Altera CPRI IP Core - Manual (Page 204)

E–26 Appendix E: Delay Measurement and Calibration
Single-Hop Delay Measurement
CPRI MegaCore Function December 2013 Altera Corporation
User Guide
To calculate the round-trip cable delay in this system, perform the steps in
“Round-Trip and Cable Delay Calculation Example 1: Two Stratix IV GX Devices” ,
replacing values according to Table E–11 . The final row of Table E–11 shows the
calculated cable delay.
Table E–11. Example 4 Data and Calculations
Calculation
Component
Delay Component Relevant Register Value or Source Table Delay
Total
(decimal)
Round trip delay rx_round_trip_delay = 0x6D 109
REC Tx path delay
T_T4 Table E–6 on page E–14 6.5
16.1
Tx buffer delay tx_ex_buf_delay = 0x33A 6.50
T_txv_TX
tx_bitslipboundaryselect = 0x0
Table E–7 on page E–16
3.1
REC Rx path delay
T_txv_RX
rx_bitslipboundaryselectout = 0x2
Table E–1 on page E–5
5.65
44.23
Rx buffer delay rx_ex_buf_delay = 0xF2C 30.58
Calibration pointer cal_pointer = 3 3
Byte alignment rx_byte_delay = 0 0
T_R1 Table E–3 on page E–8 5
T14 (Round trip delay minus REC Tx path delay minus REC Rx path delay) 48.67
RE Tx path delay
T_T4 Table E–6 on page E–14 7
19.79
Tx buffer delay tx_ex_buf_delay = 0x46B 8.94
T_txv_TX
tx_bitslipboundaryselect = 0xA
(decimal 10)
Table E–7 on page E–16
3.85
RE Rx path delay
T_txv_RX
rx_bitslipboundaryselectout = 0x7
Table E–1 on page E–5
7.025
27.025
Rx buffer delay rx_ex_buf_delay = 0x5F4 12
Calibration pointer cal_pointer = 3 3
Byte alignment rx_byte_delay = 0 0
T_R1 Table E–3 on page E–8 5
Loopback delay on RE slave 1
Toffset (RE Tx path delay + RE Rx path delay + loopback delay) 47.815
Cable delay (T14 minus Toffset) 0.855