RM0319 datasheet(130/368 Pages) STMICROELECTRONICS

130 / 368 page

USB 2.0 Device ports (UDC)

RM0319

130/368

Doc ID 022640 Rev 3

Figure 39.

In transaction flow in slave-only mode

Isochronous-in endpoints are handled similarly. In this case, the transfer of in data from the

application memory to the endpoint FIFO is not initiated by USB Host request tokens, but by

the application filling the TxFIFOs as soon as data is available. Isochronous endpoint data

must be filled in the TxFIFO only if the buffer is set for the current frame, which the

application can determine by reading the current active frame number from the CSR.

Out operation (Data transfer from USB Host)

When the UDC-AHB subsystem receives out data from the USB Host, it transfers the data

to the receive FIFO (RxFIFO) within the subsystem - if it has space available for the packet -

. If no space is available, the packet is retried. SETUP out packets are stored in a temporary

subsystem register before being loaded to the receive FIFO.

Once the packet is transferred to the RxFIFO, the subsystem sends an interrupt to the

application for the received packet. Then, the application reads the addressed endpoint’s

interrupt and status registers and the endpoint status register) and it is able to determine the

number of bytes received by the UDC-AHB Subsystem in the packet. After that, the

application reads from the RxFIFO this number of bytes.

Note:

The application reads from the address where the RxFIFO is mapped. The transaction flow

of out data from the USB Host to the application is shown in Figure 40.

Data

available?

Idle

Transaction

Read the

TxFIFO &Provide

IN data

Wait for Status

Transfer done

Status = ACK?

Generate INTR

and NAK

Yes

Idle

TxFIFO write

TxFIFO

available?

Yes

Write data

To TxFIFO

TxFIFO full?

Yes

Retry

Confirm Packet

in TxFIFO

Rewined READ

pointer

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