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difficult to model precisely. For this reason, several simulation-only attributes are provided
to work around these limitations.
SmartModel Attributes
SIM_GTPRESET_SPEEDUP
The SIM_GTPRESET_SPEEDUP attribute can be used to shorten the simulated lock time of
the shared PMA PLL.
If TXOUTCLK or RXRECCLK is used to generate clocks in the design, these clocks
occasionally flatline while the GTP_DUAL tile is locking. If a PLL or DCM is used to divide
TXOUTCLK or RXRECCLK, the final output clock is not ready until both the GTP_DUAL
tile and the PLL or DCM have locked.
required before a stable source from TXOUTCLK or RXRECCLK is available in simulation,
including the time required for any PLLs or DCMs used.
If either the PLL or the DCM is not used, the respective term can be removed from the lock
time equation. When simulating multirate designs where the shared PMA PLL frequency
or REFCLK frequency change, SIM_GTPRESET_SPEEDUP must be set to FALSE.
Appendix F, "Advanced
SIM_PLL_PERDIV2
The GTP_DUAL tile contains an analog PLL to generate the transmit and receive clocks
out of a reference clock. Because HDL simulators do not fully model the analog PLL, the
GTP_DUAL Smartmodel includes an equivalent behavioral model to simulate the PLL
output. The SIM_PLL_PERDIV2 attribute is used by the behavioral model to generate the
PLL output as accurately as possible. It must be set to 1/2 the period of the shared PMA
PLL. See
SIM_RECEIVER_DETECT_PASS
The GTP_DUAL includes a TXDETECTRX feature that allows the transmitter to detect
whether its serial ports are currently connected to a receiver by measuring rise time on the
TXP/TXN differential pin pair (see
The GTP_DUAL SmartModel includes an attribute for simulating TXDETECTRX called
SIM_RECEIVER_DETECT_PASS. This attribute allows TXDETECTRX to be simulated for
each GTP transceiver without modelling the measurement of rise time on the TXP/TXN
differential pin pair.
SIM_RECEIVER_DETECT_PASS should be set to TRUE by default. When TRUE, the
attribute models a connected receiver, and TXDETECTRX operations will indicate a
receiver is connected. To model a disconnected receiver, SIM_RECEIVER_DETECT_PASS
for the transceiver is set to FALSE.
Power-Up and Reset
Link Idle Reset
To simulate correctly, the Link Idle Reset circuit described in
implemented and connected to each GTP_DUAL instance. This circuit is included
automatically when the Wizard is used to configure the GTP_DUAL instance.
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
≅
t
t
USRCLKstable
GTPRESETsequence
Clocking"illustrates multirate design examples.
"Examples," page 46
for how to calculate SIM_PLL_PERDIV2 for a given rate.
www.xilinx.com
Equation 3-1
provides an estimate of the time
t
t
+
+
locktimePLL
locktimeDCM
"PCI Express Receive Detect Support," page
Description
Equation 3-1
116).
"Reset," page 72
must be
43
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