82801FB Datasheet, PDF (302/786 Pages) Intel Corporation – Intel I/O Controller Hub 6 (ICH6) Family

LAN Controller Registers (B1:D8:F0)
8.2.9
FLOW_CNTL—Flow Control Register
(LAN Controller—B1:D8:F0)
Offset Address: 19–1Ah
Default Value: 0000h
Attribute:
Size:
RO, R/W (special)
16 bits
Bit
Description
15:13
12
11
10
9
8
7:3
Reserved
FC Paused Low — RO.
0 = Cleared when the FC timer reaches 0, or a Pause frame is received.
1 = Set when the LAN controller receives a Pause Low command with a value greater than 0.
FC Paused — RO.
0 = Cleared when the FC timer reaches 0.
1 = Set when the LAN controller receives a Pause command regardless of its cause (FIFO reaching
Flow Control Threshold, fetching a Receive Frame Descriptor with its Flow Control Pause bit
set, or software writing a 1 to the Xoff bit).
FC Full — RO.
0 = Cleared when the FC timer reaches 0.
1 = Set when the LAN controller sends a Pause command with a value greater than 0.
Xoff — R/W (special). This bit should only be used if the LAN controller is configured to operate with
IEEE frame-based flow control.
0 = This bit can only be cleared by writing a 1 to the Xon bit (bit 8 in this register).
1 = Writing a 1 to this bit forces the Xoff request to 1 and causes the LAN controller to behave as if
the FIFO extender is full. This bit will also be set to 1 when an Xoff request due to an “RFD Xoff”
bit.
Xon — WO. This bit should only be used if the LAN controller is configured to operate with IEEE
frame-based flow control.
0 = This bit always returns 0 on reads.
1 = Writing a 1 to this bit resets the Xoff request to the LAN controller, clearing bit 9 in this register.
Reserved
Flow Control Threshold — R/W. The LAN controller can generate a Flow Control Pause frame
when its Receive FIFO is almost full. The value programmed into this field determines the number of
bytes still available in the Receive FIFO when the Pause frame is generated.
Bits 2:0 Free Bytes in RX FIFO Comment
000b
0.50 KB
Fast system (recommended default)
2:0
001b
010b
1.00 KB
1.25 KB
011b
1.50 KB
100b
1.75 KB
101b
2.00 KB
110b
2.25 KB
111b
2.50 KB
Slow system
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Intel^® I/O Controller Hub 6 (ICH6) Family Datasheet