Did you do anything to feed power into the 770?

The USB host port on a powered hub is not supposed to actually provide power to the computer that you're plugging it into - it's supposed to _get_ power from that port. Normally, the power that goes into the hub is only used to power the gadgets you plug into the hub, not the hub itself.

If your hub provides power upstream to the 770 without something like a three headed cable - that is, if just a gender changer works - then your USB hub is totally violating the USB spec. It's convenient when they do that, since it makes it easier to use them on the 770. However, don't be surprised if most of the hubs _don't_ work.

Also, just to clarify a bit, the 770's USB chipset is designed to work as a host or a device. However, if you (where by "you" I mean an electronic engineer building a device using the chip) want it to be a host, you are supposed to do two things:
1. Include a 5v power supply in your design.
2. Use a different connector. There's a USB standard connector that works with the standard cables that the 770 uses now, _or_ a cable that connects it to other USB _devices_.

USB host mode on the 770 is there because the component that Nokia chose to use happened, conveniently, to have features that they didn't really intend to use. They were cheapskates and skipped those components.

Do you see a blue USB icon in the top bar when you plug in a USB device? You may not have power feeding both ways up the line. The 5V line feeds both into the keyboard AND the 770. Weird, yes. Off standard, yes. But it's how it works.

I've got to disagree with all the folks that are saying Nokia did something wrong. Actually I think they set up the USB perfectly logically. This device is a compromise... give enough hackability to get the gadgetheads to participate but make it a mass market device.

The USB port is designed to be a mass storage slave so the consumer can move big files to the RSMMC. If the USB chipset were internally powered off the 770 battery then you would only be able to transfer files when the 770 was charged and you run the risk of draining the 770 battery in the middle of transferring a huge file and corrupting your card. It would be very stupid to make the USB chipset internally powered. It would only shorten battery life and add no functionality for the vast majority of folks who will use this device.

I don't know if the USB host capability was an accident or a little bonus thrown in for the hackers but it is definitely not a design mistake.

David

My USB hub does this too and discovered this power back-feed by noticing that the fan on my video card would keep spinning even when my computer was turned off ... and unplugged!
I bought a USB gender changer to check if I could use this "feature" to my advantage. I haven't tried it yet but I did confirm that the voltage lines on the connector pinout are the same as when the cable is connected to the computer when you are operating the 770 in the normal slave mode. Not sure about the data lines ...

Update: I tried it out tonight and mounting a USB dongle works like a charm! :]
The exact model of USB hub that I have comes from the APC USB 2.0 Starter Kit (UPC 731304238706) that I bought at CostCo. Plug in the cable where the host computer normally goes. Plug in a USB gender changer into that. Plug in the cable that come with your 770 into that and you are all set. No soldering/cutting/splicing needed. Just a $20 hub and a $5 gender changer.

It's not a matter of either or- the idea is that the 770 could provide power to the USB chipset when it chose to, ie: when it was in USB host mode. It could trivially turn this power off when it was a USB device.

Are you certain that the 770 will currently work as a USB flash reader when its battery is dead? I'm fairly certain that it requires battery power to operate. The Linux kernel sits in the middle of everything - the USB interface talks to the processor, which then talks to the RS-MMC slot. No kernel == no RS-MMC reading. No battery == no kernel.

Turns out my problem lies in the fact that I'm splicing power off the Nokia AC-4E adaptor to feed into a 5VDC regulator to serve as the USB power. The Nokia AC-4E adaptor doesn't supply a consistent voltage when plugged into both the Nokia and my kludged on 5V regulator ( LT1521-5). In particular, the adaptor's output voltage alternates between 6.3VDC and 4.5VDC in a square wave pattern. The duty cycle of the square wave depends on how much power is being drawn. The problem is then that 4.5VDC is insufficient for USB. So, the easiest solution I can think of is to replace the Nokia adaptor with a beefier 5VDC adaptor. My question now is, what is the maximum input voltage from the charging adaptor the Nokia 770 can handle? Note that almost all AC->DC converters actually output a higher voltage than indicated on the packaging. Thanks. -TM-

Please don't try connecting the 770 to a 5V (Or another voltage) supply directly. The 770 depends on having its supply current-limited at somewhere around 500 mA. This is my experience anyway, and if you fry your tablet you get to keep the charred remains :-) The third-party charger I bought puts out 6V current-limited at 500 mA and seems to work fine. It never goes above 6V and utilizes a switchmode circuit to allow you to plug it into 120VAC or a cigarette lighter receptacle.

Larry

I want to relate to you my experience with USB host mode, ask for recommendations on the most convenient USB keyboards you've found, and suggest some good hardware I've found.

What I did...
I spent several hours trying to get this working using the otg_mode modification, to no avail. The whole time I assumed the mod was probably successful, but that something was wrong with my mess of gender changers or power injection. Well, it turned out that (and I have since read this elsewhere) the otg_mode hack just wasn't sufficient. I HAD to use the flasher method instead. If you don't have a Linux machine from which to run flasher, this link explains how to do it from a virtual machine running under Windows. (NOTE: When I did this, I had to manually expose the 770 to the virtual machine by clicking on it in VMWare's VM->RemovableDevices->USBDevices menu.)

Once I tried this out and ran 'flasher --enable-usb-host-mode', everything just worked! I even had no problem mounting my 4gb thumb drive:
Incidentally, my current setup consists of OS2007HE running directly off of a 2gb mobile RSMMC card.


Hardware Configuration
1 @ mini-B (male) to A (female) adapter (attached to 770)
1 @ mini-B (male) to A (male) cable (between USB hub and bM-AM adapter)
1 @ noname miniature USB2 powered hub
1 @ USB2 mini keyboard (JME-8571 -- DOES NOT WORK!)

770 doesn't fully recognize this, so although most keys work, the caps/numlk/scrllk keys are stuck ON and consequently all of the letters that would normally double as a numeric keypad are stuck in numeric keypad mode. I have verified that it functions fine on a Windows PC though...

1 @ roll-up flexible keyboard

This works, but is very cumbersome, which defeats the purpose.

1 @ USB2 SD card reader (thumb drive that holds an SD card) + 4g card

I have to say that the cheap-o hub is PERFECT! It supplies power to the input port, so you don't have to inject power. Also, it's tiny. 1.75"x2.25". I highly recommend it.


Keyboards
The two keyboards I've tried are not going to work for me. The flexible/roll-up one is just impossible to use accurately. The other is nice and compact (8 1/2" x 4" x 1/2") and would be almost perfect, but I can't get it to be fully recognized (initialized?) by the 770, so half of the keyboard is stuck in numeric keypad mode.
So I ask your advice. If you have used a keyboard that was perfect, please let us know. Also, if you have a better understanding of the problem I'm having with mine, please share.

I bet there's probably a couple people out there with 770s that have a gem of a cable that they didn't realize they have.

Many 2.5" external USB enclosures come with a "power injector" cable that has a normal USB A connector, a power-only USB A connector, and a mini-A cable.

With this cable, ANY USB hub without an integrated upstream cable can get power injected upstream to the 770/N800.

If you get a gender changer, then you can use it with hubs that have an integrated upstream cable.

So you could, for example, use this battery-powered hub, and inject power from a downstream port upstream.

This thread has some good answers to my 'which keyboard' question...

http://www.internettablettalk.com/fo...ighlight=mount