Functional Description
Incoming pause frames consist of the below:
•
A 48-bit destination address equal to:
•
The reserved multicast destination address 01.80.C2.00.00.01, or
•
The SL_SA(47:0) input mac source address.
•
The 48-bit source address of the transmitting device.
•
The 16-bit length/type field containing the value 88.08
•
The 16-bit pause opcode equal to 00.01
•
The 16-bit pause_time. A pause-quantum is 512 bit-times.
•
Padding to 64-byte data length.
•
The 32-bit frame-check sequence (CRC word).
All quantities above are hexadecimal and are transmitted most-significant byte first. The least-significant
bit is transferred first in each byte.
The padding is required to make up the frame to a minimum of 64 bytes. The standard allows pause
frames longer than 64 bytes to be discarded or interpreted as valid pause frames. The CPGMAC_SL will
recognize any pause frame between 64 bytes and rx_maxlen bytes in length.
14.3.2.13 Packet Drop Interface
The packet drop interface supports an external packet drop engine. The port 1 (and port 2) CPGMAC_SL
receive FIFO VBUSP interface signals are CPSW_3G outputs. The receive packet interface has an
associated packet drop input P1_RFIFO_DROP (P2_RFIFO_DROP). An external packet drop engine may
“snoop” the received packet header and data to determine whether or not the packet should be dropped.
If the packet is to be dropped the external logic must assert the drop signal by no later than the second
clock after the end of packet (or abort) indication from the CPGMAC_SL. The drop signal should remain
asserted until the second clock after the end of packet (or abort) indication. If the packet is not to be
dropped then the drop signal should remain deasserted. The CPGMAC_SL section contains more
information on the receive FIFO VBUSP interface signals and end of packet indication.
14.3.2.14 Short Gap
The port 1 (and port 2) transmit inter-packet gap (IPG) may be shortened by eight bit times when enabled
and triggered. The tx_short_gap_en bit in the SL1_MacControl (SL2_MacControl) register enables the
gap to be shortened when triggered. The condition is triggered when the port 1 (port 2) transmit FIFO has
a user defined number of FIFO blocks used. The port 1 transmit FIFO blocks used determines if the port 1
gap is shortened, and the port 2 transmit FIFO blocks used determines if the port 2 gap is shortened. The
CPSW_Gap_Thresh register value determines the port 1 short gap threshold, and the
CPSW_Gap_Thresh register value determines the port 2 short gap threshold.
14.3.2.15 Switch Latency
The CPSW_3G is a store and forward switch. The switch latency is defined as the amount of time
between the end of packet reception of the received packet to the start of the output packet transmit.
Mode
Latency
Gig (1000)
880ns
100
1.3us
10
6.5us
1209
SPRUH73H – October 2011 – Revised April 2013
Ethernet Subsystem
Copyright © 2011–2013, Texas Instruments Incorporated