Altera CPRI IP Core - Manual (Page 85)

Chapter 4: Functional Description 4–53
CPRI Protocol Interface Layer (Physical Layer)
December 2013 Altera Corporation CPRI MegaCore Function
User Guide
Ensuring the Physical Layer Routes Your Data as Expected
Layer 1 routes data from the MAP, Auxiliary, and CPU interfaces to the outgoing
CPRI frame, and routes data from the CPRI frame to the MAP, Auxiliary, and CPU
interfaces. To ensure the data is routed as you intend, observe the following
guidelines:
■ To configure a CPRI IP core variation that supports only the AUX interface, in the
CPRI parameter editor, set the number of antenna-carrier interfaces to the value of
0.
■ To program a subset of the configured antenna-carrier channels as active
antenna-carrier channels, set the
map_ac field of the CPRI_MAP_CNT_CONFIG register
to the appropriate number of channels. Refer to “Number of Antenna-Carrier
Interfaces” on page 3–6 . The combination of CPRI line rate, MAP interface sample
width (programmed in the map_15bit_mode field of the CPRI_MAP_CONFIG register),
and sampling rate (programmed in the map_n_ac field of the CPRI_MAP_CNT_CONFIG
register) restricts the number of active antenna-carrier interfaces your CPRI IP core
can support without data corruption. Refer to
Table 4–5 and Table 4–6 on
page 4–17 . Programming these register fields affects how your AxC samples are
packed in the data channels. You can program these register fields, and they have
the same effect on the MAP interface, whether or not your CPRI IP core variation
uses the AUX interface.
■ If your CPRI IP core variation and application support both an AUX interface and
a MAP interface, use the
cpri_tx_aux_mask mask signal (bits [31:0] of the
aux_tx_mask_data[64:0] bus described in Table 6–4 on page 6–7 ) to override the
MAP interface (data) and CPU interface (control words) write access to the CPRI
frame data per data bit. The mask signal is a MUX select. Setting a bit in the mask
ensures the corresponding data bit inserted in the outgoing CPRI frame is data
from the AUX interface. Resetting a bit in the mask ensures the corresponding bit
inserted in the outgoing CPRI frame is data from the MAP interface or control
words from the CPU interface.
■ The AUX interface routes raw data. It passes control words unexamined as if they
were data. Your application can separate the control and data words in the AUX
stream if your application requires that they be separated.
■ When the source of the data for the CPRI frame is not the AUX interface, you must
ensure you deassert the bits in
cpri_tx_aux_mask to prevent AUX data from being
inserted in the outgoing CPRI frame.
Receiver
The receiver in the low-level interface receives the input from the CPRI link, and
performs the following tasks:
■ Converts the data to the main clock domain
■ Performs CPRI frame detection
■ Separates data and control words
■ Descrambles data at 4915.2 Mbps, 6144.0, and 9830.4 Mbps CPRI line rates
(optional)