Re: Some information on USB API

Hi,

On 4/30/07, Curran, Dominic <[email protected]> wrote:
>
> > Hi,
> >      I would like to know if there is any specific API that will be
> > used by the Applications that read/write to USB devices. For example
> > if a flash device is plugged into a system then the HCD will enumerate
> > the device and load the appropriate device driver for that flash
> > device to handle the device. Now say if the USB flash drive is mounted
> > as /dev/flashd. Then application will not even bother if he is a USB
> > device or  on board flash and just do the normal read/write from
> > /dev/flashd?
>
> Correct.
>
>
> >     When application does a read or even mount of the flash device how
> > is that information passed on to the device driver so that it can
> > convert that to specific Ctrl/Bulk transfer types and pass it on to
> > HCD?
>
> I believe the driver stack will look something like this:
>
> App that calls read()                       USERMODE
> ------------------------------------------
> File system driver (like ext3, fat32)       KERNEL MODE
> SCSI driver
>USB-Storage
> usbcore
> USB Host controller driver (like EHCI)
> PCI driver
> ------------------------------------------
> HARDWARE

I have a doubt here. I am not much familiar with USB-storage API but,
does this mean USB-Storage driver registers with the SCSI driver and
the information flow happens that way? I am confused because if we see
normal devices like serial port which have a device files like
/dev/ttyS0 they have a specific major, minor number which the driver
specifies while registering the I can see how the system calls get
routed through to the specific driver. But in the case of USB, when
the class specific driver registers with the respective subsystem
(USB-storage with SCSI/file system layer) how does the USB-Storage
driver specify to SCSI driver that it is taking care of the flash
device?

>

>
>
> >    Does the same process happen for all of the devices? Like if a USB
> > keyboard is connected and if I want to read from USB keyboard, I will
> > still read from standard keyboard interface?
>
> Yes, but obviously the driver stack looks a little different.
> In the case of HID I think it looks something like this...
>
> App like X                                  USERMODE
> ------------------------------------------
> HID                                         KERNEL MODE
> usbcore
> USB Host controller driver (like EHCI)
> PCI driver
> ------------------------------------------
> HARDWARE
>
>


Here how will HID layer differentiate between USB and PS2
mouse/keyboard? Will it read from both the interfaces?


> >    If I use libusb, can I get develop the driver in the user space and
> > get rid of the driver at kernel level?
>
> Yes.
> As long as you unload the driver or make sure it doesn't load to start
> with.
>
> >Also does libusb work on all
> > HCD's(
> >UHCI
>
> yes
>
> > EHCI
>
> yes
>
> > Mentor graphics MUSBHDRC etc.,)?
>
> Maybe.  Is there a linux driver for this ?
>
>

Yes, there is a driver for this..

>


-- 
Regards,
Meher

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