Altera CPRI IP Core - Manual (Page 206)

E–28 Appendix E: Delay Measurement and Calibration
Multi-Hop Delay Measurement
CPRI MegaCore Function December 2013 Altera Corporation
User Guide
Two-Hop Round-Trip and Cable Delay Calculation Example
This section walks through an example calculation for the system shown in
Figure E–8 .
In the example, all of the four CPRI IP cores are configured with autorate negotiation
enabled and are running at CPRI data rate 3.072 Gbps.
Example calculations for the first hop appear in “Round-Trip and Cable Delay
Calculation Example 3: Two Different Device Families” on page E–24 . Example
calculations for the second hop appear in “Round-Trip and Cable Delay Calculation
Example 2: Two Arria II GX Devices” on page E–23 .
Assuming the multihop system has the same register values as in these two
single-hop examples, you calculate the multihop round-trip delay and total cable
delay as follows:
Round-trip delay =  rx_round_trip_delay (hop i) +  (TBdelayUL + TBdelayDL)(j)
– n
= (105 + 132) + TBdelayUL + TBdelayDL – 1
= 236 cpri_clkout cycles + TBdelayUL + TBdelayDL
Total round-trip CPRI-link cable delay = 0.590944882 + 0.819488189
= 1.401433071 cpri_clkout cycles
The CPRI IP core does not provide a mechanism to measure the delays through the
external routing layer.
Figure E–8. Two-Hop System for Multihop Delay Calculation Example
RE Slave
REC Master
T12
optical link
optical link optical link
cpri_rx_rfp cpri_tx_rfp
cpri_rx_rfp cpri_tx_sync_rfp
T_txv_RX T_R1
T_T4
T_T4
TBdelay DL
T_R1
T_txv_TX
T_txv_TX
SAPs
T_txv_RX
T14
T34
Transceiver
and SFP
Transceiver
and SFP
R4
R1
AUX IF
R2
R3
RE Slave
RE Master
T12
optical link
cpri_rx_rfp cpri_tx_rfp
cpri_rx_rfp
T_txv_RX T_R1
T_T4
T_T4
T_R1
T_txv_TX
T_txv_TX
AUX IF
T_txv_RX
T14
T34
Transceiver
and SFP
Transceiver
and SFP
R4
R1
Toffset
SAPs
R2
R3
Routing Layer
TBdelay UL
Stratix IV GX device Arria II GX device Arria II GX device
Toffset