N900 Hardware Power management
The power managment on the n900 is very complex, and involves a large number of interacting systems.
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Hardware
There are four chips involved in the USB subsystem.
SoC
The System-on-a-chip is the main processor on the n900. This is the TI omap3430
Gaia
The TWL4030 is a TI companion chip to the SoC.
USB battery charger
The bq24150 charger from TI is a flexible charger. It, along with the PHY chip - support charging without the intervention of the SoC when the system is charging from a completely dead battery. The PHY chip detects a charger (shorted D+ and D- pins) and the charger uses this information to charge more rapidly.
It also features reverse boost mode - which enables power to be supplied to a USB device connected to the N900. (up to a limit of 200mA)
For more information see N900 Hardware Battery Charger