(no subject)

[torkell]

Plugging in an external USB hard disk apparently made my USB 3G modem disappear for a few moments. Weird.

The hard disk did seem to struggle to spin up - I'm guessing the combination of the spinup current and the draw of the 3G dongle was more than what the laptop was happy to deliver.

Now, in theory, USB devices are supposed to ask the controller how much power is available and draw no more than that, with an upper limit of 500mA. In practice, the rated spinup current on most hard disks (including this one) is much more than that. Isn't it wonderful the way standards get ignored?

Comments

[pewterfish.livejournal.com]

Yeah. Western Digital's "Passport" series and Linux is a particularly hilarious combination. If you sniff the bus, you can actually watch the following transaction take place when you plug one in.

WD: I want 300mA
Linux: Uh, no can do, chief. Don't got the power.
WD: Like, whatever, man, you can't tell me what to do.
*WD proceeds to draw about 450mA*
WD: The hell, man? Why you stiflin' ma creativity?

(lather, rinse, repeat until unplugged)

This pleases me not just because it flat ignores the return code that tells it the port can't supply that much power (a perfectly valid response, if an annoying one for a USB HDD), but also because it then proceeds to draw markedly more power than it requested. Feels like a workaround for something, but it sucks.