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Flow Control Receive Threshold High - FCRTH (02168h; R/W) — Intel
®
82575EB Gigabit Ethernet
Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 357
14.3.54 Flow Control Receive Threshold High - FCRTH
(02168h; R/W)
This register contains the receive threshold used to determine when to send an XOFF packet. The
complete register reflects the threshold in units of bytes. This value must be at maximum 48 bytes less
than the maximum number of bytes allocated to the Receive Packet Buffer (PBA, RXA), and the lower 4
bits must be programmed to 0b (16 byte granularity). The value of RTH should also be bigger than
FCRTL.RTL. Each time the receive FIFO reaches the fullness indicated by RTH, hardware transmits a
PAUSE frame if the transmission of flow control frames is enabled.
Flow control reception/transmission are negotiated capabilities by the Auto-Negotiation process. When
the 82575 is manually configured, flow control operation is determined by the CTRL.RFCE and
CTRL.TFCE bits.
14.3.55 Flow Control Refresh Threshold Value - FCRTV
(02460h; R/W)
RTL 15:4 0h Receive Threshold Low.
FIFO low water mark for flow control transmission. This field is in 16 bytes granularity.
Reserved 30:16 0h Reserved
Should be written with 0b for future compatibility.
Reads as 0b.
XONE 31 0b XON Enable
0b = Disabled.
1b = Enabled.
Field Bit(s)
Initial
Value
Description
Reserved 3:0 0000b Reserved
Must be written with 0b.
RTH 15:4 0h Receive Threshold High
FIFO high water mark for flow control transmission. This field is in 16 bytes granularity.
Reserved 19:16 0h Reserved
Must be set to 0b.
Reserved 31:20 0h Reserved
Should be written to 0b for future compatibility.
Reads as 0b.
Field Bit(s)
Initial
Value
Description
FC_refresh_th 15:0 0h Flow Control Refresh Threshold
This value indicates the threshold value of the flow control shadow counter; when the
counter reaches this value, and the conditions for PAUSE state are still valid (buffer
fullness above low threshold value), a PAUSE (XOFF) frame is sent to link partner.
If this field contains zero value, the Flow Control Refresh is disabled.
Reserved 31:16 - Reserved