NRF52820-QDAA-R datasheet(376/437 Pages) NORDIC

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Peripherals

The device shall ensure that it does not initiate a remote wake-up request before TWTRSM (according to

USB specification chapter 7) after the bus has entered idle state. Using the recommended resume value in

DPDMVALUE (rather than K) takes care of this, and postpones the RESUME state accordingly.

6.26.8 EasyDMA

The USBD peripheral implements EasyDMA for accessing memory without CPU involvement.

Each endpoint has an associated set of registers, tasks and events. EasyDMA and traffic on USB are tightly

related. A number of events provide insight of what is happening on the USB bus with a number of tasks

allowing an automated response to the traffic.

Note: Endpoint 0 (IN and OUT) are implemented as control endpoint. For more information, see

Control transfers on page 377.

Registers

Enabling endpoints is controlled through the EPINEN and EPOUTEN registers.

The following registers define the memory address of the buffer for a specific IN or OUT endpoint:

• EPIN[n].PTR, (n=0..7)

• EPOUT[n].PTR, (n=0..7)

• ISOIN.PTR

• ISOOUT.PTR

The following registers define the amount of bytes to be sent on USB for next transaction:

• EPIN[n].MAXCNT, (n=0..7)

• ISOIN.MAXCNT

The following registers define the length of the buffer (in bytes) for next transfer of incoming data:

• EPOUT[n].MAXCNT, (n=1..7)

• ISOOUT.MAXCNT

Since the host decides how many bytes are sent over USB, the MAXCNT value can be copied from register

SIZE.EPOUT[n] (n=1..7) or register SIZE.ISOOUT.

MaxPacketSize from the device descriptor or

wLength from the SETUP command, whichever is the least.

The .AMOUNT registers indicate how many bytes actually have been transferred over EasyDMA during the

last transfer.

Stalling bulk/interrupt endpoints is controlled through the EPSTALL register.

Note: Due to USB specification requirements, the effect of the stalling control endpoint 0 may be

overridden by hardware, in particular when a new SETUP token is received.

EasyDMA will not copy the SETUP data to memory (it will only transfer data from the data stage). The

following are separate registers in the USBD peripheral that have setup data.

• BMREQUESTTYPE

• BREQUEST

• WVALUEL

• WVALUEH

• WINDEXL

• WINDEXH

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NRF52820-QDAA-R Datasheet(PDF) 376 Page - Nordic Semiconductor

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