Re: [Libnifalcon-devel] cube test

[Kyle M. (qDot) <ky...@no...>]

Stephen Sinclair wrote:
>
> First, this was on my laptop, which is a DV2020 HP, 64-bit AMD (though
> running 32-bit Ubuntu), with no USB hub, just directly plugging it
> into the laptop.
>
>   
Yeah, this is why I put the "powered hub" portion in my question about 
what you were running on. Throw a powered USB 2.0 hub in between your 
laptop and the falcon and you should see things clear up. Or keep 
reading if you want to know my thoughts on why this happens.

NOTE: The following is a completely untested and unresearched 
hypothesis. But it seems sound to me.

The falcon registers as a full speed, low power device, meaning the 
system should only give it 100mA. Assuming there's no transforming 
happening, that means they're splitting .5w between the ALL of the 
circuitry outside of the motors. The other paragraph you wrote about the 
wall socket being cold means you've obviously found that they're at 
least powering some parts of the falcon off the USB. Breaking it down, 
the falcon needs at least the FTDI, the bootloader chip, and the DSP 
(plus all the passive support components to run those, and who knows 
what else) to even be useful. It also lights up the lights slightly. I 
don't think .5w is enough to run all that stuff reliably.

So, why does it work on your desktop? Well, while the USB standard is 
quite clear about who should get what amounts of power, the 
manufacturing reality is a little different. If you'd like to know more 
about that, check out (WARNING: NSFW page. I should really move this 
article to somewhere that doesn't have large vibrator images in the 
header :) ):

http://www.slashdong.org/content/articles/how_shit_works/how_shit_works_usb_power.php

Laptops are going to be more stringent in their power requirements than 
desktops, in order to save battery, and probably follow the spec than 
desktops. That would be why your laptop goes all weird while your 
desktop works fine. Use a USB hub to work around this and make sure you 
get enough power no matter what.

So far, I've only tested this on macbooks, but it's fixed literally 
every single one I've had a problem on.