Altera CPRI v6.0 MegaCore Function - Manual (Page 68)

Specifying the Position in the Control Word
You can access only 32 bits in a single register access. Depending on the CPRI line bit rate, a control word
may have multiple 32-bit sections. Therefore, in addition to specifying the control word location in the
CPRI frame, you must also specify a 32-bit aligned position in the control word.
Table 3-13: Control Word Byte Positions in RX_CTRL and TX_CTRL Registers
In this table, each control word nibble is indicated with 0xF. The presence of 0xF or 0x0 indicates whether the
nibble within the register is populated with a valid control word nibble.
CPRI Bit Rate (Gbps)
Register Access Sequence Number ({rx,tx}_ctrl_seq)
0
(first access)
1
(2nd access)
2
(3rd access)
3
4th access)
4
(5th access)
0.6144 FF000000 0 0 0 0
1.2288 FFFF0000 0 0 0 0
2.4576 FFFFFFFF 0 0 0 0
3.072 FFFFFFFF FF000000 0 0 0
4.9152 FFFFFFFF FFFFFFFF 0 0 0
6.144 FFFFFFFF FFFFFFFF FFFF0000 0 0
9.8034 FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF 0
10.1376 FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FF000000
However, the table does not clarify which control word byte occupies which position in the register. The
following examples indicate the correspondence between register bytes and control word bytes:
• At the CPRI line bit rate of 0.6144 Gbps, when you access hyperframe control word X, the 8-bit control
word from hyperframe position #Z.X.0 is in bits [31:24] of the register.
• At the CPRI line bit rate of 1.2288 Gbps, 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 bit rate of 3.072 Gbps, you must access the register twice to retrieve or write the full
control word. In the first access operation, you access the 32 bits of the control word in 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 access operation, you access the eight bits of the control
word in position #Z.X.0.4 in bits [31:24] of the register.
Retrieving the Hyperframe Control Words
A control receive table contains one entry for each of the 256 control words in the current hyperframe. To
read a control word, your application must write the control word number X to the
rx_ctrl_x
field of the
CTRL_INDEX
register and then read the last received #Z.X control word from the
RX_CTRL
register. Because
the register can hold only 32 bits at a time, depending on the CPRI line bit rate, reading the full control
word may require multiple register accesses. Increment the value in the
rx_ctrl_seq
field of the
CTRL_INDEX
register from zero to four to access the full control word when the CPRI line bit rate is
10.1376 Gbps, or from zero to two when the CPRi line bit rate is 6.144 Gbps, for example.
3-38 Specifying the Position in the Control Word
UG-01156
2014.08.18
Altera Corporation Functional Description
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