AM3352: Linux/AM3352: Limitied number of active usb devices

Hi Bin Liu,

It sounds like this is the issue.

With the number of hubs and devices - is there a way to cross the limit of a total of 16 EPs?

As I mentioned the devices are FTDI (serial USB) ttyUSB, I don't need fast communication and don't need large FIFO

Thanks

Avner

Hi Avner,

It is up to the implementation in USB devices, but typically each USB hub uses one interrupt endpoint, and each USB-serial port uses one interrupt endpoint. It has nothing to do with FIFO size.

Hi Bin Liu,

Thank you for your reply!

Short explanation:

We have a board based on AM3352 - it should communicate many devices simultaneously (via serial device /dev/ttyUSBx).

The communication is that the host writes a message and then reads the answer immediately (the read is nonblocking, and I poll every few milliseconds for up to 1 second). Each USB device has its own thread for communication.

All devices are kept open all the time.

My question in the current constellation - is it possible to handle more devices than what I have today (up to 10-11 FTDI devices), if yes - what is the limit? and what I need to do in order to achieve it?

If the answer is that it impossible - will open/close the device for each transaction and schedule it so each time maximum devices will be open, allow me to handle more devices?

(Of course, I prefer the solution that will allow me not to change the current software architecture)

Thanks

Avner

Hi Avner,,

Avner Flesch said:

is it possible to handle more devices than what I have today (up to 10-11 FTDI devices), if yes - what is the limit? and what I need to do in order to achieve it?

Have you applied the kernel patch below? If not, using it probably will allow you to have a few more devices.

e2e.ti.com/.../3647465

Hi Bin Liu,

Thanks for your answer - I tried this patch and I didn't notice any improvement.

And I need to support up to 64 devices - Is there a way to support such setup except for an open-close device for each USB transaction?

Thanks

Avner

Hi Avner,

As explained in the other E2E thread referred above, due to the limitation of the number of endpoints, it is not possible to open all 64 devices if each uses at least one Interrupt endpoint.

Hi Bin Liu,

So, I guess limit the maximum number of concurrent open devices to 8 will solve the issue?

Another option, excuse me I am not an expert in USB - in my case (write a message to serial USB and then read the answer) is interrupt endpoint per USB port is a must?

Thanks

Avner

Hi Avner,

Avner Flesch said:

So, I guess limit the maximum number of concurrent open devices to 8 will solve the issue?

I am not sure what causes the issue, so I cannot tell if 8 devices will work.

Avner Flesch said:

- in my case (write a message to serial USB and then read the answer) is interrupt endpoint per USB port is a must?

No, the endpoint type is implemented in the USB device, it could be interrupt or bulk endpoints in USB-serial devices. You can check the endpoint information of a USB device by plug it in any Linux USB host then run command 'lsusb -v -d <vid:pid>' on the host.