RM0319 datasheet(125/368 Pages) STMICROELECTRONICS

125 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

125/368

Besides, all control endpoints implement an additional 16-byte buffer to store SETUP data.

The SETUP data structure (detailed in RM0321: SPEAr320S address map and registers)

does not implement a linked-list structure.

Figure 36.

Linked-list memory structure in DMA mode

In DMA mode, before starting any action, the application must both initialize the buffer

descriptor chains in the DMA data memory structure for all active endpoints of the UDC-

AHB subsystem, and configure the required CSRs during the USB reset.

A brief description of both in and out operation in DMA mode.

11.4.2

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 corresponding TxFIFO for data

availability. If data is available, the TxFIFO is read and the data is provided to the UDC for

transfer to USB Host. In contrast, if the TxFIFO is empty (no data), the UDC-AHB

subsystem sends an interrupt to the application and the UDC sends a NAK handshake to

the USB Host connected to that endpoint.

On receiving the interrupt, at first the application probes the endpoint interrupt register, to

determine which endpoint has requested the interrupt. Having determined this endpoint,

then the application probes the endpoint status register, to determine the interrupt’s cause.

Upon notification that this is an in token for a particular endpoint, the application updates the

addressed endpoint’s system memory buffer with data. Besides, the application reports to

the DMA the availability of such data by setting the poll demand bit in the subsystem’s

CSRs.

Note:

Each endpoint has a dedicated poll demand bit within CSRs, specifically in the endpoint-

specific endpoint control register.

Setup Buffer

Pointer

IN Data Descriptor

Pointer

Setup buffer Status Quadlet

In buffer Status Quadlet

Data

Next Pointer

Buffer

OUT Data

Descriptor Pointer

OUT buffer Status Quadlet

Next Pointer

Buffer

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