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

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