Thiruvengada Govindan wrote:
>
> Hi,
>
> The endpoint descriptor has a bit field that indicates whether the
> device attached is a "low speed" or "full speed" device. Now does the
> host controller interpret this field in any or is it ignored. I check
> the OHCI spec and it does not specify what a controller may use this
> information for. Any idea how this is used.
>
The HC driver does not use the descriptor field. It gets the speed
information from the root hub. When the USB is idle without a device
two resistors (15k) pulls both bus line to zero. A low
speed device has a pull up resistor (1.5k) on the D- Line.
A high speed device has a resistor on the D+ line.
Therefore a high speed device pulls the D+ line to 1 and D- is 0 and
a low speed device pulls D- to 1 and D+ to 0.
> The problem is like this: i'm using the USB stack on a MIPS based set
> top box to currently support cordless USB keyboard and mouse devices. I
> find that one port (port #2) always reports the device to be a full
> speed device (irrespective of the device i attach to the port). I'm
> using a USS312 controller. Has anybosy seen this same problem too ??,
> please clarify.
>
Maybe something is wrong with the resistors or cabels.
- Roman
> Port 1 works properly and i'm able to use it for either the mouse or the
> keyboard. I'm using kernel version 2.4.2. I've ported the HC driver for
> MIPS and am seeing this strange behavior when i use port 2.
>
> I even hard coded the "slow" field in the usb_device structure to "1"
> indicating a "low speed" device and i'm able to use both ports with no
> problems.
>
> Thanks for any help.
>
> Govindan
>
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