N900 will not allow USB OTG! - Page 36 - maemo.org

Frank Banul | # 351 | 2009-09-28, 14:34 | Report

USB OTG consists of 5 signals in the connector, 2 power, 2 data and one ID to indicate host or device. It would be as simple as removing this ID signal and leaving the other 4 signals and then hard coding the USB transceiver to be device only. So the OMAP3430 supports OTG, it's just never being told to go into host mode.

Originally Posted by Mandor View Post

How can Nokia modify the OMAP3430 to take that feature out of the N900 ? Is it something easy to do ? I mean like not plugging the "thing" that support USB On-The-Go.

Frank

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qole | # 352 | 2009-09-28, 16:41 | Report

Frank: What is "hard coding" the USB transceiver to be device only? Is that user-accessible software (even the kernel is user-accessible), or is it "hard wiring," either with physical wires or firmware that can't be reached by the user?

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Frank Banul | # 353 | 2009-09-28, 16:50 | Report

It could be either. The signal could be physically tied high to indicate a device. I would be inclined to do it via software myself to give the flexibility to change later without changing the hardware.

I have to admit that I've only forced host mode via software, so I'm not entirely sure that device mode can be forced via software but I think it's a safe assumption.

Originally Posted by qole View Post

Frank: What is "hard coding" the USB transceiver to be device only? Is that user-accessible software (even the kernel is user-accessible), or is it "hard wiring," either with physical wires or firmware that can't be reached by the user?

Frank

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Mandor | # 354 | 2009-09-28, 23:47 | Report

@qole :

Thank you for the translation, that is what I meant.

@Frank :

Correct me if I am wrong but from what I understand (and again you should take that lightly) OMAP3430 does support charging through the USB port and does support USB OTG. So I really don't understand when I read Nokia had to sacrifice USB OTG in order to get USB charging. Both are there anyway, don't they ?

The Pandora, for example (is it a good example ?) does support USB OTG, host and charging (through USB and dedicated power supply).

Again, I am just trying to understand and educate myself.

allnameswereout | # 355 | 2009-09-29, 00:14 | Report

Originally Posted by

Yes, through the mini-AB OTG port

The USB specification does not allow microUSB to be used for both charging and OTG. Read the PDFs linked to in this thread, and the comments on these PDFs. Please read the thread before replying!

I don't understand why there is still discussion to try to enable it in software. Clearly, it does not work to enable it via procfs (or sysctl). Doesn't that automatically mean you're gonna resort to a hardware hack? While OS is running how can you go more lower level than kernel? I think, we'll have to see about that 5th ID pin.

quingu | # 356 | 2009-09-29, 08:48 | Report

Originally Posted by Mandor View Post

@qole :
The Pandora, for example (is it a good example ?) does support USB OTG, host and charging (through USB and dedicated power supply).

Well, the pandora does have two seperate usb port - one fullsize type A, and the mini otg port. Yet the developers said that one could use the otg port as a host, iirc.

Also, the pandora's otg port is exclusively usb1.1, while the fullsize port is exclusively usb2.0. Not sure what witchcraft they did to those ports.

TA-t3 | # 357 | 2009-09-29, 09:19 | Report

Originally Posted by quingu View Post

Also, the pandora's otg port is exclusively usb1.1, while the fullsize port is exclusively usb2.0. Not sure what witchcraft they did to those ports.

No, that's not correct. Both ports are USB2.0, but the fullsize port (the host port, USB A connector) is HS (High Speed) only, it cannot support the other two (lower) speeds. On the other hand it can provide 500mA.

The small-connector OTG port (USB mini-AB) is also USB2.0, but it can support all three speeds. It can also be configured to be host port. But this port cannot provide more than 100mA.

Edit: Found a link that describes it better than I can: http://pandorawiki.org/USB_reference

Last edited by TA-t3; 2009-09-29 at 09:28.

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quingu | # 358 | 2009-09-29, 09:40 | Report

I stand corrected. Thanks TA-t3.

attila77 | # 359 | 2009-09-29, 09:54 | Report

Originally Posted by Mandor View Post

The Pandora, for example (is it a good example ?) does support USB OTG, host and charging (through USB and dedicated power supply).

The Pandora is sporting an uncertifiable USB configuration. It doesn't mean it doesn't work, but is (strictly speaking) against the (sometimes brain damaged) procedures and specs. But the USB certified or USB OTG sticker means a lot less for the Pandora folks than it does for Nokia.

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TA-t3 | # 360 | 2009-09-29, 10:36 | Report

Note that the N900 uses micro-USB, the Pandora mini-USB. The rules are different for the former and that's what causes this particular problem.

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