Chapter 8: Reset and Clocks
8–7
Clocks
November 2012
Altera Corporation
Arria V GZ Hard IP for PCI Express
1
For Gen3, Altera recommends using a common reference clock (0 ppm) because when
using separate reference clocks (non 0 ppm), the PCS occasionally must insert SKP
symbols, potentially causing the PCIe link to go to recovery. Arria V GZ PCIe Hard IP
in Gen1 or Gen2 modes are not affected by this issue. Systems using the common
reference clock (0 ppm) are not affected by this issue. The primary repercussion of this
issue is a slight decrease in bandwidth. On Gen3 x8 systems, this bandwidth impact is
negligible. If non 0 ppm mode is required, so that separate reference clocks are used,
please contact Altera for further information and guidance.
Additional Clocks
Designs that include the Arria V GZ V Hard IP for PCI Express may require the
following additional clocks:
hip_reconfig_clk
The frequency range for this clock is 50–125 MHz. This is the clock signal for the Hard
IP reconfiguration interface. You can use this interface to change the value of global
configuration registers that are read-only at run time. Use of the reconfiguration
interface is optional.
reconfig_xcvr_clk
This is a free running clock with a frequency range of 100–125 MHz. This is the clock
input to the Transceiver Reconfiguration Controller which performs the transceiver
PHY reconfiguration functions required by Gen2 and Gen3 designs. For more
information, refer to
“Transceiver PHY IP Reconfiguration” on page 15–9
.
Clock Summary
summarizes the clocks for designs that include the Arria V GZ V Hard IP for
PCI Express IP Core.
Table 8–4. Required Clocks
Name
Frequency
Clock Domain
Clock Used by the Arria V GZ Hard IP for PCI Express IP Core
coreclkout_hip
125, or 250 MHz
Avalon-ST interface between the Transaction and Application
Layers.
pld_clk
62.5, 125 MHz, or 250 MHz
Application and Transaction Layers.
refclk
100 or 125 MHz
SERDES (transceiver). Dedicated free running input clock to
the SERDES block.
Other Clocks that May Be Required for PCI Express Designs
reconfig_xcvr_clk
100 –125 MHz
Transceiver Reconfiguration Controller.
hip_reconfig_clk
50–125 MHz
Avalon-MM interface for Hard IP dynamic reconfiguration
interface which you can use to change the value of read-only
configuration registers at run-time. This interface is optional.