Altera Triple Speed Ethernet MegaCore Function Bedienungsanleitung PDF herunterladen (Seite 50)

DescriptionRegister NameThreshold

The number of unwritten entries in the FIFO buffer before the buffer

is full. When the level of the FIFO buffer reaches this threshold, the

MAC function asserts the ff_rx_a_full signal. If the user

application is not ready to receive data (ff_rx_rdy = 0), the MAC

function performs the following operations:

• Stops writing data to the FIFO buffer.

• Truncates received frames to avoid FIFO buffer overflow.

• Asserts the rx_err[0] signal when the ff_rx_eop signal is

asserted.

• Marks the truncated frame invalid by setting the rx_err[3]

signal to 1.

If the RX_ERR_DISC bit in the command_config register is set to 1

and the section-full (rx_section_full) threshold is set to 0, the

MAC function discards frames with error received on the Avalon-

ST interface.

rx_almost_fullAlmost full

An early indication that the FIFO buffer is getting full. When the

level of the FIFO buffer hits this threshold, the MAC function

generates an XOFF pause frame to indicate FIFO congestion to the

remote Ethernet device. When the FIFO level goes below this

threshold, the MAC function generates an XON pause frame to

indicate its readiness to receive new frames.

To avoid data loss, you can use this threshold as an early warning

to the remote Ethernet device on the potential FIFO buffer

congestion before the buffer level hits the almost-full threshold. The

MAC function truncates receive frames when the buffer level hits

the almost-full threshold.

rx_section_emptySection

empty

The section-full threshold indicates that there are sufficient entries

in the FIFO buffer for the user application to start reading from it.

The MAC function asserts the ff_rx_dsav signal when the buffer

level hits this threshold.

Set this threshold to 0 to enable store and forward on the receive

datapath. In the store and forward mode, the ff_rx_dsav signal

remains deasserted. The MAC function asserts the ff_rx_dval

signal as soon as a complete frame is written to the FIFO buffer.

rx_section_fullSection full

Functional Description

Altera Corporation

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Receive Thresholds

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2014.06.30

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