RM0319 datasheet(128/368 Pages) STMICROELECTRONICS

128 / 368 page

USB 2.0 Device ports (UDC)

RM0319

128/368

Doc ID 022640 Rev 3

Figure 38.

Out transaction flow in DMA mode

High-bandwidth isochronous (ISO) transfers

In case of out packets (that is, coming from USB Host), each descriptor stores one

maximum packet size of data. The data PID associated with the packet is available in the

PID field, bits [15:14], of the out data memory buffer status (OUT data memory structure on

page 133). If the microframe contains three packets, data and the corresponding data PID

are stored in three descriptors.

In case of in packets (transmitted to the USB Host), the application creates data of one

maximum packet size per descriptor. If the application must send three packets in the

microframe, the application must then create three descriptors. Data PID information must

be provided in the PID field, bits [15:14], of the in data memory buffer (IN data memory

structure on page 135).

11.4.4

Slave-only mode

In slave-only implementation, the application acts as an AHB master to read data from or to

write data to the memory-mapped subsystem FIFOs, and the UDC-AHB subsystem

operates as an AHB slave for both data and CSRs transfers.

The USB Host initiates USB traffic and the application responds to all the USB Host’s

commands. In this mode, the UDC-AHB subsystem can only be used in device-type

applications, and before any operation the application must completely configure the

necessary CSRs. All data transfers are interrupt-driven, except iso-in and interrupt-in

transfers, which are periodic.

The slave-only mode is typically implemented either in applications with limited complexity

software, or when the subsystem has a dedicated master for data processing.

RxFIFO

available?

Idle

OUT

Transaction

Write the OUT

Data in the

RxFIFO

Wait for

Status

Success

or ISO

Yes

ISO

Transfer?

Send

NAK

Got Status

Flush the

data

Yes

Confirm

data

Get

Descriptor

Yes

DMA

Enabled?

Generate

BNA INTR

Buffer

Initialized?

Yes

Transfer

OUT data To

host memory

Transfer

done

Update

descriptor

status and

generate INTR

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