N900 Hardware USB

The USB connector on the n900 is a micro-b connector, as required in european and chinese markets, under the new scheme to make all phone charger sockets identical.

Contents

USB socket

USB implementation

The n900 seems initially to have been designed to be capable of acting as a USB host, or implementing OSG mode. This would have allowed keyboards, mice, and other peripherals to be plugged in.

This was changed relatively soon before release, and the host functionality was officialy removed - in order to comply with the USB standard - it could not get certification as a standard USB port with host mode, and the micro-b connector.

Lacking certification would have a large number of issues, from some operating systems requiring certification before allowing drivers to be distributed, to legal compliance with the USB charger specs - it would technically not be a USB port.

The Chips

There are four chips involved in the USB subsystem.

SoC

USB battery charger

The bq24150 charger from TI is quite a flexible charger.

USB Phy

The NXP isp1707 is used as the USB PHY chip. [1]. This rights to this part have been bought by ST-Ericson and some information is available in a brief marketing sheet.

There is no published datasheet for this chip. It may be available under another name.

The device would normally be switched between host and device mode using the ID pin. This however is not connected externally.

Initially it was claimed that this made USB host mode impossible.

This however seems to be incorrect - it seems on a reading of similar device datasheets that yes, the ID pin is used on hardware that supports it to switch between host and device mode.

But, importantly, the ID pin does nothing directly to the state of the chip. It simply informs the CPU of the state of the ID pin, and leaves the driver to properly configure the chip.

So, if the kernel can be altered to ignore this pin - which should be trivial if there is host mode support for the chip in the kernel - then host mode works.

The current understanding by several people who are working on USB host mode is:

The USB port can supply power - at least 200mA. This is plenty for many devices - mice and keyboards.

It seems likely that a relatively simple kernel change should enable USB hostmode - http://focus.ti.com/lit/ug/spruf98d/spruf98d.pdf - search for FORCE_HOST - there may well be other cleaner solutions.

A possibly related errata is detailed at 3.1.3 in this document - this, and other erratas may or may not cause issues with implementing host mode.

USB socket

It seems that there is a USB socket hardware issue on some N900 ...

May this depends on the build date, can you help and report details on your broken device :


No reason to panic most users are not affected and it could be trivial to prevent or repair once investigated by some diy hackers...

what to do ?

Please fill ( template : nickname : build date ; SN  ; contact url or email ; notes ) , also tell hw version (" sysinfo-tool -g /device/hw-version" )

Also answers polls :


Solution

Misc