On Mon, 27 Nov 2006, Ajay Jain wrote:
> Hello,
>
> We are implementing a USB peripheral controller driver for our
> proprietary hardware, an ARM based SOC. I have read the Linux gadget
> page on the linux usb website. A few things that I could conclude
> were:
>
> 1. We should be using the Linux gadget framework for the same, like
> the way its done for "lh7a40x_udc.c" (an example).
> 2. We would like to expose ourselves as a mass storage device to the
> host, therefore we would be using the suitable gadgets, eg.
> file-storage.o.
>
> I have a few questions here:
>
> 1. Assuming that I am exposing it as a mass storage device. Lets say
> that my file-system is lying on the SD card, and USB is only a means
> to carry the transfer. Now how does the file-storage module know about
> the SD card.
When you load the g_file_storage driver, you tell it what device to use
for its backing storage. Or you can tell it after loading, through a
sysfs attribute file. Read
http://www.linux-usb.org/gadget/file_storage.html
> How do these interact with each other?
g_file_storage reads and writes data to/from the card, as you would
expect.
> Is there some
> user-space daemon running?
Only if you start one up.
> 2. Assuming I were to expose this as a serial device to my PC. Now the
> bandwidth available on COMM ports is about 115Kbps while the USB
> bandwidth is about 12 Mbps. What would be the available bandwidth? My
> question arises from the fact that to use a serial device on the host
> side, I would be using the serial API's which could only be configured
> for the max serial bandwidth.
The available bandwidth is whatever your hardware and software will
support. There may be limits built into the g_serial driver but I don't
know what they are. USB is so much faster than normal serial
communications that it is not likely to be a limiting factor.
Alan Stern
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