RM0319 datasheet(135/368 Pages) STMICROELECTRONICS

135 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

135/368

IN data memory structure

All endpoints that support in direction transactions (that is, endpoints transmitting data to the

USB Host) must implement the memory structure given in Figure 43, where each in buffer

must be associated to a descriptor. Table 40 reports the bits assignments for in buffer status

quadlet.

The application fills the data buffer, then updates its status in the descriptor, and sets the

poll demand bit. Besides, the DMA fetches this descriptor and processes it, moving on in

this fashion until it reaches the end of the descriptor chain.

Table 39.

Out data memory: buffer status quadlet bit assignments (for Isochronous

OUT)

Bit

Name

Description

[31:30]

Buffer status.

This 2 bit field reports the status of the out buffer, according to encoding:

– 2'b00 Host ready. = The descriptor is available to be processed by DMA.

– 2’b01 DMA busy. = The DMA is still processing the descriptor.

– 2'b10 DMA done. = Buffer data transfer completed by DMA.

– 2’b11 Host busy. = The application is processing the descriptor.

[29:28]

Rx Sts

Receive status.

This 2 bit field reports the status of the received out data (according to

encoding), reflecting whether the out data has been correctly received or

some errors occurred:

– 2'b00 = Success.

– 2’b01 = DESERR (descriptor transfer error).

– 2'b10 = Reserved.

– 2’b11 = BUFFER (data transfer error).

Note: In particular, a DESERR receive status indicates that the out buffer

status is something other than Host ready (that is, BS not equal to 'b00)

during descriptor fetch.

[27]

If set, it indicates that this descriptor is the last one of the chain.

[26:16]

Frame

Number

11 bit frame number in which the current iso-out packet is received.

[15:14]

PID

ISO received data PID.

This 2 bit field indicates the data PID (according to encoding) for the

received ISO packet which is contained in the descriptor:

– 2’b00 = DATA0

– 2'b01 = DATA1

– 2'b10 = DATA2

– 2'b11 = MDATA

Note: The PID field is for HS ISO transactions only. For FS ISO transactions,

this field is don't care.

[13:00]

Rx Bytes

Received number of bytes.

The value of this field gives the received number of bytes.

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