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

ID 683872
Date 1/24/2025
Public

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3.3.1.2. FGT PMA Configuration Rules for GPON Mode

You can implement the upstream GPON, XG(S)PON, 25G PON, and 50G asymmetric PON protocols with the F-Tile PMA/FEC Direct PHY Intel® FPGA IP by using the settings shown below:
  • Set the FGT PMA configuration rules parameter to GPON.
  • Set the Adaptation mode parameter to manual.
  • Enable the fgt_rx_cdr_fast_freeze_sel port.
  • Enable the fgt_rx_cdr_freeze port.

To achieve the best FGT RX performance when receiving the burst mode traffic, you must adhere to the following guidelines:

  • You must make sure that addresses 0x62000[16] and 0x62004[12] are set to 1’b1.
    Note: 0x62000 and 0x62004 are the offset addresses for lane 0.
  • You must tie the fgt_rx_cdr_fast_freeze_sel signal to 1’b0.
  • You must assert the fgt_rx_cdr_freeze signal when the burst disappears and deassert fgt_rx_cdr_freeze when the burst appears. For the timing relationship between the fgt_rx_cdr_freeze signal and bursts, refer to the following conditions:
    • The transceiver input signal fgt_rx_cdr_freeze propagates to *ingress*231* with a latency about 10 ns.
    • *ingress*231* is the internal signal that controls the CDR freeze or unfreeze logic.
    • It is recommended that you align *ingress*231* signal assertion and deassertion with the rx_serial_data disappearing and reappearing.
    • You can capture the *ingress*231* signal using Signal Tap via the path *__tiles|z*_x*_y*_n*__reset_controller|x_f_tile_soft_reset_ctlr_sip_v1|x_ftile_reset|rst_ctrl|iflux_ingress_direct_231
Table 30.  Timing Impact of *ingress*231* and rx_serial_data
Signal Condition Early Late
Assertion of *ingress*231* The CDR may not track the tail of the prior data resulting in higher BER. The CDR can drift in frequency resulting in a longer lock time on the next burst.
Deassertion of *ingress*231* The CDR can drift in frequency resulting in a longer lock time on the next burst. The start of the preamble can be missed resulting in a longer lock time on the current burst.
Note: It is acceptable if you cannot perfectly align the *ingress*231* signal with the rx_serial_data. The FGT RX CDR can lock to the incoming burst fast enough within the preamble duration to meet the PON-related specifications.
  • During the idle time (no active burst), the differential voltage at the FGT RX should be 0 instead of a negative value. This is to ensure the AC coupling capacitor can quickly charge up to a stable value when the burst arrives.
    • If an optical line terminal (OLT) optical module is connected to FGT RX, then the enabled squelch on the optical module should meet the 0 differential voltage requirement of the FGT RX.
    • If the FGT TX is connected to FGT RX, then enable TX electrical idle to meet the 0 differential voltage requirement. For PON applications with 32-bit PMA width:
      • To enable TX electrical idle: set the tx_parallel_data bit[35] and bit[75] to 1’b1
      • To disable TX electrical idle: set the tx_parallel_data bit[35] and bit[75] to 1’b0
  • You must manually tune the RX EQ parameters: VGA gain, high frequency boost and DFE data tap 1.
    Note: When the other parameters are fixed, a smaller RX input voltage swing requires a smaller VGA gain value. A larger RX input voltage swing requires a larger VGA gain value.
  • You may need to manually tune the CDR gain parameters: proportional gain and integral gain, if the tuned RX EQ parameters cannot achieve the performance you require.
    • When the fgt_rx_cdr_freeze signal asserts, the integral path is frozen while the proportional path is still active.
    • Higher gain value for the proportional path and integral path helps the RX CDR to realign to the incoming data phase quicker but can create a higher jitter in the process.
    • When the fgt_rx_cdr_freeze signal asserts, a higher gain value for the proportional path may speed up the drifting process and cause the CDR to be far away from the target phase alignment.
    • Proportional gain register is: 0x4157C[24:20].
      Note: This is the offset address for lane 0.
    • Integral gain registers are: 0x4158C[17:13], 0x41484[14:10], 0x41484[24:20], 0x41488[4:0], 0x41488[14:10], 0x41488[24:20], 0x4148C[4:0], 0x4148C[14:10]
      Note: These are the offset addresses for lane 0.
    • An example of optimal settings for the CDR gain registers are:
      • Proportional gain value: 0xA
      • Integral gain value: 0xC
To use the LTR mode when you select the GPON setting for the FGT PMA configuration rules parameter, you must adhere to the following guidelines:
  • Set the Enable fgt_rx_cdr_set_locktoref port parameter to On.
  • Set the CDR lock mode parameter to auto.
  • Set registers 0x41678[27:26] and 0x41678[29:28] to 2'b11, otherwise, the LTR/LTD switching may fail.
  • Set registers 0x41580[30] and 0x41580[31] to 1'b1, otherwise, during LTR mode, the rx_parallel_data may be invalid.