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AM335x: USB LPM L1 doable?

Orjan Friberg
Expert 1385 points

Hi,

The USB 2.0 LPM ECN (and later errata) defines a L1 (sleep) state between L0 (active) and L2 (suspend).  The L1 state is entered by sending a command to the device, as opposed to suspend which is implicit from 3 ms inactivity on the bus.  The exit from L1 is through resume signalling, just like the exit from suspend, but supposedly a lot shorter.

Has anyone looked at implementing this in StarterWare for device mode?  

  • Some software for decoding the LPM transaction will of course be needed.
  • The timing for the resume signalling is directly controlled by software through the POWER[RESUME] bit in USBHostResume() anyway, so that doesn't look too difficult.
  • In addition to this, we need to communicate a BESL value and the LPM L1 capability to the host through the device descriptor.

 

I didn't see any implementation of this in linux for the MUSB driver, only for the XHCI driver.

 

Thanks,

Orjan