STMicroelectronics SPEAr300, Reference Manual

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RM0082 HS_Media independent interface (MII)
Doc ID 018672 Rev 1 513/844
24.4.2 Receive descriptors
As for Transmit Descriptors above, there are four different Receive Descriptors:
●
Receive descriptor 0, RDES0 ( Table 418 ): it contains the status of the received frame,
the frame length and the descriptor ownership information.
● Receive descriptor 1, RDES1 ( Table 419 ): it contains the data buffer sizes and other
bits which controls the descriptor structure (chain/ring).
●
Receive descriptor 2, RDES2 ( Table 420 ): it contains the address pointer to the first
data buffer in the descriptor.
● Receive descriptor 3, RDES3 ( Table 421 ): it contains the address pointer to the second
data buffer in the descriptor or the next descriptor (in case of chained structure).
Figure 53. DMA descriptor format (Receive Descriptor, 32 bit)
Table 418. 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] FL
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] ES
Error Summary. It is the logical OR of the following bits of this descriptor: [1],
[3], [4], [6], [10], [11] and [14].
[14] DE
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] LE
Length Error. If set, it states that the actual length of the frame received and
that the length/type field does not match.
O
W
N
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]
0
31
Ctrl
[15:14]
C
T
R
L