nSTATUS is sometimes asserted low during Agilex-F configuration when operating in PMBus slave mode

Hi Itzik,

Thank you for sharing the details. Based on Agilex 7 guidelines, this issue is typically related to configuration handshake or PMBus timing.
Key checks:

1. nCONFIG/nSTATUS sequence
For Avalon‑ST x16 mode, hold nCONFIG low until nSTATUS goes low, then drive nCONFIG high. Only start sending AVST data after nSTATUS is high and AVST_READY asserts. Keep AVST_CLK free‑running.

2. Power‑up and POR
Ensure rails ramp in the correct order (Group 1 → Group 2 → Group 3) and meet POR/tRAMP requirements. If POR timing is violated, configuration can fail and nSTATUS may drop.

3. PMBus slave flow
PMBus pins are undefined until the device is fully powered. The external PMBus master must:

• Poll PWRMGT_ALERT at ≤100 ms intervals.
• Start ARA only after ALERT asserts.
• Send VOUT_COMMAND within 200 ms of ALERT.
  Sending commands too early or missing this window can cause SDM errors and nSTATUS low.

Why retry works:
After the first failure, rails and clocks are stable and the SDM resets cleanly, so the next attempt succeeds.

Recommended actions:

• Verify nCONFIG/nSTATUS handshake and AVST_READY timing.
• Confirm power‑up sequence and POR timing.
• Check PMBus master flow for ALERT polling and VOUT_COMMAND timing.
• If failure repeats, read STATUS_BYTE to identify PMBus or regulator errors.

Please refer to Agilex™ 7 Power Management User Guide

Regards
Fakhrul