SJA1110: Packet forwarding stops after writing L2 Lookup Table entry via SPI

HeeSu — Thu, 22 Jan 2026 02:03:25 GMT

Hello,

I am experiencing an issue with SJA1110 switch where packet forwarding stops after writing L2 Lookup Table entries via SPI.

Environment:

Symptom:

State Packet Forwarding

Before writing L2 entry	Works (PTP, ping, UDP)
After writing L2 entry	Stops completely

Observations:

I wrote L2 Lookup Table entries through a custom Python script that keeps the FTDI channel open continuously for switch management
When reading back with the provided L2 Lookup Table read script (specifying index range 0-1024), the written entries are visible
However, when using the provided switch table dump script, only the entries defined in the ELF configuration file are shown
The written entry can be read back correctly, but packet forwarding does not work

Questions:

Why do the L2 Lookup Table read script and the switch table dump script return different results? Is there a difference between static and dynamic entry areas in the L2 Lookup Table?
Does writing an L2 Lookup Table entry affect other internal switch state? (e.g., hash table, learning database, forwarding behavior) What could cause packet forwarding to stop even though the entry appears to be written correctly?

Re: SJA1110: Packet forwarding stops after writing L2 Lookup Table entry via SPI

PavelL — Thu, 22 Jan 2026 13:59:29 GMT

Hello @HeeSu ,

Thank you for the details. But I still miss a few specifics to move this query forward.

Clarifications needed:

“L2 Lookup Table read script” — do you mean read_l2_lookup_table.py from sja1110evm_hosttools_v1.2 (runtime read over SPI)?
“Switch table dump script” — which exact tool/script is this?

Please share:

Your switch configuration (ELF/HEX or project (MEX file)) and the custom Python scripts you used. For successful upload of python scripts, you need to rename python scripts to .txt .
Console output/logs from both scripts.
Runtime L2 table snapshots (index 0…1024) before/after the write that triggers the issue, plus the DYN_BE_LKP_CTRL register readout before/after (to confirm the write sequence completed).

If you prefer to proceed privately, you can open a support ticket here:
https://support.nxp.com/s/?language=en_US

Best regards,

Pavel