82598EB Datasheet, PDF (65/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - PCIe
ordering attribute as well (assuming that system logic supports both attributes). In fact,
some chipsets require that relaxed ordering is set for no-snoop to take effect.
No snoop is enabled by clearing the NS_DIS bit in the Extended Device Control (CTRL_EXT) register –
(0x00018; RW). The actual setting of no snoop is done for LAN traffic by the host through DCA registers
and for headers redirection through an EEPROM setting.
3.1.1.7.5 No Snoop and Relaxed Ordering for LAN Traffic
Software might configure no-snoop and relax order attributes for each queue and each type of
transaction by setting the respective bits in the DCA_RXCTRL and TCA_TXCTRL registers. Table 3-6 lists
the default behavior for the No-Snoop and Relaxed Ordering bits for LAN traffic when I/OAT 2 is
enabled.
Table 3-6. LAN Traffic Attributes
Transaction
Rx Descriptor Read
Rx Descriptor Write-Back
Rx Data Write
Rx Replicated Header
Tx Descriptor Read
Tx Descriptor Write-Back
Tx Data Write
No Snoop default
N
N
Y
N
N
N
N
Relaxed Ordering
default
Y
N
Y
Y
Y
Y
Y
Comments
Read-only. Must never
be used for this traffic.
See note and the section
that follows.
Note: RX payload no-snoop is also conditioned by the NSE bit in the receive descriptor.
3.1.1.7.5.1 No Snoop Option for Payload
Under certain conditions, which occur when I/OAT 2 is enabled, software knows that it is safe to
transfer a new packet into a certain buffer without snooping on the FSB. This scenario occurs when
software is posting a receive buffer to hardware that the CPU has not accessed since the last time it was
owned by hardware. This might happen if the data was transferred to an application buffer by the data
movement engine. In this case, software should be able to set a bit in the receive descriptor indicating
that the 82598 should perform a no-snoop transfer when it eventually writes a packet to this buffer.
When a no-snoop transaction is activated, the TLP header has a no-snoop attribute in the Transaction
Descriptor field. This is triggered by the NSE bit in the receive descriptor.
3.1.1.8 Flow Control
3.1.1.8.1 82598 Flow Control Rules
The 82598 implements only the default Virtual Channel (VC0). A single set of credits is maintained for
VC0.
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