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Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 12:
Constraining the Core
R
In addition, the example design provides pad locking on the TBI for several families. This
is included as a guideline only, and there are no specific I/O location constraints for this
core.
TBI Input Setup/Hold Timing
Input TBI Timing Specification
Figure 12-2
and
Table 12-1
illustrate the setup and hold time window for the input TBI
signals. These specify the worst-case data valid window presented to the FPGA device
pins. There is only a 2 ns data valid window of guaranteed data presented across the TBI
input bus. This must be correctly sampled by the FPGA devices.
Virtex-II, and Virtex-II Pro Devices
Figure 6-2
illustrates the TBI input logic provided by the example design for the Virtex-II
and Virtex-II Pro family. Although not illustrated, these families have input delay elements
(always of a fixed delay). These are also automatically inserted by the Xilinx tools and are
set to provide a zero-hold time. These input delays automatically meet input setup and
hold timing on the TBI without any specific constraints.
Spartan-3, Spartan-3E, and Spartan-3A Devices
Figure 6-3, page 72
illustrates the TBI input logic provided by the example design for the
Spartan-3 class family. DCMs are used on the
pma_rx_clk0
and
pma_rx_clk1
clock
paths as illustrated. Phase-shifting is then applied to the DCMs to align the resultant clocks
so that they correctly sample the 2 ns. TBI data valid window at the input DDR flip-flops.
The fixed phase shift is applied to the DCMs using the following UCF syntax.
INST "core_wrapper/tbi_rx_clk0_dcm" CLKOUT_PHASE_SHIFT = FIXED;
INST "core_wrapper/tbi_rx_clk0_dcm" PHASE_SHIFT = -10;
INST "core_wrapper/tbi_rx_clk0_dcm" DESKEW_ADJUST = 0;
Figure 12-2:
Input TBI timing
Table 12-1:
Input TBI Timing
Symbol
Min
Max
Units
t
SETUP
2.00
-
ns
t
HOLD
0.00
-
ns
t
SETUP
t
HOLD
rx_code_group[9:0]
PMA_RX_CLK0
t
SETUP
t
HOLD
PMA_RX_CLK1
