On Fri, 10 Mar 2006, Shakthi Kannan wrote:

> Greetings!
> 
> I need to know your suggestions/views on implementing
> a shared secondary storage device while using the
> system as USB A-host (host) and USB B-peripheral mode
> (device).
> 
> Basically, I am using SD/MMC card to copy files when
> the system is in the host mode. I would like to use
> the same SD/MMC card as a secondary storage when in
> device mode, i.e., when the USB end on the system is
> connected to a host PC. 
> 
> Option 1: So, I will have to remove the SD/MMC driver
> and write a separate driver for interpreting USB data
> with sector read/write info sent from the host PC and
> do the read/writes to SD/MMC on the system? 

No.  Why would you do that?  There already are drivers in the kernel for 
interpreting USB data from the host (g_file_storage) and doing 
reads/writes to the SD/MMC card.  You don't have to remove them and 
write your own.

> Removing the SD/MMC driver is essential to avoid
> memory write conflicts. Or, is it possible to still
> have the SD/MMC card readable from the system?

I don't understand your comment.  Even when the card is readable from your 
system, there won't be any conflicts if you simply avoid reading it.  For 
example, make sure it isn't mounted.

> Option 2: Use gadget drivers for read/write info
> provided from the host PC?

That's what I would do.

> Option 3: Any other?

You mean, are the any options besides (1) writing your own drivers or (2) 
using the kernel's built-in drivers?  The only other possibility is (3): 
get someone else to write the drivers for you.

Alan Stern



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