2–202
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Native Modes
Transmitter Data Path
The CPRI transmitter data path includes the transmitter phase
compensation FIFO, the 8B/10B encoder, and the 10:1 serializer. Layer 1
functions like Hyperframe framing that includes interleaving IQ data,
sync data, L1 inband protocol data, and so forth, that must be performed
in the FPGA logic array or external circuitry.
Receiver Data Path
The receiver data path includes the clock recovery unit (CRU),
1:10 deserializer, synchronization-state-machine-based word aligner,
8B/10B decoder, and receiver phase compensation FIFO.
The synchronization-state-machine-based word aligner is
programmable. You can select the number of bad code groups detected to
fall out of synchronization, the number of valid synchronization code
groups to acquire synchronization, and the number of good code groups
received to reduce the error count by 1.
You can use this programmability to implement the Loss of Signal (LOS),
Loss of Frame Synchronization (LOF), and the Remote Alarm Indication
(RAI) features in the FPGA logic array. The synchronization status is
reported on the
rx_syncstatus
port from the ALT2GXB. The
rx_syncstatus
signal is driven high when the programmed conditions
for synchronization state machine are met. Otherwise, it is driven low to
indicate loss of synchronization.
Link Delay Accuracy
Requirement R-19 in CPRI Specification V2.1 requires the CPRI link delay
accuracy (excluding the transmission medium delay) to be ± Tc/32,
where Tc is the length of a basic frame (260.42 ns). This requirement
mandates the total uncertainty in CPRI link latency to be less than
~16.3 ns.
To meet the strict CPRI link delay accuracy requirements, the Quartus II
software automatically adjusts the routing delays on the transmitter and
receiver phase compensation FIFO clocks. As a result of this delay
adjustment, the transmitter and receiver phase compensation FIFO
latency becomes constant.
1
The Quartus II software performs the delay adjustment to
minimize the uncertainty in link latency only in CPRI mode.