BCM5722 Programmer’s Guide
10/15/07
Broadcom Corporation
Page 161 Wake on LAN Mode/Low-Power Document 5722-PG101-R
The programmer must use the following equation to calculate the number of clock cycles required to match patterns at
10/100 wire-speed: (Length/2) * 3 MA clocks. The equation breaks down as follows:
- Determine the number of bytes in the RX Ethernet frame to compare. This value is a byte length.
- The WOL pattern checker can compare two bytes simultaneously. Divide length by two bytes and round up to
nearest integer value.
- The BCM5722 Ethernet controller compares 2 bytes every three memory arbiter (MA) clock cycles. Multiply
(Length/2) by three clock cycles.
• The following are example clock cycle calculations:
- Data stream length = 25 bytes
- 25 bytes/2 = 12.5 byte-pairs
- Round(12.5) = 13 byte-pairs
- 13 byte-pairs * 3 clocks/byte-pairs = 39 clocks (register ready)
- Data stream length = 83 bytes
- 83 bytes/2 = 41.5 byte-pairs
- Round(41.5) = 42 byte-pairs
- 42 byte-pairs * 3 clocks/byte-pair = 126 clocks (register ready)
WOL Streams
A stream is a comparison operation on RX frame(s). When the MAC is running at 10/100 Mbps wire speed, nine different
patterns can be compared against the RX frame(s). The BCM5722 Ethernet controller moves RX frame(s) into nine parallel
comparators, and the frame is matched simultaneously. The MAC is capable of filtering nine different patterns in 10/100
modes. The WOL pattern checker breaks frames into 2-byte pairs, so all nine comparators can begin matching data. In
Figure 62 on page 162, three Ethernet frames are compared against the nine available patterns.
Note: The BCM5722 Ethernet controller only supports one pattern stream at gigabit wire speed, so the length
field will always be the largest pattern size.
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