Чтобы не гадать на кофейной гуще я поискал конкретные слова по теме, в том числе нокиевцев.
http://lists.maemo.org/pipermail/maemo- … 20830.html
> The N900 comes without USB host mode. When I asked I was told that the
> limitation comes at hardware level.
I can confirm this. The most reasonable setup would have been to provide
the A connector, but only gadget mode working forthe sales release, then
in a SW update to provide full spectrum support.
Then enters the USB certification with all its mass of quite often
bizantine, obsolete and plain braindead requirements.
One of them being that the certification with A connector can be passed
only if full functionality is provided by the SW.
In this case I propose that complaints are directed to the USB
consortium. I have really come to doubt that it's actually protecting
the consumers' interests in nowadays scenario.
> The reason for this decision was the complexity of providing support
> for charging, PC connectivity and USB OTG efficiently through the same
> Micro USB port within the project deadlines.
Add to that several HW bugs that were discovered during the development
and needed workarounds.
> We needed to make choices and the decision was to sacrify USB OTG and
> concentrate on the essential use cases of charging and connecting to
> the PC, bringing the N900 to the market in its due time.
Although noone really liked the choice we had to make. We do use our
products and as consumers we are aware of the limitations sometimes we
have to apply.
http://talk.maemo.org/showthread.php?p= … post643577
Then, as quite clearly stated here, Nokia wasn't able to finish the whole complex driver zoo for OTG, charging, etc pp just in time and so had issues with usb.org cert authorities to the point where they either
a) could ship a device with option to implement full OTG later, but lacking USB certification, which would create all sorts of secondary problems (Microsoft not signing the driver, China and EU feeling pissed by Nokia not adhering to their rules for mobile devices&chargers, dunno what else), or
b) replace the micro-AB receptacle by a micro-B type, and thus circumvent all the OTG trouble, as B type per definitionem does NOT support OTG (and the ID pin is all about OTG and detecting A-plugs, and nothing else, btw) - get cert from usb.org easily, and ship several months earlier.]]
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.
The USB port with embedded host mode could not be certified, as the OTG drivers were not ready. (see  last block).
This lead to the the micro-AB USB connector being replaced by a micro-B, and the host functionality being officially removed short time before launch.
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.
То есть, если я всё правильно понял, проблема была не в том, что OTG + зарядка не проходят под стандарт. Проблема в том, что Nokia не успевала довести OTG-драйвера до полностью работающего состояния, а сертификация USB требует, чтобы софт был рабочий и поддерживающий все требуемые функции на 100%. Включая ненужные и устаревшие. А забить на USB-сертификацию было нельзя, так как это привело бы к куче других проблем, таких как невозможность подписать драйвера для ПК и проч.
И в первоначальных планах, как я понял, было доделать OTG после выпуска устройства и добавить в очередной прошивке. Однако, Nokia как всегда забила, и теперь этим занимаются волонтёры.
Так что насчёт отсутствия пяти вольт в разъёме это я похоже сам придумал
N̶8̶0̶0̶ + N̶8̶1̶0̶ + N̶9̶0̶0̶ + N̶9̶5̶0̶ + N̶9̶ ̶C̶y̶a̶n̶ + N̶9̶ ̶B̶l̶a̶c̶k̶