NRF52820-QDAA-R datasheet(378/437 Pages) NORDIC

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Peripherals

The data in the data stage (following the IN or OUT token) is transferred from or to the desired location

using EasyDMA.

The control endpoint buffer can be of any size.

After receiving the SETUP token, the USB controller will not accept (NAK) any incoming IN or OUT tokens

until the software has finished decoding the command, determined the type of transfer, and prepared for

the next stage (data or status) appropriately.

The software can stall a command when in the data and status stages, through the EP0STALL task, when

the command is not supported or if its wValue, wIndex or wLength parameters are wrong. The following

shows a stalled control read transfer, but the same mechanism (tasks) applies to stalling a control write

transfer.

SETUP

8 bytes

ACK

USB host

USB device

NAK

Setup stage

Data stage

STALL

Events & tasks

Software

Figure 138: Control read gets stalled

See the USB 2.0 Specification and relevant class specifications for rules on stalling commands.

Note: The USBD peripheral handles the SetAddress transfer by itself. As a consequence, the

software shall not process this command other than updating its state machine (see Device state

diagram), nor initiate a status stage. If necessary, the address assigned by the host can be read out

from the USBADDR register after the command has been processed.

6.26.9.1 Control read transfer

This section describes how the software behaves when responding to a control read transfer.

As mentioned earlier, the USB controller will not accept (NAK) any incoming IN tokens until software has

finished decoding the command, determining the type of transfer, and preparing for the next stage (data

or status) appropriately.

For a control read, transferring the data from memory into USBD will trigger a valid, acknowledged (ACK)

IN transaction on USB.

The software has to prepare EasyDMA by pointing to the buffer containing the data to be transferred. If no

other EasyDMA transfers are on-going with USBD, the software can send the STARTEPIN0 task, which will

initiate the data transfer and transaction on USB.

A STARTED event (with EPIN0 bit set in the EPSTATUS register) will be generated as soon as the EPIN[0].PTR

and .MAXCNT registers have been captured. Software may then prepare them for the next data

transaction.

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