AM5728: USB gadget mode

xixi

Expert 2990 points

Other Parts Discussed in Thread: AM5728

HI all:

Just now we developed an am5728 custom board.

We want to use the USB2 to gadget storage mode.

The below is my test command

modprobe g_mass_storage file=/dev/mmcblk1p1 stall=0 removable=1

Now the windows PC can identify the USB device and can copy the file from the USB device.

While when we changed something such as touch a file or remove a file in am5728 board's /run/media/mmcblk1p1.

The Windows PC can not see the changes.

We also changed the command like this

modprobe g_mass_storage file=/dev/mmcblk1p1 cdrom=0 stall=0 removable=1 nofua=1

modprobe g_mass_storage file=/dev/mmcblk1p1 cdrom=0 stall=0 removable=1 nofua=0

The result is the same.

So how can we solve this issue?

My processor sdk is 3.3 version, The kernel is 4.4.41.

The below is my Schematic

Thanks

regards

xixi

over 8 years ago

0 Yordan Kovachev over 8 years ago

TI__Guru**** 161600 points

Hi,

I've notified the factory team. Their feedback will be posted here.

Best Regards,
Yordan

0 Bin Liu over 8 years ago

TI__Guru**** 171361 points

xixi said:

Now the windows PC can identify the USB device and can copy the file from the USB device.
While when we changed something such as touch a file or remove a file in am5728 board's /run/media/mmcblk1p1.
The Windows PC can not see the changes.

This result is expected. Write access simultaneously to the g_mass_storage backend is not supported. Here is quote from http://www.linux-usb.org/gadget/file_storage.html:

AN IMPORTANT WARNING! While MSG is running and the gadget is connected
to a USB host, that USB host will use the backing storage as a private
disk drive. It will not expect to see any changes in the backing storage
other than the ones it makes. Extraneous changes are liable to corrupt
the filesystem and may even crash the host. Only one system (normally,
the USB host) may write to the backing storage, and if one system is
writing that data, no other should be reading it. The only safe way to
share the backing storage between the host and the gadget's operating
system at the same time is to make it read-only on both sides.

And here https://stackoverflow.com/questions/35018792/how-does-embedded-linux-detect-file-is-modified-through-usb-gadget-update-file explains some of the reasons.

0 xixi over 8 years ago in reply to Bin Liu

Expert 2990 points

HI Bin Liu:

Thanks for your reply.

Now if the USB host changed the backing storage, whether the MSG(AM5728) would see the changes!

Thanks

regards

0 xixi over 8 years ago in reply to xixi

Expert 2990 points

Dear Bin Liu:

Could you tell me,

if the USB host changed the backing storage, whether the MSG(AM5728) would see the changes!

Thanks

regards

0 xixi over 8 years ago in reply to xixi

Expert 2990 points

HI all:

Anyone can help me about this issue,

Thanks

regards

0 Bin Liu over 8 years ago in reply to xixi

TI__Guru**** 171361 points

xixi said:
Now if the USB host changed the backing storage, whether the MSG(AM5728) would see the changes!

Based on the information I linked in my previous post, the answer is no, both systems (the USB host and that on AM57x) don't sync together, this is not MSG gadget is designed for.

0 xixi over 8 years ago in reply to Bin Liu

Expert 2990 points

Dear Bin Liu

Thanks for your reply

It solve my issues

regards

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AM5728: USB gadget mode