ST STM32L0x3 Reference Manual page 937

RM0367
[RXDP,RXDM] status
A device may require to exit from suspend mode as an answer to particular events not
directly related to the USB protocol (e.g. a mouse movement wakes up the whole system).
In this case, the resume sequence can be started by setting the RESUME bit in the
USB_CNTR register to '1 and resetting it to 0 after an interval between 1 ms and 15 ms (this
interval can be timed using ESOF interrupts, occurring with a 1 ms period when the system
clock is running at nominal frequency). Once the RESUME bit is clear, the resume
sequence will be completed by the host PC and its end can be monitored again using the
RXDP and RXDM bits in the USB_FNR register.
Note: The RESUME bit must be anyway used only after the USB peripheral has been put in
suspend mode, setting the FSUSP bit in USB_CNTR register to 1.
Table 165. Resume event detection (continued)
Wakeup event
"01" Root resume
"11" Not allowed (noise on bus)
Universal serial bus full-speed device interface (USB)
None
Go back in Suspend mode
RM0367 Rev 7
Required resume software action
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