RM0319 datasheet(149/368 Pages) STMICROELECTRONICS

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RM0319

Fast Ethernet port (MII0)

Doc ID 022640 Rev 3

149/368

Receive descriptors

There are four different receive descriptors:

●

Receive descriptor 0, RDES0 (Table 48): it contains the status of the received frame,

the frame length and the descriptor ownership information.

●

Receive descriptor 1, RDES1 (Table 49): it contains the data buffer sizes and other bits

which controls the descriptor structure (chain/ring).

●

Receive descriptor 2, RDES2 (Table 50): it contains the address pointer to the first data

buffer in the descriptor.

●

Receive descriptor 3, RDES3 (Table 51): it contains the address pointer to the second

data buffer in the descriptor or the next descriptor (in case of chained structure).

Figure 47.

DMA descriptor format (Receive Descriptor, 32 bit)

Table 48.

Receive descriptor 0 (RDES0)

Bit

Name

Description

[31]

OWN

Own Bit. If set, it indicates that the descriptor is owned by the DMA of MAC.

If cleared, the descriptor is owned by the host.

[30]

AFM

Destination Address Filter Fail. If set, it indicates a frame that failed in the

DA filter in the MAC core.

[29:16]

Frame Length. These 14 bit field reports the byte length of the received

frame (including CRC and the 2 bytes appended to the frame when IP

checksum calculation is enabled and the received frame is not a MAC control

frame).

[15]

Error Summary. It is the logical OR of the following bits of this descriptor: [1],

[3], [4], [6], [10], [11] and [14].

[14]

Descriptor Error. If set, it indicates a frame truncation caused by a frame

that does not fit within the current descriptor buffers, and that the DMA does

not own the next descriptor.

[13]

SAF

Source Address Filter Fail. If set, it indicates a frame that failed in the SA

filter in the MAC core.

[12]

Length Error. If set, it states that the actual length of the frame received and

that the length/type field does not match.

RDES0

RDES1

RDES2

RDES3

Status [30:0]

Reserved

[31:29]

Buffer 2 Byte Count

[28:16]

Reserved

Buffer 1 Byte Count

[12:0]

Buffer 1 Address [31:0]

Buffer 2 Address [31:0] or Next Descriptor Address [31:0]

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[15:14]

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