RM0319 datasheet(133/368 Pages) STMICROELECTRONICS

133 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

133/368

OUT data memory structure

All endpoints that support out direction transactions (that is, endpoints receiving data from

the USB Host) must implement a memory structure according to the following

characteristics:

●

Each data buffer must have an associated descriptor which provides the status of the

buffer. Indeed, the buffer itself contains only raw data.

●

Each buffer descriptor is 4-quadlet length.

The out data memory structure is given in Figure 42. Table 38 reports the bits assignments

for out buffer status quadlet.

If the buffer status of the first descriptor is set to host ready (see BS field in Table 38), the

DMA fetches and processes its data buffer. Otherwise, the DMA skips to the next descriptor

until it reaches the end of the descriptor chain.

Figure 42.

Out data memory

Data Descriptor Pointer

OUT Buffer Status Quadlet

Reserved

Buffer Pointer

Next Descriptor Pointer

Status Quadlet for

Non Iso-chronous OUT

RxBytes

Rx Sts

15:0

26:16

29:28

31:30

Status Quadlet for

Iso-chronous OUT

Frame Number

RxBytes

Rx Sts

13:0

26:16

29:28

31:30

PID

15:14

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