NRF52820-QDAA-R datasheet(384/437 Pages) NORDIC

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Peripherals

6.26.11.2 Isochronous OUT transaction

When the host wants to send isochronous (ISO) data, it issues an OUT token on the isochronous endpoint,

followed by data.

The ISO OUT data endpoint has to be explicitly enabled by software through the ISOOUT0 bit in register

EPOUTEN.

The amount of last received ISO OUT data is provided in the SIZE.ISOOUT register. Software shall interpret

the ZERO and SIZE fields as presented in the following table.

ZERO

SIZE

Last received data size

Normal

No data received at all

Normal

1..1023

1..1023 bytes of data received

ZeroData

(not of interest)

Zero-length data packet received

Table 110: ISO OUT incoming data size

When EasyDMA is prepared and started, triggering a STARTISOOUT task initiates an EasyDMA transfer to

memory. Software shall synchronize ISO OUT transfers with the SOF events. EasyDMA uses the address in

ISOOUT.PTR and size in ISOOUT.MAXCNT for every new transfer.

If the EasyDMA transfer on the isochronous endpoint is not completed before the next SOF event, the

result of the transfer is undefined.

The maximum size of an isochronous OUT transfer in USB full-speed is 1023 bytes. The data buffer has to

be a multiple of 4 bytes and 32-bit aligned in Data RAM. However, the amount of bytes transferred on the

USB data endpoint can be of any size (up to 1023 bytes if not shared with an IN ISO endpoint).

If the last received ISO data packet is corrupted (wrong CRC), the USB controller generates an USBEVENT

event (at the same time as SOF) and indicates a CRC error on ISOOUTCRC in register EVENTCAUSE.

EasyDMA will transfer the data anyway if it has been set up properly.

USB host

USB device

OUT

DATA n+1

Start of frame

OUT

DATA n

Start of frame

OUT

DATA n+2

Start of frame

Events & tasks

Software

Figure 146: Isochronous OUT transfer

4463_156 v1.0

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