Far-End Pma Loopback; Marginal Conditions And Limitations - Xilinx Virtex-5 RocketIO GTP User Manual

Chapter 9: Loopback
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The attribute PMA_COM_CFG[44:37] can be changed either statically by specifying the
value in the UCF file or dynamically by changing the content of the DRP address 26[6:3] to
1111. When switching from loopback mode to normal operation, the default value that is
set automatically by the RocketIO GTP Transceiver Wizard must be restored.

Far-End PMA Loopback

This mode uses the Near-End data source for generating and checking test data. The
loopback occurs after passing the serial-to-parallel converter of the PMA. This mode tests
the complete PMA section including the serial-to-parallel and parallel-to-serial
conversion. Almost the entire PCS section is bypassed because the RX serial inputs are
looped back to the TX serial outputs.

Marginal Conditions and Limitations

When the Far-End PMA loopback mode (100) is used, disregarding
PLL_RXDIVSEL_OUT, both PLL_TXDIVSEL_COMM_OUT and PLL_TXDIVSEL_OUT
must be set to 1. Refer to
settings.
In Far-End PMA loopback mode the TX buffer is borrowed for the parallel loopback path
to compensate for possible phase differences between the TX and RX parallel clocks. For
this reason, TX_BUFFER_USE must be TRUE when using this mode. This mode can only
be used for one transceiver at a time on any given tile due to clocking restrictions.
When one channel of a GTP_DUAL is placed in the Far-End PMA loopback mode, the TX
side of the other channel no longer operates reliably. Do not attempt nor expect reliable use
of the second channel while the first is in 100 loopback.
198
Turn the RX linear equalizer on by setting the active Low RXENEQB(0/1) signal equal
to 0.
Set RXEQMIX(0/1)[1:0] to 11.
Change PMA_COM_CFG[44:37] from the default value automatically set by the
RocketIO GTP Transceiver Wizard to 10101010. This setting for
PMA_COM_CFG[44:37] must only be used for loopback. With normal data,
performance will be affected.
Serial
TX-PMA
Serial
Figure 9-4: Far-End PMA Loopback
"Shared PMA PLL," page 60
www.xilinx.com
Figure 9-4 illustrates this mode.
Far-End GTP
P
a
r
TX-PCS
a
l
l
e
l
RX-PMA RX-PCS
for details about the TX divider
Virtex-5 RocketIO GTP Transceiver User Guide
UG196_c9_04_082906
UG196 (v1.3) May 25, 2007
R