Data Sheet

Ethernet Controller I210 —Interconnects
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3.1.4.6 Flow Control
3.1.4.6.1 I210 Flow Control Rules
The I210 implements only the default Virtual Channel (VC0). A single set of credits is maintained for
VC0.
Rules for FC updates:
• The I210 maintains four credits for NPD at any given time. It increments the credit by one after the
credit is consumed and sends an UpdateFC packet as soon as possible. UpdateFC packets are
scheduled immediately after a resource is available.
• The I210 provides four credits for PH (such as for four concurrent target writes) and four credits for
NPH (such as for four concurrent target reads). UpdateFC packets are scheduled immediately after
a resource becomes available.
• The I210 follows the PCIe recommendations for frequency of UpdateFC FCPs.
3.1.4.6.2 Upstream Flow Control Tracking
The I210 issues a master transaction only when the required FC credits are available. Credits are
tracked for posted, non-posted, and completions (the later to operate with a switch).
3.1.4.6.3 Flow Control Update Frequency
In any case, UpdateFC packets are scheduled immediately after a resource becomes available.
When the link is in the L0 or L0s link state, Update FCPs for each enabled type of non-infinite FC credit
must be scheduled for transmission at least once every 30 µs (-0%/+50%), except when the Extended
Sync bit of the Control Link register is set, in which case the limit is 120 µs (-0%/+50%).
3.1.4.6.4 Flow Control Timeout Mechanism
The I210 implements the optional FC update timeout mechanism.
The mechanism is activated when the link is in L0 or L0s Link state. It uses a timer with a limit of
200 µs (-0%/+50%), where the timer is reset by the receipt of any Init or Update FCP. Alternately, the
timer can be reset by the receipt of any DLLP.
Table 3-9. Allocation of FC Credits
Credit Type Operations Number Of Credits
Posted Request Header (PH)
Target Write (one unit)
Message (one unit)
Four units
Posted Request Data (PD)
Target Write (Length/16 bytes=1)
Message (one unit)
MAX_PAYLOAD_SIZE/16
Non-Posted Request Header (NPH)
Target Read (one unit)
Configuration Read (one unit)
Configuration Write (one unit)
Four units
Non-Posted Request Data (NPD) Configuration Write (one unit) Four units
Completion Header (CPLH) Read Completion (N/A) Infinite (accepted immediately)
Completion Data (CPLD) Read Completion (N/A) Infinite (accepted immediately)