Altera CPRI IP Core - Manual (Page 76)

4–44 Chapter 4: Functional Description
CPU Interface
CPRI MegaCore Function December 2013 Altera Corporation
User Guide
access the full control word when the CPRI line rate is 9.8304 Gbps, or from zero to
two when the CPRI line rate is 6.144 Gbps, for example. Refer to
“Control Word
Retrieval Example” on page 4–47 for an example.
Table 4–14 shows the positions of the control word bytes in CPRI_RX_CTRL[31:0] . Each
control word nibble appears in the table as 0xF. For example, at the CPRI line rate of
614.4 Mbps, when you access control receive table entry X by reading from the
CPRI_RX_CTRL register, the 8-bit control word from hyperframe position #Z.X.0 is in
bits [31:24] of the register. At the CPRI line rate of 1228.8 Mbps, the byte from position
#Z.X.0.0 is in bits [31:24] of the register, and the byte from position #Z.X.0.1 is in bits
[23:16] of the register. At the CPRI line rate of 3072.0 Mbps, when you access a control
receive table entry by reading from the
CPRI_RX_CTRL register, you must read twice. In
the first read, you access the 32 bits of the control word from positions #Z.X.0.0 (in
register bits [31:24]), #Z.X.0.1 (in register bits [23:16], #Z.X.0.2 (in register bits [15:8]),
and #Z.X.0.3 (in register bits [7:0]). In the second read, you access the eight bits of the
control word from position #Z.X.0.4 in bits [31:24] of the register.
Writing the Outgoing Control Words
A control transmit table contains an entry for each of the 256 control words in the
current hyperframe. Each control transmit table entry contains a control word and an
enable bit. As the frame is created, if a control word entry is enabled, and the global
tx_ctrl_insert_en bit in the CPRI_CONFIG register is set, the low-level transmitter
writes the appropriate control transmit table entry to the CPRI frame’s control word.
You write to a control transmit table entry through the CPRI_TX_CTRL register. This
register access method requires that you write the control word in 32-bit sections. Use
the
cpri_ctrl_position field of the CPRI_CTRL_INDEX register to specify the 32-bit
section you are currently writing to the CPRI_TX_CTRL register. Table 4–14 applies to
the CPRI_TX_CTRL register as well as the CPRI_RX_CTRL register. Refer to Table 4–14 for
control word byte location in the CPRI_TX_CTRL register and how to use the
cpri_ctrl_position field.
To write a control word in the control transmit table, perform the following steps:
1. Write the control word number X to the cpri_ctrl_index field of the
CPRI_CTRL_INDEX register.
2. Reset the cpri_ctrl_position field of the CPRI_CTRL_INDEX register to the value of
zero.
3. Write the first 32-bit section of the next intended #Z.X control word to the
CPRI_TX_CTRL register, as shown in Table 4–14 .
Table 4–14. Control Word Byte Positions in CPRI_RX_CTRL Register
cpri_ctrl_position
CPRI Line Rate (Mbps)
614.4 1228.8 2457.6 3072.0 4915.2 6144.0 9830.4
0 FF000000 FFFF0000 FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF
1 0 0 0 FF000000 FFFFFFFF FFFFFFFF FFFFFFFF
2 0 0 0 0 0 FFFF0000 FFFFFFFF
3 0 0 0 0 0 0 FFFFFFFF