Datasheet

Figure 32-6. Ping-Pong Overview

USB data packet

With Ping Pong

Without Ping Pong

Available time for data processing by CPU

to avoid NACK

Endpoint

single bank

Endpoint

dual bank

Bank0

Bank1

The Bank Select flag in EPSTATUS.CURBK indicates which bank data will be used in the next

transaction, and is updated after each transaction. According to EPSTATUS.CURBK,

EPINTFLAG.TRCPT0 or EPINTFLAG.TRFAIL0 or EPINTFLAG.TRCPT1 or EPINTFLAG.TRFAIL1 in

EPINTFLAG and Data Buffer 0/1 ready (EPSTATUS.BK0RDY and EPSTATUS.BK1RDY) are set. The

EPSTATUS.DTGLOUT and EPSTATUS.DTGLIN are updated for the enabled endpoint direction only.

32.6.2.12 Feedback Operation

Feedback endpoints are endpoints with same the address but in different directions. This is usually used

in explicit feedback mechanism in USB Audio, where a feedback endpoint is associated to one or more

isochronous data endpoints to which it provides feedback service. The feedback endpoint always has the

opposite direction from the data endpoint.

The feedback endpoint always has the opposite direction from the data endpoint(s). The feedback

endpoint has the same endpoint number as the first (lower) data endpoint. A feedback endpoint can be

created by configuring an endpoint with different endpoint size (PCKSIZE.SIZE) and different endpoint

type (EPCFG.EPTYPE0/1) for the IN and OUT direction.

Example Configuration for Feedback Operation:

• Endpoint n / IN: EPCFG.EPTYPE1 = Interrupt IN, PCKSIZE.SIZE = 64.

• Endpoint n / OUT: EPCFG.EPTYPE0= Isochronous OUT, PCKSIZE.SIZE = 512.

32.6.2.13 Suspend State and Pad Behavior

The following figure, Pad Behavior, illustrates the behavior of the USB pad in Device mode.

SAM D21 Family

USB – Universal Serial Bus

Datasheet Complete

DS40001882D-page 802