Datasheet

The calculated CRC is valid on the next clock after the data is received.
24.3.6.3 MAC Receive Module
A receive operation is initiated when the MAC detects start-of-frame data (SFD). The MAC strips
the preamble and SFD before proceeding to process the frame. The header fields are checked for
the filtering and the FCS field is used to verify the CRC for the frame. The received frame is stored
in a buffer until the address filtering is performed. The frame is dropped in the MAC if it fails the
address filter.
Some of the functions of the MAC receive module are as follows:
■ Stripping the preamble, SFD and carrier extension of the Ethernet frame
■ Providing IEEE 1588 timestamping whenever an SFD is detected
■ Converting receive nibble data into bytes in MII mode
■ Decoding Length/Type field of the Ethernet frame
■ Auto-CRC/pad stripping if enabled in the EMACCFG register
■ Frame data and status buffering for received frames
■ Data path conversion of 8-bit data to 32-bit data
■ Frame filtering
■ Attaching calculated IP checksum input to frame
■ Detecting receiving pause frames and pausing the frame transmission for the delay specified
withing the received pause frame
■ Receive IP Checksum Verification
■ Performing destination and source address checking functions on all received frames and
reporting the address filtering status to the receive frame controller module.
24.3.6.4 MAC Receive Module CRC Generator
The receive CRC Generator is used to generate the 32-bit CRC for the FCS field of the Ethernet
frame. The encoding is defined by the following generating polynomial:
G(x) = x
32
+ x
26
+ x
23
+ x
22
+ x
16
+ x
12
+ x
11
+ x
10
+ x
8
+ x
7
+ x
5
+ x
4
+ x
2
+ x + 1
The calculated CRC is valid on the next clock after the data is received.
24.3.6.5 MAC Receive Frame Controller
If the RA bit is set in the Ethernet MAC Frame Filter (EMACFRAMEFLTR) register, offset 0x004,
the MAC Receive Frame Controller initiates the data transfer to the RX FIFO as soon as four bytes
of Ethernet data are received. At the end of the data transfer, the received frame status that includes
the frame filter bits (SA or DA filter fail) and status are also sent. These bits indicate to the application
whether the received frame has passed the filter controls. This module does not drop any frame on
its own in this mode.
If the RA bit is clear, the MAC Receive Frame Controller performs frame filtering based on the
destination/source address (the application still needs to perform another level of filtering if it decides
December 13, 20131630
Texas Instruments-Advance Information
Ethernet Controller