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Android 7 Host on iMX7D - USB Auto-suspend Issue for Modem Peripheral

Question asked by sushant thakur on May 28, 2019
Latest reply on May 29, 2019 by igorpadykov

We have a LTE Modem peripheral connected over USB to iMX7D host. Host is running Android OS 7.1.2r9. 

There are two types of Suspend-Resume/Wakeup:

- Host to Modem Resume (working as expected)

- Modem to Host Wakeup (has an issue, please read on)

According to the Modem vendor, in a working case of Modem to Host Wakeup:  K state gets initiated and is maintained by modem for 5ms, following which within 500us Host takes over and maintains K state for rest of the 20ms. 
However on most occasions, the K state initiated by Modem for 5ms, however the Host does not maintain the K state completing the 20ms. Thus Auto-suspend does not work as expected.

USB Analyzer analysis is attached.