RM0090: Reference manual - STMicroelectronics

Ethernet (ETH): media access control (MAC) with DMA controller RM0090
Receive status word
At the end of the Ethernet frame reception, the MAC outputs the receive status to the
application (DMA). The detailed description of the receive status is the same as for
bits[31:0] in RDES0, given in RDES0: Receive descriptor Word0 on page 957.
Frame length interface
In case of switch applications, data transmission and reception between the application and
MAC happen as complete frame transfers. The application layer should be aware of the
length of the frames received from the ingress port in order to transfer the frame to the
egress port. The MAC core provides the frame length of each received frame inside the
status at the end of each frame reception.
Note: A frame length value of 0 is given for partial frames written into the Rx FIFO due to overflow.
MII/RMII receive bit order
Each nibble is transmitted to the MII from the dibit received from the RMII in the nibble
transmission order shown in Figure 336. The lower-order bits (D0 and D1) are received first,
followed by the higher-order bits (D2 and D3).
Figure 336. Receive bit order
LSB
MII_RXD[3:0]
MSB
925/1416 Doc ID 018909 Rev 3
D0
D1
D2
D3
RMII_RXD[1:0]
LSB MSB
D0 D1
Di-bit stream
Nibble stream ai15633