More on Droid host mode

I’ve had a few days hacking on the Droid now (with some fun results that I’ll write up in a separate post in a moment), but I wanted to get back to a few things on Host mode USB first.

Firstly, adapters: these should work (3 links) to convert the Droid’s b-only socket to the correct A socket. Be careful of devices like this which will probably not work since the Droid has a Micro-B connector and that cable requires a Micro-A socket.

Next up, I’ve had a few folks ask for a review of the Droid comparing it to my G1. I’ll keep it quick – the screen and touch-response are far better, as is the keyboard, audio jack, speakers, CPU, and standard SD card (16Gb). It bugs me that there’s no pipe character on the keyboard (it is, after all, a *nix box), I don’t like the joypad mouse replacement and it bothers me that I have no cables or chargers for Micro-USB which is now the standard – all those Mini-USB dongles you’ve accumulated will soon be worthless. Whatever I think of it though I’ll forgive its flaws just purely because it supports USB host mode, even if the drivers are buggy as hell :)

Speaking of bugs, some workarounds and other notes:
- A powered USB hub is very handy if you’re playing with host mode. You can add and remove devices from the hub and as long as the hub stays plugged into the socket it all continues to work. Self-powered is good because the Droid can’t supply much power, although optionally-powered will also work because the Droid can supply small peripherals such as keyboards, mice, and small hubs.
- I was talking this all over with Mike Baker and it seems that the only reason you can’t switch the port back and forth between host mode and peripheral mode is because the gadget driver locks it – this is the driver that provides such things as ADB. If you prevent that driver from loading you should be able to switch back and forth by poking the right value in /proc/. Haven’t confirmed this yet but it sounds plausible.
- There’s an odd signal coming out of the power line on the Droid’s USB port if you shut the device down in host mode. The +5v drops to about +3.3v with about 0.5v of signal modulated on top. It’s definitely a signal (it responds to button input) and this is after the device has been powered down. Mike was going to investigate further and I’m planning to write a PIC decoder for it as well, so we’ll see where it goes – ideas for the signal source would be useful (I’ll post traces soon).
- If your USB peripherals just stop working at any point check for crash logs in dmesg. The driver does crash regularly, it doesn’t cause a kernel panic but does require a reboot to get the port working again.

The big fun (at least in my eyes) is the fact that I now have a working GSM base station running on my Droid. Watch this space for a howto coming up soon…:)

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One Response to More on Droid host mode

  1. gowthamj says:

    I was able to modify your idea and make one cable instead of a dongle and a cable.

    I recompile a new kernel with support for multiple usb devices and most of them were recognized and some of then worked with no issues at all. i had to use a powered hub.

    Thanks for you help. I have been trying to get this working for the last month or so. I was able to put it in host mode. but gave an error since i continued to use the otg cable.

    Thanks once again