Data Sheet

762
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
If there is no HANDSHAKE or corrupted HANDSHAKE, the EXTENDED/LPM pair of TOKENS will be transmitted again
until reaching the maximum number of retries as defined by the CTRL_PIPE.PERMAX in the pipe descriptor.
If the last retry returns no valid HANDSHAKE, the PINTFLAGn.PERR is set, and the STATUS_BK is updated in the pipe
descriptor.
All LPM transactions, should they end up with a ACK, a NYET, a STALL or a PERR, will set the PSTATUS.PFREEZE bit,
freezing the pipe before a succeeding operation. The user should unfreeze the pipe to start a new LPM transaction.
To exit the L1 STATE, the user initiate a DOWNSTREAM RESUME by setting the bit CTRLB.RESUME or a L1 RESUME
by setting the Send L1 Resume bit in CTRLB (CTRLB.L1RESUME). In the case of a L1 RESUME, the K STATE duration
is given by the BESL bit field in the EXTREG.VARIABLE field. See EXTREG.
When the host is in the L1 SLEEP state after a successful LPM transmitted, the device can initiate an UPSTREAM
RESUME. This will set the Upstream Resume Interrupt bit in INTFLAG (INTFLAG.UPRSM). The host should proceed
then to a L1 RESUME as described above.
After resuming from the L1 SLEEP state, the bit CTRLB.SOFE is set, allowing Start-of-Frame generation.