RM0319 datasheet(137/368 Pages) STMICROELECTRONICS

137 / 368 page

RM0319

USB 2.0 Device ports (UDC)

Doc ID 022640 Rev 3

137/368

Table 41.

In data memory:buffer status quadlet bit assignments (for isochronous)

Bit

Name

Description

[31:30]

Buffer status.

This 2 bit field reports the status of the in 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]

Tx Sts

Transmit status.

This 2 bit field reports the status of the transmitted in data (according to

encoding), reflecting whether the in data has been correctly transmitted

or some errors occurred:

– 2‘b00 = Success.

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

– 2‘b10 = Reserved.

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

[27]

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

[26:16]

Frame

Number (ISO)

11-bsit frame number in which the current iso-out packet is transmitted.

This 11 bit field gives the frame number in which the current iso-in packet

is transmitted, according to the following bits assignments:

[26:19] = Millisecond frame number.

[18:16] = Micro-frame number.

[15:14]

PID

Number of packets per microframe.

This 2 bit field indicates the number of packets per microframe for

isochronous (iso) in transfers during high-speed (hs) operation. The

application must program these bits in the descriptor (and they must be

the same for all descriptors of the same microframe) according to

encoding, such that the subsystem core returns an isochronous packet

with an appropriate data PID per frame:

– 2‘b00 = 1

– 2‘b01 = 1

– 2‘b10 = 2

– 2‘b11 = 3

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

transactions, this field is reserved.

[13:00]

Tx Bytes

(ISO)

Number of bytes to be transmitted.

The value of this field gives the number of bytes to be transmitted to USB

Host. In case of non-iso in, its 16 bit length allows values ranging from 0

to 64 kbytes. for iso in transactions, a maximum value of 16 kbytes is

allowed by the 14 bit length of the Tx bytes field.

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