ISOUSB111: Upstream behavior when downstream is disconnected in sync with SOF

Hi,

Thank you for reaching out and for sharing the details related to the issue.

Please note that the standard guidelines are to disconnect the device when the communication between the nodes has concluded. Disconnecting one side while other side of device is engaging in communication could lead the device in two different states. Hence, we do not recommend operating in such situation. Please plan to disconnect when the device side when the communication between the two sides has completed.

Let me know if you have any further questions, thanks.

Regards,
Koteshwar Rao

Dear Mr. Koteshwar Rao

Thank you for your prompt reply.
I think I should read the "Standard guideline" that I don't have. I would appreciate if you could let me know to obtain the "Standard guide line." Purchasing URL, Download URL, etc.

Best Regards,
Jun Aburai

Hi Jun,

Thanks for your response.

I am not sure if where exactly in the document the disconnection recommendations are stated, I will try and look for it and come back to you. Thanks.

Regards,
Koteshwar Rao

I would very much appreciate if you could give us any information regarding disconnection recommendation.

Hi Jun,

Apologies for the delayed response.
I couldn't find an explicit description or a statement regarding the point we are talking about. But from what I am aware, it is a guideline that states to initiate a disconnect event when the host is not transmitting. I am sorry that I couldn't find any references to this.

Let me know if I can help you with anything else, thanks.

Regards,
Koteshwar Rao

Dear Koteshwar Rao,

I appreciate very much for your time and effort in finding the guidelines.
I assume the guidelines you were looking for mentioned that downstream side is not able to disconnect at any time you want.
If I would like to disconnect at any time regardless the state of upstream side, I need to have additional circuitry in downstream side to monitor and then, when disconnected during SOF, the circuit delaying the disconnect state until the end of SOF state.
The above indicates that the issue can't be resolved by ISOUSB111 itself.

Recently, The external storage media removal policy for Windows changed as below, I think this causes above situation.
Please refer...
learn.microsoft.com/.../change-default-removal-policy-external-storage-media

Please correct me if my understanding wrong.

Best Regards,
Jun Aburai

Hi Jun,

Thank you for your inputs. Yes, your understanding is correct. When isolator is used, the MCU gets separated from the direct connection to the bus. Since the isolator has two sides (host and peripheral), it requires that the two sides are in the same state for effective communication. But if MCU starts communication / SOF on host side just when the peripheral is disconnected, then the host and peripheral sides end up in different states.

If the peripheral side is monitored and the host knows immediately about the disconnection then it can stop from sending the SOF and avoid this conditions, like you mentioned.

Thanks for sharing the change in the external media removal policy, I understand Quick Removal now and I see why this can lead to the situation  you are facing. Thanks for sharing this.

Let me know if I can go ahead and close this discussion or if you have any further questions. Thanks.

Regards,
Koteshwar Rao