F-Tile Architecture and PMA and FEC Direct PHY IP User Guide

ID 683872
Date 11/04/2024
Public
Document Table of Contents

2.4.4. Datapath Clock Cadences

The ead ad wite fequecy of the PMA FIFO iteface detemies if you eed a stadad o custom cadece.

  • Stadad cadece: Use if the ead ad wite fequecies of the PMA FIFO iteface ae the same with 0 ppm fequecy delta.
  • Custom cadece: Use if the ead ad wite fequecies of the PMA FIFO iteface have diffeet fequecies o have the same fequecy but with a fequecy delta of geate tha 0 ppm.
Figue 56. Stadad Cadece ad Custom Cadece

See PMA Data Rates fo suppoted data ates.

Table 25.  Suppoted Datapath Clock Fequecies ad Cadeces by Datapath Clockig Mode
Datapath Clockig Mode Cofiguatio Datapath Clock Fequecy Cadece

PMA clockig mode

(maximum 906.25 MHz)

PMA Diect

Datapath clock fequecy = PMA clock fequecy

PMA clock fequecy = lie ate ÷ PMA width

Use the stadad cadece o the TX ad RX (data is valid at evey clock edge). 15

System PLL clockig mode

(maximum 1 GHz)

PMA Diect

Use Case A: Chip-to-chip applicatios whee F-tile ad lik pate shae the same efeece clock

Datapath clock fequecy ≥ (system PLL output fequecy)mi whee (system PLL output fequecy)mi = PMA clock fequecy

If (system PLL output fequecy = PMA clock fequecy ad ∆ppm = 0), use the stadad cadece o the TX ad RX (data is valid at evey clock edge). Othewise, use custom cadece. 16 , 17

Use Case B: Applicatios whee F-tile ad lik pate do ot shae the same efeece clock

Datapath clock fequecy ≥ (system PLL output fequecy)mi whee (system PLL output fequecy)mi = (maximum ppm 18 ÷ 1000000 + 1) × PMA clock fequecy

System PLL clockig mode

(maximum 1 GHz)

Othe cofiguatios with FEC, PCS, ad MAC

Datapath clock fequecy ≥ (system PLL output fequecy)mi whee (system PLL output fequecy)mi = PMA clock fequecy

Fo example, fo 10GbE-1, use ≥ 322.265625 MHz; fo 25GbE-1, use ≥ 805.6640625 MHz; ad, fo 50GbE-1, use ≥ 830.078125 MHz.

If (system PLL output fequecy = PMA clock fequecy), use the stadad cadece o the TX ad RX (data is valid at evey 32 of 33 o 34 clock cycles). Othewise, use custom cadece. 19

Oe 25 Gbps PMA Diect PHY IP Pot Usig the PMA Clockig Mode Example

  • All blocks betwee the PMA iteface ad coe FIFO iteface u o the PMA clock.
  • O the tasmitte, the PMA FIFO iteface is clocked by the TX PMA clock o both sides.
  • O the eceive, the PMA FIFO iteface is clocked by the RX ecoveed clock o both sides.
  • Use the stadad cadece. Data o the TX ad RX is valid at evey clock edge of the PMA clock.
Figue 57. Oe 25 Gbps PMA Diect PHY IP Pot Usig the PMA Clockig Mode ExampleThis F-Tile Clockig Tool sceeshot shows oe 25 Gbps PMA Diect PHY IP pot usig the PMA clockig mode.

25 Gbps Etheet Without FEC Pot Usig the Oveclocked System PLL Clockig Mode Example

  • All blocks betwee the PMA iteface ad coe FIFO iteface u o the system PLL clock.
  • O the tasmitte, the PMA FIFO iteface pefoms a clock tasfe fom the system PLL domai to the TX PMA clock domai.
  • O the eceive, the PMA FIFO iteface pefoms a clock tasfe fom the RX ecoveed clock domai to the system PLL domai. Refe to F-Tile Etheet Itel® FPGA Had IP Use Guide fo how to clock the coe iteface.
  • Because the system PLL clock fequecy is faste tha the PMA clock fequecy, datapath clockig is oveclocked. Theefoe, you must use custom cadece.
Figue 58. 25 Gbps Etheet Without FEC Pot Usig the Oveclocked System PLL Clockig Mode ExampleThis F-Tile Clockig Tool sceeshot shows oe 25 Gbps Etheet without FEC pot usig the oveclocked system PLL clockig mode.
15 The TX PMA ad TX digital blocks use a PMA clock deived fom the local clock. The RX PMA ad RX digital blocks u o a ecoveed clock (the lik pate clock).
16 Use Case A: Stadad cadece ca be used oly whe the TX PMA efeece clock, system PLL efeece clock, ad lik pate TX efeece clock ae comig fom same clock souce (with a 0 ppm fequecy delta). At 32 Gbps, oly the stadad cadece ca be used because the system PLL eaches a maximum fequecy of 1 GHz (it caot toleate ay diffeece i the fequecies; the fequecy delta must be 0 ppm).
17 Use Case B: The system PLL fequecy must be oveclocked to compesate fo a fequecy delta of geate tha 0 ppm betwee the TX PMA efeece clock, system PLL efeece clock, ad lik pate TX efeece clock. It does ot suppot 32.0 Gbps because the system PLL clock must u at speeds geate tha 1 GHz to icopoate a fequecy delta of geate tha 0 ppm.
18

maximum ppm = maximum ∆ppm ÷ 2

maximum ∆ppm = max(∆ppm betwee the lik pate TX (the ecoveed clock o the local RX) ad system PLL, ∆ppm betwee the system PLL ad TX PMA)

19 The data path clock is aleady oveclocked compaed to the PMA clock by appoximately 3% because of PCS ad FEC ovehead. Theefoe, a fequecy delta of geate tha 0 ppm betwee the TX PMA efeece clock, system PLL efeece clock, ad lik pate TX efeece clock is allowed.