Data Sheet

Ethernet Controller I210 — Programming Interface
456
8.12.4 Retry Buffer Control – RETX_CTL (0x041C; RW)
This register controls the collision retry buffer.
8.12.5 DMA TX Control - DTXCTL (0x3590; R/W)
This register is used for controlling the DMA Tx behavior.
Field Bit(s) Initial Value Description
IPGT 9:0 0x08
IPG Back to Back.
Specifies the IPG length for back to back transmissions in both full and half duplex.
Measured in increments of the MAC clock:
8 ns MAC clock when operating @ 1 Gb/s.
80 ns MAC clock when operating @ 100 Mb/s.
800 ns MAC clock when operating @ 10 Mb/s.
IPGT specifies the IPG length for back-to-back transmissions in both full duplex and
half duplex. Note that an offset of 4 byte times is added to the programmed value to
determine the total IPG. As a result, a value of 8 is recommended to achieve a 12 byte
time IPG.
IPGR1 19:10 0x04
IPG Part 1.
Specifies the portion of the IPG in which the transmitter defers to receive events.
IPGR1 should be set to 2/3 of the total effective IPG (8).
Measured in increments of the MAC clock:
8 ns MAC clock when operating @ 1 Gb/s.
80 ns MAC clock when operating @ 100 Mb/s
800 ns MAC clock when operating @ 10 Mb/s.
IPGR 29:20 0x06
IPG After Deferral.
Specifies the total IPG time for non back-to-back transmissions (transmission
following deferral) in half duplex.
Measured in increments of the MAC clock:
8 ns MAC clock when operating @ 1 Gb/s.
80 ns MAC clock when operating @ 100 Mb/s
800 ns MAC clock when operating @ 10 Mb/s.
An offset of 5-byte times must be added to the programmed value to determine the
total IPG after a defer event. A value of 7 is recommended to achieve a 12-byte
effective IPG. Note that the IPGR must never be set to a value greater than IPGT. If
IPGR is set to a value equal to or larger that IPGT, it overrides the IPGT IPG setting in
half duplex resulting in inter-packet gaps that are larger then intended by IPGT. In this
case, full duplex is unaffected and always relies on IPGT.
Reserved 31:30 0x0
Reserved.
Write 0x0, ignore on read.
Field Bit(s) Initial Value Description
Water Mark 3:0 0x3
Retry buffer water mark. This parameters defines the minimal number of Qwords that
should be present in the retry buffer before transmission is started.
Reserved 31:4 0x0
Reserved.
Write 0x0, ignore on read.