XAUI - david-macmahon/wiki_convert_test GitHub Wiki
Block: XAUI Transceiver (XAUI)
Block Author: Pierre Yves Droz, Henry Chen
Document Author: Jason Manley
Summary
XAUI block for sending and receiving point-to-point, streaming data over the BEE2 and iBOB's CX4 connectors. NOTE: A new version of this block is in development.
Mask Parameters
| Parameter | Variable | Description |
|---|---|---|
| Demux | demux | Selects the width of the data bus. 1 for 64 bits, 2 for 32 bits. |
| Port | port | Selects the physical CX4 port on the iBOB or BEE2. The iBOB has two ports; the BEE2 has two for the control FPGA and four for each of the user FPGAs. CORR is not used by CASPER. |
| Pre-emphasis | pre_emph | Selects the pre-emaphasis to use over the physical link. Default: 3 (see Xilinx documentation) |
| Differential Swing | swing | Selects the size of the differential swing to use in mV. Default: 800 (see Xilinx documentation) |
Ports
| Port | Dir | Data Type | Description |
|---|---|---|---|
| rx_get | in | boolean | Used to request the next data word from the RX buffer. |
| rx_reset | in | boolean | Resets the receive subsystem. |
| tx_data | in | ufix_64_0 or ufix_32_0 | Accepts the next data word (64 or 32 bits) to be transmitted. |
| tx_outofband | in | ufix_8_0 or ufix_4_0 | Accepts the next data word (8 bits if demux=1, 4 bits if demux=2) to be transmitted through the out-of-band channel. |
| tx_valid | out | boolean | Clocks the transmit data into the transceiver. Data is clocked into the buffer while this line is high. |
| rx_data | out | ufix_64_0 | Outputs the received data stream. |
| rx_outofband | out | ufix_8_0 or ufix_4_0 | Outputs the out-of-band received data stream. |
| rx_empty | out | boolean | Indicates that the receive buffer is empty. |
| rx_valid | out | boolean | Indicates that data has been received. |
| rx_linkdown | out | boolean | Indicates that the link is down (eg. faulty cable). |
| tx_full | out | boolean | Indicates the transmit buffer is full. |
| rx_almost_full | boolean | inherited | Indicates the receive buffer is full. |
Description
Demux
Perhaps a misnomer, this parameter describes the width of the data bus
rather than a selection of two muxed streams on one channel. At 156MHz
XAUI clock, the maximum transmission speed is 64bits * 156.25 MHz =
10Gbit/s. For BEE or iBOB designs clocked at rates above 156MHz,
clocking-in 64 bit data on every clock cycle would cause the XAUI
block's FIFO buffers to overflow. The demux option is provided which
halves the input data bus width to 32 bits and enables data to be
clocked-in on every FPGA clock cycle. Along with the data bus width, the
out of band bus width is also halved to 4 bits.
Out of band signals
Out of band signals are guaranteed to arrive at the same time as the
data word with which they were sent. Out-of-band data is only
transmitted across the physical link if the input to tx_outofband
changes and is clocked in as valid (tx_valid). In other words, if you
keep tx_outofband constant, no additional bandwidth is consumed (the
in-band signals are transmitted as normal). When data is clocked into
the transmitter, it will appear out the receiver as if the
tx_outofband and tx_data arrived simultaneously. Care should be
taken to ensure that the data clocked into tx_outofband and tx_data
does not exceed the XAUI's maximum transmission rate (approximately
10Gbps for 156.25MHz clock). Each change of tx_outofband (be it one
bit or eight bits) requires 64 bits (a full word) to transmit. This bus
width is 8 bits if demux is not selected (set to 1), and 4 bits if it
is set to 2.