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314 Software Developer’s Manual
Register Descriptions
13.4.35 Adaptive IFS Throttle - AIT
AIFS (00458;R/W)
This register throttles back-to-back transmissions in the transmit packet buffer and delays their
transfer to the CSMA/CD transmit function. As a result, it can be used to delay the transmission of
back-to-back packets on the wire.
For the
82544GC/EI, this register can be used to increase the IPG value between transmitting
back-to-back packets on the wire and between frames while in half-duplex mode.
IPGR2 29:20 X
IPG Receive Time 2
Specifies the total length of the IPG time for non back-to-back
transmissions.
Measured in increments of the MAC clock:
• 8 ns MAC clock when operating @ 1 Gbps (82544GC/EI
only).
• 80 ns MAC clock when operating @ 100 Mbps
• 800 ns MAC clock when operating @ 10 Mbps.
In order to calculate the actual IPG value, a value of six should
be added to the IPGR2 value as six MAC clocks are used by the
MAC for synchronization and internal engines.
For the IEEE 802.3 standard IPG value of 96-bit time, the value
that should be programmed into IPGR2 is six (total IPG delay of
12 MAC clock cycles) According to the IEEE802.3 standard,
IPGR1 should be 2/3 of IPGR2 value.
IPGR2 is significant only in half-duplex mode of operation.
Reserved 31:30 X
Reserved
Read as 0b.
Should be written with 0b for future compatibility.
Field Bit(s)
Initial
Value
Description