Ethernet Design Example Components User Guide

ID 683044
Date 9/27/2021
Public

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2.4.1. Sampling Clock Frequency

To achieve the recommended frequency for the sampling clock, follow these steps:

  1. The SYNC_MODE and SAMPLE_SIZE parameters determine the sampling clock factor, which is then used to determine the required PLL settings. Use the Table 18 to identify the sampling clock factor for your configuration.
  2. Use the sampling clock factor identified in the previous step to determine the PLL settings. Table 21 lists the settings for Stratix® V PLL Intel® FPGA IP.
  3. In the case where the sampling clock factor is not achievable using the current PLL, Intel recommends that you use an alternative sampling clock frequency of 80 MHz.
  4. Sampling clock granularity determines the accuracy of synchronization where smaller granularity gives better accuracy. Table 19 and Table 20 show the granularity for each recommended sampling clock.
Table 18.  Sampling Clock Factor
SYNC_MODE Reference Clock Frequency

(MHz)

Sampling Clock Factor
SAMPLE_SIZE = 64 SAMPLE_SIZE = 128 SAMPLE_SIZE = 256
0, 1 125 16/63 32/33 64/63
156.25 64/315 128/155 256/375
2 Master/slave frequency 64/63 128/153 256/375
3, 4 156.25 64/63 128/153 256/375
312.5 32/33 64/63 128/153
5, 6 125 32/63 64/63 128/63
312.5 64/315 128/155 256/375
7, 8 125 N/A N/A 32/13
390.625 N/A N/A 256/375
9, 10 156.25 32/33 64/31 128/63
390.625 64/155 128/185 256/375
11, 12 312.5 16/15 32/33 64/63
390.625 64/75 128/185 256/253
13 62.5 64/63 128/153 256/253
125 32/33 64/63 128/153
14 62.5 32/33 64/63 128/153
156.25 64/155 128/155 256/375
15 62.5 64/63 128/153 256/253
312.5 64/155 128/155 256/375
Table 19.  Sampling Clock Granularity for Sampling Clock FactorThe following is the sampling clock granularity for sampling clock factor in Table 18.
SYNC_MODE Reference Clock Frequency

(MHz)

Sampling Clock Granularity (ns)
SAMPLE_SIZE = 64 SAMPLE_SIZE = 128 SAMPLE_SIZE = 256
0, 1 125 0.5 0.25 0.125
156.25
2 Master/slave frequency Ref clock period/64 Ref clock period/128 Ref clock period/256
3, 4 156.25 0.1 0.05 0.025
312.5
5, 6 125 0.25 0.125 0.0625
312.5
7, 8 125 N/A N/A 0.25
390.625
9, 10 156.25 0.2 0.1 0.05
390.625
11, 12 312.5 0.2 0.1 0.05
390.625
13 62.5 0.25 0.125 0.0625
125
14 62.5 0.5 0.25 0.125
156.25
15 62.5 0.25 0.125 0.0625
312.5
Table 20.  Sampling Clock Granularity Using 80 MHz Sampling Clock
SYNC_MODE Time of Day Frequency

(MHz)

Sampling Clock Granularity (ns)
SAMPLE_SIZE = 64 SAMPLE_SIZE = 128 SAMPLE_SIZE = 256
0, 1 125 0.5 0.5 0.5
156.25
2 62.5 0.5 0.5 0.5
125 0.5 0.5 0.5
156.25 0.1 0.1 0.1
312.5 0.1 0.1 0.1
390.625 N/A 0.02 0.02
402.83 N/A N/A N/A
3, 4 156.25 0.1 0.1 0.1
312.5
5, 6 125 0.5 0.5 0.5
312.5
7, 8 125 N/A 0.5 0.5
390.625
9, 10 156.25 N/A 0.1 0.1
390.625
11, 12 312.5 N/A 0.1 0.1
390.625
13 62.5 0.5 0.5 0.5
125
14 62.5 0.5 0.5 0.5
156.25
15 62.5 0.5 0.5 0.5
312.5
Table 21.  PLL Settings for Stratix® V Devices
Sampling Clock Factor PLL Counter
M N C
16/15 16 5 3
16/63 16 3 21
32/13 32 13 1
32/33 32 3 11
32 11 3
32/63 32 3 21
64/31 64 31 1
64/63 64 9 7
64 21 3
64/75 64 25 3
64/155 64 31 5
64/315 64 21 15
128/63 128 21 3
128/153 128 51 3
128 17 9
128 9 17
128/155 128 31 5
128/185 128 37 5
256/253 256 11 23
256/375 256 75 5
  256 25 15