Forum Discussion

pryngshu's avatar
pryngshu
Icon for New Member rankNew Member
21 hours ago

Unable to Generate Valid PAM4 Eye Diagram and BER Measurements on Stratix 10 SI E-Tile Native PHY

Hardware

  • Intel Stratix 10 Development Kit
  • E-Tile Native PHY IP
  • Single SMA TX and RX channel
  • SMA-to-SMA cable (50 Ω)

Software

  • Quartus Prime Pro 18.1
  • Intel Transceiver Toolkit

Configuration

  • PAM4 operation
  • Line rate: 51 Gbps
  • One TX channel connected directly to one RX channel through an SMA cable
  • Design compiles successfully and programming is successful.

Problems Encountered

1. PAM4 Eye Detection Failure

Transceiver Toolkit reports:

"PAM4 eye could not be detected, check lock status and run RX adaptation."

2. RX Adaptation Questions

One-time adaptation completes successfully, but:

  • Eye detection still fails.
  • BER measurements do not produce a usable eye diagram.

Questions:

  • Should continuous adaptation be used instead?
  • Is there a recommended adaptation sequence before running Eye Viewer?

3. Eye Diagram Parameters Undefined

After running Eye Viewer:

  • Eye Width = Undefined 
  • Eye Height = Undefined
  • i.e. ratio = (0/0)
  • The heatmap returns with full RED and no eye diagram.

The eye diagram is not generated even though the receiver reports lock.

4. BER Test Issues

I am unsure:

  • How many bits are required before Eye Viewer can successfully generate a PAM4 heat map.
  • Whether there is a minimum BER sample count required for a valid eye diagram at 51 Gbps.
  • Whether insufficient captured bits can cause "Undefined" eye width/height.

5. TX Pattern

Currently transmitting a repeating user-defined pattern, for example:

.tx_parallel_data({20{40'b0, 40'h0F0F0F0F0F, 40'b0, 40'h0F0F0F0F0F}})

Questions:

  • Is this pattern suitable for PAM4 eye measurements?
  • Would PRBS13 or PRBS31 be required instead?

6. Signal Integrity

Questions:

  • Can a 50 cm SMA cable (Pasterneck PE3CA1035) reliably carry a 51 Gbps PAM4 signal?
  • Is additional equalization or TX pre-emphasis typically required even for short SMA connections?

7. Transceiver Toolkit Configuration

I would appreciate guidance on:

  • Recommended Eye Viewer settings.
  • Auto Sweep configuration.
  • Vertical and horizontal ranges.
  • TX FIR tap values.
  • RX CTLE/DFE settings.
  • Required number of bits before starting the eye scan.

 

  1. What are the common reasons for "PAM4 eye could not be detected" despite PLL/CDR lock?
  2. What checks should be performed before running Eye Viewer?
  3. PRBS as well as USER sequence, both generate complete RED heatmap, why?
  4. How many bits should be accumulated before generating an eye diagram at 51 Gbps?
  5. Are there recommended TX FIR, CTLE, and DFE settings for a direct SMA-to-SMA connection?
  6. Has anyone successfully generated a PAM4 eye using the Stratix 10 E-Tile Native PHY over SMA? If so, could you share the required configuration or debugging steps?
Configuration
Programmable Logic Device
quality|reliability

1 Reply

  • Ash_R_Altera's avatar
    Ash_R_Altera
    Icon for Regular Contributor rankRegular Contributor
    1 hour ago

    Hi,

    Here are my recommendations:

    Step 1 — Upgrade Quartus Prime Pro (Critical)

    Quartus 18.1 is 8 years old. PAM4 E-Tile support has received extensive fixes since then. Recommend upgrading to at least Quartus 24.x (or latest). Many PAM4 adaptation, eye viewer, and toolkit fixes were delivered in 19.x–24.x releases.

    Step 2 — Use Proper PRBS Pattern for PAM4

    The user-defined pattern does NOT exercise all 4 PAM4 voltage levels. This alone can cause "eye could not be detected."

    Use PRBS31Q (quaternary/PAM4-aware PRBS) from the Transceiver Toolkit's built-in pattern generator, not a custom pattern. This ensures all 4 symbol levels (0, 1, 2, 3) are properly exercised.

    Step 3 — Signal Integrity Check (SMA Cable)

    A 50 cm Pasternack PE3CA1035 SMA cable may have excessive insertion loss at 25.5 GHz (PAM4 Nyquist for 51 Gbps). Recommend:

    Use the shortest possible cable (< 15 cm) or a calibrated test fixture

    Alternatively, test with serial internal loopback (SILB) first to eliminate the cable as a variable

    Step 4 — Adaptation Sequence

    Run continuous adaptation (not one-time) for PAM4. The adaptation FSM needs to converge VGA/AGC, CTLE, DFE, and IQ timing for all 3 PAM4 eyes.

    After enabling continuous adaptation, wait for it to fully converge (observe stable CTLE/DFE tap values in Toolkit) before running Eye Viewer.

    Step 5 — TX Pre-emphasis / FIR Settings

    For a short SMA loopback, start with:

    Pre-tap = 0, Main tap = max (e.g., 55), Post-tap = 0

    Adjust only if needed after confirming basic link with SILB

    Step 6 — Eye Viewer Configuration

    Ensure Eye Viewer is set to PAM4 mode (measures top, middle, and bottom eyes)

    Let the tool accumulate sufficient bits at each BER point (~10⁸ bits minimum at 51 Gbps before starting eye scan)

    Verify CDR lock-to-data is asserted before running Eye Viewer

    Step 7 — Verify lock status registers

    Before running Eye Viewer, confirm: rx_is_lockedtodata = 1 and rx_pll_locked = 1

    If CDR is locked to reference (not data), the eye measurement will fail

     

    Recommended Debug Sequence (Short form for response)

    First: Try internal serial loopback with PRBS31Q → confirms transceiver PMA works

    If SILB passes: try external loopback with shortest cable available

    If short cable passes: troubleshoot with original 50 cm cable (likely too lossy)

     

    Regards