Altera Arria V Avalon-MM - Manual (Page 102)

For descriptions of the available reset signals, refer to Reset Signals, Status, and Link Training Signals.
Clocks
The Hard IP contains a clock domain crossing (CDC) synchronizer at the interface between the
PHY/MAC and the DLL layers. The synchronizer allows the Data Link and Transaction Layers to run at
frequencies independent of the PHY/MAC. The CDC synchronizer provides more flexibility for the user
clock interface. Depending on parameters you specify, the core selects the appropriate
coreclkout_hip
.
You can use these parameters to enhance performance by running at a higher frequency for latency
optimization or at a lower frequency to save power.
In accordance with the PCI Express Base Specification, you must provide a 100 MHz reference clock that is
connected directly to the transceiver.
As a convenience, you may also use a 125 MHz input reference clock as input to the TX PLL.
Related Information
PCI Express Base Specification 2.1 or 3.0
Clock Domains
Figure 6-5: Clock Domains and Clock Generation for the Application Layer
The following illustrates the clock domains when using
coreclkout_hip
to drive the Application Layer
and the
pld_clk
of the IP core. The Altera-provided example design connects
coreclkout_hip
to the
pld_clk
. However, this connection is not mandatory.
100 MHz
(or 125 MHz)
refclk
Hard IP for PCI Express
PHY/MAC
Clock
Domain
Crossing
(CDC)
Data Link
and
Transaction
Layers
TX PLL
PCS
250 or 500 MHz
pclk coreclkout_hip
Application
Layer
pld_clk
(62.5, 125
or 250 MHz)
serdes_pll_locked
pld_core_ready
Transceiver
As this figure indicates, the IP core includes the following clock domains:
pclk
The transceiver derives
pclk
from the 100 MHz
refclk
signal that you must provide to the device.
UG-01105_avmm
2014.12.15
Clocks 6-5
Reset and Clocks Altera Corporation
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