82598EB Datasheet, PDF (322/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - Register Descriptions
4.4.3.4.2 Flow Control Transmit Timer Value n – FCTTVn (0x03200 +
4*n[n=0..3]; RW)
Where each 32-bit register (n=0… 3) refers to two timer values (register 0 refers to timer 0 and 1,
register 1 refers to timer 2 and 3, etc.).
Field
TTV(2n)
TTV(2n+1)
Bit(s)
Initial
Value
Description
15:0
0x0
Transmit Timer Value 2n
Timer value included in XOFF frames as Timer (2n). For legacy 802.3X flow control
packets, TTV0 is the only timer that is used.
31:16
0x0
Transmit Timer Value 2n+1
Timer value included in XOFF frames as Timer 2n+1.
The 16-bit value in the TTV field is inserted into a transmitted frame (either XOFF frames or any pause
frame value in any software transmitted packets). It counts in units of slot time (usually 64 bytes).
Note: The 82598 uses a fixed slot time value of 64 byte times.
4.4.3.4.3 Flow Control Receive Threshold Low – FCRTL (0x03220 + 8*n[n=0..7];
RW)
Where each 32-bit register (n=0… 7) refers to a different receive packet buffer.
Field
Reserved
RTL[n]
Reserved
XONE[n]
Bit(s)
Initial
Value
Description
3:0
0x0
Reserved
The underlying bits might not be implemented in all versions of the 82598.
Must be written with 0x0.
18:4
0x0
Receive Threshold Low n
Receive packet buffer n FIFO low water mark for flow control transmission (256 bytes
granularity).
30:19
0x0
Reserved
Reads as 0x0. Should be written to 0x0 for future compatibility.
31
0b
XON Enable n
Per the receive packet buffer XON enable.
0b = Disabled
1b = Enabled.
This register contains the receive threshold used to determine when to send an XON packet and counts
in units of bytes. The lower four bits must be programmed to 0x0 (16-byte granularity). Software must
set XONE to enable the transmission of XON frames. Each time incoming packets cross the receive high
threshold (become more full), and then crosses the receive low threshold, with XONE enabled (1b),
hardware transmits an XON frame.
Flow control reception/transmission is negotiated through by the auto negotiation process. When the
82598 is manually configured, flow control operation is determined by the RFCE and RPFCE bits.
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