■ 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.
20.3.4.4
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.
20.3.4.5
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
not to receive any bad frames like runt, CRC error frames, etc.) After receiving the destination or
source address bytes, the MAC Receive Frame Controller checks the filter-fail sign for an address
match. On detecting a filter-fail, the frame is dropped and not transferred to the application.
Note:
When the PMT module is configured for power-down mode, all received frames are dropped
and not forwarded to the application.
20.3.5
IEEE 1588 and Advanced Timestamp Function
The MAC module supports the IEEE 1588-2002 Timestamp Precision Time Protocol (PTP) and the
IEEE 1588-2008 Advanced Timestamp features. PTP enables precise synchronization of clocks in
measurement and control systems implemented with technologies such as network communication,
local computing, and distributed objects. The PTP applies to systems communicating by a local
area network supporting multicast messaging. This protocol enables heterogeneous systems that
include clocks of varying inherent precision, resolution, and stability to synchronize. The protocol
supports system-wide synchronization accuracy in the sub-microsecond range with minimal network
and local clock computing resources.
The PTP is transported over UDP/IP. The system or network is classified into master and slave
nodes for distributing the timing and clock information. Figure 20-8 on page 1441 shows the process
that PTP uses for synchronizing a slave node to a master node by exchanging PTP messages.
June 18, 2014
1440
Texas Instruments-Production Data
Ethernet Controller
