LSM6DSV16X MLC — tag 0x1B (IIR filter) never reaches FIFO despite MLC_FILTER_FEATURE_FIFO_EN=1

[NullPointerMaybe]

I am using LSM6DSV16X with MLC configured in MEMS Studio v2.3.1. 

The MLC has an IIR2 high-pass filter on accelerometer XYZ with "store in FIFO" enabled. The UCF was generated by the MLC Tool (internal version 2.4.4 as reported in the output JSON).

 

Expected: IIR filter output values appear in FIFO as tag 0x1B frames, as declared in the mlc_identifiers section of the generated JSON.

 

Observed: Tag 0x1B frames never appear in the FIFO. Firmware drains the FIFO after each 60-sample window and observes exactly 3 MLC words per window — 2x tag 0x1C (features) and 1x tag 0x1A (result). No tag 0x1B words arrive.

 

Verified:

- EMB_FUNC_FIFO_EN_B (0x45) = 0x02, MLC_FILTER_FEATURE_FIFO_EN bit is set (confirmed against DS13510 Section 13.18)

- mlc.json correctly lists fifo_tag 0x1B identifiers (FILTER_HP_ACC_X/Y/Z) in the metadata

- mlc_settings.json has "input": "Acc_XYZ + store in FIFO" for the filter

- Firmware FIFO drain handles tag 0x1B explicitly — not dropped in software

- No unknown FIFO tag warnings in serial log

 

Question: Is tag 0x1B FIFO output for IIR filter data functional for LSM6DSV16X in the current MLC Tool? If so, what additional configuration or register setting is required beyond MLC_FILTER_FEATURE_FIFO_EN=1 to make the compiled MLC binary emit filter values to the FIFO?

[Federica Bossi]

Hi ​@NullPointerMaybe ,

You are right tag 0x1B is intended for MLC filter FIFO output on LSM6DSV16X. Please consider that enabling only MLC_FILTER_FEATURE_FIFO_EN is not sufficient for filter outputs. In addition to the global FIFO enable bits, each individual filter must also be enabled at configuration-generation level by adding:

-MLC_enable_filters_in_FIFO

 

in the custom options under “Config generation” using the “...” button into MLC page.
Also note that MLC result entries are written to FIFO only when the class changes.