/prod/folders/print/msp430f2272.html
>> http://www.ti.com/lit/gpn/msp430f2272
>
> 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.
> I attached all user peripherals to it: It controls the charging  
> current by reading the USB id pin, controls the touch screen, wakes  
> the CPU, controls the PMU and powersave modes,  handles the  
> vibration motor, measures voltages and currents, detects swapped SD  
> cards, handles the cheaper accelerometer (analog interface only) and  
> scans our touch screen. This allowed me in turn to put the CPU even  
> into deep sleep and let the MSP430 decide when to wake it up (based  
> on accelerometer readings etc.).
> 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.
>
> Warmest regards,
> --
> Milosch

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