RM0319 datasheet(127/368 Pages) STMICROELECTRONICS

127 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

127/368

Figure 37.

In transaction flow in DMA mode

11.4.3

Out operation (Data transfer from USB Host)

In the out direction, as soon as the UDC-AHB subsystem receives an out (or SETUP) data

from the USB Host (that is, when a packet of data is completed or - if thresholding is enabled

- a threshold is reached), it transfers the data to the buffers allocated to the endpoint in

application memory. Once the data is transferred, the subsystem updates the status of the

received data to the buffer’s status quadlet.

SETUP data is transferred to a 16-byte SETUP buffer. The pointer for this buffer is indicated

in the Endpoint setup buffer pointer register). Out data is transferred to the buffers indicated

by the descriptor, and the pointer for these descriptors is programmed in the CSRs.

Note:

The SETUP data directly addresses the buffers, while regular out data addresses the out

data buffers indirectly.

The transaction flow for all out endpoints is similar. The only difference is that isochronous

(iso-out) data is tagged with the frame number when the packet is received.

The transaction flow of out data from the USB Host to the application memory is given in

Figure 38.

Data

available?

Idle

Transaction

Read the

TxFIFO &Provide

IN data

Wait for Status

from USB host

Transfer done

Got ACK

Status?

Generate INTR

and NAK

Yes

Idle

Transfer data

From memory to

TxFIFO

Availabe?

Packet

Completely

Transferred?

Service other IN

requests and

return when done

Update Descriptor

Status

Yes

Rewined

READ pointer

Poll demand

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