RM0319 datasheet(129/368 Pages) STMICROELECTRONICS

129 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

129/368

In operation (Data transfer to USB Host)

If the UDC-AHB subsystem receives an in token from a USB Host for a non-isochronous

endpoint (such as, bulk, interrupt or control), it checks the associated TxFIFO (Endpoint

FIFO controller (Transmit FIFO controller) on page 122) for data availability. If data is

available, the UDC reads the data from the TxFIFO, otherwise if the TxFIFO does not

contain data, the UDC sends an interrupt to the application, and the USB Host retries the in

token.

Upon receiving the interrupt, at first the application reads the endpoint interrupt register to

determine which endpoint requested the interrupt, and then probes the endpoint status

Once the application determines that an in token for the endpoint requested the interrupt, it

writes the packet directly to the address where the associated TxFIFO is mapped. As soon

as the packet data has been completely written into the FIFO, the application performs then

a single write to a predefined address (pointed by the write confirmation register, of the

relevant in endpoint) indicating to the subsystem that the packet transfer is done.

When the USB Host retries the in token, the subsystem provides the associated endpoint

TxFIFO data to the UDC for transmission to the USB Host. The sequence of these events

for a non-isochronous (interrupt, bulk, or control) endpoint is shown in Figure 39.

Note:

The application does not receive status update regarding the packet, because the

subsystem must transmit this data. However, the application may flush the packet from the

relevant TxFIFO by setting the F bit in the endpoint control register.

RM0319 датащи(PDF) 129 Page - STMicroelectronics