Chapter 8: Reset and Clocks
8–5
Clocks
November 2012
Altera Corporation
Arria V GZ Hard IP for PCI Express
Arria V GZ V Hard IP for PCI Express Clock Domains
illustrates the clock domains when using coreclkout_hip to drive the
Application Layer and the
pld_clk
of the Arria V GZ V Hard IP for PCI Express IP
Core.
As
indicates, the IP core includes three clock domains.
■
■
■
pclk
The transceiver derives
pclk
from the 100 MHz
refclk
signal that you must provide
to the device. The
PCI Express Base Specification 2.1
requires that the
refclk
signal
frequency be 100 MHz
300 PPM; however, as a convenience, you can also use a
reference clock that is 125 MHz
300 PPM.
The transitions between Gen1, Gen2, and Gen3 should be glitchless.
pclk
can be
turned off for most of the 1 ms timeout assigned for the PHY to change the clock rate;
however,
pclk
should be stable before the 1 ms timeout expires.
shows the frequency of
pclk
for Gen1, Gen2, and Gen3 variants.
Figure 8–5. Clock Domains and Clock Generation for the Application Layer
Note to
(1) The 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
Transceiver
250 or 500 MHz
pclk
coreclkout_hip
coreclkout
Application
Layer
pld_clk
(62.5, 125
or 250 MHz)
serdes_pll_locked
pld_core_ready
(1)
(coreclkout is derived from p_clk)
Table 8–2. pclk Clock Frequency
Data Rate
Frequency
Gen1 250
MHz
Gen2
500 MHz
Gen3
250 MHz