Altera CPRI IP Core - Manual (Page 87)

Chapter 4: Functional Description 4–55
CPRI Protocol Interface Layer (Physical Layer)
December 2013 Altera Corporation CPRI MegaCore Function
User Guide
Descrambling
If the tx_prot_version field of the CPRI_TX_PROT_VER register ( Table 7–25 on
page 7–12 ) holds the value 2, and the CPRI data rate is 4915.2 Mbps, 6144.0 Mbps, or
9830.4 Mbps, the low-level CPRI receiver may need to descramble the incoming data,
depending on the values in the
CPRI_RX_SCR_SEED register.
When the rx_scr_act_indication field of the CPRI_RX_SCR_SEED register ( Table 7–27
on page 7–13 ) is set, the low-level CPRI receiver descrambles the data words
according to the CPRI V5.0 Specification, using the seed in the rx_scr_seed field of
the CPRI_RX_SCR_SEED register. The seed value may be zero, indicating the incoming
data is not scrambled.
Frame Synchronization
During frame synchronization, LOF is set to zero. LOS—the assertion of the gxb_los
signal—resets the frame synchronization state machine.
Figure 4–27 shows the frame synchronization state machine. If scrambling is
configured in the CPRI link partner (based on the value at Z.2.0 in the incoming CPRI
communication), additional actions and conditions apply on the state machine
transitions, according to the CPRI V5.0 Specification. The CPRI IP core sets the values
in the
CPRI_RX_SCR_SEED register according to these conditions.