Altera Low Latency Ethernet 10G MAC - Manual (Page 40)

To use the IEEE 802.3 flow control, set the following registers:
• On the transmit datapath:
• Set
tx_pfc_priority_enable
to 0 to disable the PFC.
• Set
tx_pauseframe_enable
to 1 to enable the IEEE 802.3 flow control.
• On the receive datapath:
• Set
rx_pfc_control
to 1 to disable the PFC.
• Set the
IGNORE_PAUSE
bit in the
rx_decoder_control
register to 0 to enable the IEEE 802.3 flow
control.
Pause Frame Reception
When the MAC receives an XOFF pause frame, it stops transmitting frames to the remote partner for a
period equal to the pause quanta field of the pause frame. If the MAC receives a pause frame in the middle
of a frame transmission, the MAC finishes sending the current frame and then suspends transmission for
a period specified by the pause quanta. The MAC resumes transmission when it receives an XON pause
frame or when the timer expires. The pause quanta received overrides any counter currently stored. When
the remote partner sends more than one pause quanta, the MAC sets the value of the pause to the last
quanta it received from the remote partner. You have the option to configure the MAC to ignore pause
frames and continue transmitting frames by setting the
IGNORE_PAUSE
bit in the
rx_decoder_control
register to 1.
Pause Frame Transmission
The MAC provides the following two methods for the client or connecting device to trigger pause frame
transmission:
•
avalon_st_pause_data
signal (
tx_pauseframe_enable[2:1]
set to 0)—You can connect this 2-bit
signal to a FIFO buffer or a client. Bit setting:
•
avalon_st_pause_data[1]
: 1—triggers the transmission of XOFF pause frames.
•
avalon_st_pause_data[0]
: 1—triggers the transmission of XON pause frames. The transmission
of XON pause frames only trigger for one time after XOFF pause frames regardless of how long the
avalon_st_pause_data[0]
signal is asserted.
If pause frame transmission is triggered when the MAC is generating a pause frame, the MAC ignores
the incoming request and completes the generation of the pause frame. Upon completion, if the
avalon_st_pause_data
signal remains asserted, the MAC generates a new pause frame and continues
to do so until the signal is deasserted. You can also configure the gap between successive XOFF
requests for using the
tx_pauseframe_quanta
register. XON pause frames will only be generated if the
MAC generates XOFF pause frames.
•
tx_pauseframe_control
register (
tx_pauseframe_enable[2:0]
set to 0x1)—A host (software) can
set this register to trigger pause frames transmission. Setting
tx_pauseframe_control[1]
to 1 triggers
the transmission of XOFF pause frames; setting
tx_pauseframe_control[0]
to 1 triggers the
transmission of XON pause frames. The register clears itself after the request is executed.
You can configure the pause quanta in the
tx_pauseframe_quanta
register. The MAC sets the pause
quanta field in XOFF pause frames to this register value.
Note: The new register field determines which pause interface takes effect.
3-18 Pause Frame Reception
UG-01144
2014.12.15
Altera Corporation Functional Description of LL Ethernet 10G MAC
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