Altera CPRI IP Core - Manual (Page 27)

Chapter 3: Parameter Settings 3–3
Physical Layer Parameters
December 2013 Altera Corporation CPRI MegaCore Function
User Guide
Enable Autorate Negotiation
Autorate negotiation is the process of stepping down from a higher target CPRI line
rate to a lower target CPRI line rate if you are unable to establish a link at the higher
line rate. If your CPRI IP core has autorate negotiation enabled, and you program it to
step down from its highest target CPRI line rate to its lower target CPRI line rates
when it does not achieve frame synchronization, your CPRI IP core achieves frame
synchronization at the highest possible CPRI line rate in its range of potential line
rates, depending on the capability of its CPRI partner.
For information about the autorate negotiation feature, refer to Appendix B,
Implementing CPRI Link Autorate Negotiation .
Turn on the Enable auto-rate negotiation parameter to specify that your CPRI IP core
supports autorate negotiation. By default, this parameter is turned off.
Transceiver Starting Channel Number
You can specify the starting number for the CPRI IP core transceiver. For a CPRI IP
core master, the Master transceiver starting channel number specifies the starting
channel number for the transceiver.
For a CPRI IP core configured with slave clocking mode, the Slave transmitter
starting channel number
and Slave receiver starting channel number are two
separate parameters. Both must have values that are starting channel numbers
available in your design. The two numbers must be different but the Quartus II
software creates an FPGA configuration with a single slave transceiver.
If you instantiate multiple CPRI IP cores on the same device, you must ensure each
uses distinct transceiver channels.
These parameters are not available in Arria V, Cyclone V, and Stratix V devices.
Rx Elastic Buffer Depth
You can specify the depth of the Rx elastic buffer in the CPRI Receiver block. The
Receiver buffer depth
value is the log
2
of the Rx elastic buffer depth. Allowed values
are 4 to 8, inclusive.
The default depth of the Rx elastic buffer is 64, specified by the Receiver buffer depth
parameter default value of 6. For most systems, the default Rx elastic buffer depth is
adequate to handle dispersion, jitter, and drift that can occur on the link while the
system is running. However, the parameter is available for cases in which additional
depth is required.
1 Altera recommends that you set Receiver buffer depth to 4 in CPRI RE slave
variations.
CPRI IP core variations configured at a CPRI line rate of 9830.4 Mbps that target an
Arria V GT device do not include an Rx elastic buffer. However, this parameter affects
the depth of the RX buffer between the soft PCS and the Altera Transceiver Native
PHY IP core, instead. Refer to
Figure 4–4 on page 4–8 and Figure 4–5 on page 4–9 .
f
For information about the Altera Transceiver Native PHY IP core, refer to the Altera
Transceiver PHY IP Core User Guide .