Intel PCI User Manual

309

Reserved

IPGR2

IPGR1

IPGT

IPGT

9:0

X

IPG Transmit Time
Specifies the IPG time for back-to-back packet transmissions 
Measured in increments of the MAC clock:

• 8 ns MAC clock when operating @ 1 Gbps.
• 80 ns MAC clock when operating @ 100 Mbps.
• 800 ns MAC clock when operating @ 10 Mbps.

To calculate the actual IPG value for TBI applications, a value of 
10 (6 for the 82544GC/EI) should be added to the IPGT value.
For the IEEE 802.3 standard IPG value of 96-bit time, the value 
that should be programmed into IPGT is 10 (6 for the 82544GC/
EI).
To calculate the IPG value for 10/100/1000BASE-T applications, 
a value of four should be added to the IPGT value as four clocks 
are used by the MAC as internal overhead. The value that 
should be programmed into IPGT is 10 (8 for the 82544GC/EI).
These values are recommended to assure that the minimum 
IPG gap is met under all synchronization conditions.

IPGR1

19:10

X

IPG Receive Time 1
Specifies the length of the first part of the IPG time for non back-
to-back transmissions. During this time, the internal IPG counter 
restarts if any carrier event occurs. Once the time specified in 
IPGR1 has elapsed, carrier sense does not affect the IPG 
counter.
According to the IEEE802.3 standard, IPGR1 should be 2/3 of 
IPGR2 value.
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.

For IEEE 802.3 minimum IPG value of 96-bit time, the value that 
should be programmed into IPGR1 is eight.
IPGR1 is significant only in half-duplex mode of operation.