NXP MCXA344 Dual-Track Inductive Encoder

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Reference firmware and host dashboard for an HW_V2 dual-track inductive absolute encoder built around the NXP MCXA34x/MCXA344 device family. The firmware decodes 16/15 Vernier tracks into a single-turn absolute angle, accumulates multi-turn motion in RAM, and exposes live data through FreeMASTER.

Features

• 16/15 Vernier single-turn absolute angle solver with 16-bit output counts
• Heydemann-style ellipse correction for each (sin, cos) track
• Type-II software PLL for filtered angle and angular velocity
• Output-layer dead-band / hysteresis: 0.015 deg angle threshold and 1 count threshold
• Runtime magnitude monitoring and AGC trim after valid NVM calibration is loaded
• RAM-only signed multi-turn counter with host reset command
• FreeMASTER TSA variables plus a web dashboard and desktop .pmpx project
• DWT CYCCNT profiling for encoder_process() and total ADC ISR callback time

Hardware

Item	Value
MCU family	NXP MCXA34x / MCXA344 firmware target
Current Keil target note	ind_encoder.uvprojx is configured with MCXA343VLH / NXP.MCXA343_DFP.25.09.00, while source defines use CPU_MCXA344VLL and MCXA344_SERIES
Core clock	Cortex-M33 + FPU, 180 MHz firmware clock configuration
Analog front-end	MCXA OPAMP0/1 plus external TLV9062
ADC sampling	LPADC0/1, 4 raw channels, 10 kHz, CTIMER0 trigger, 8x hardware averaging
Host link	FreeMASTER over LPUART0, 115200 8N1, shared with debug console
Persistent calibration	Last 8 KB Flash area, 128-byte slots, monotonically selected sequence, CRC32 validation

Signal Wiring

Signal	Pin
A1 SIN	OPAMP0_OUT -> P2_15 (ADC0_A2)
A1 COS	OPAMP1_OUT -> P2_19 (ADC1_A2)
A2 SIN	TLV9062 external op-amp -> P2_6 (ADC1_A3)
A2 COS	TLV9062 external op-amp -> P2_7 (ADC0_A7)
FreeMASTER UART	LPUART0
Heartbeat LED	P3_11, toggles every 100 ms
ISR probe	P3_0, optional scope timing probe

Repository Layout

source/
  app_adc.{h,c}              CTIMER0-triggered LPADC sampling
  app_encoder.{h,c}          OS/HAL-independent encoder algorithm
  app_encoder_runtime.{h,c}  ADC callback, runtime trim, commands, snapshots, profiling
  app_encoder_storage.{h,c}  Flash calibration slot storage and CRC32 validation
  app_encoder_defaults.c     Board default calibration values
  app_freemaster.{h,c}       FreeMASTER init and TSA variable table
  hardware_init.{h,c}        OPAMP, pins, clock, debug UART
  main.c                     Boot entry and service loop

freemaster/
  index.html                 Web dashboard
  digital_encoder.pmpx       FreeMASTER desktop project
  simple-jsonrpc-js.js       JSON-RPC over WebSocket helper

doc/
  HW_V2.jpg                  HW_V2 hardware photo
  AN15044.pdf                Reference application note
  MCXA34x_based_Inductive_Encoder_v1.1.docx

Build and Flash

Open the Keil project directly or run the command-line build:

C:\Keil_v5\UV4\uVision.com -b ind_encoder.uvprojx -t ind_encoder -j0

Expected toolchain:

• Keil MDK with ARMCLANG V6.23
• NXP MCXA343 DFP 25.09.00 as currently referenced by the project file
• MCXA344-series SDK headers and source files already vendored in this repository

The project output name is ind_encoder. The scatter file reserves the final 8 KB of the 128 KB Flash image for factory calibration storage.

Calibration and Operation

First Factory Calibration

1. Connect the HW_V2 inductive encoder hardware and power the board.
2. Open freemaster/index.html or freemaster/digital_encoder.pmpx.
3. Connect FreeMASTER to LPUART0 at 115200 baud.
4. Press Factory Cal.
5. Rotate at least one complete mechanical revolution during the capture window.
6. Stop at the desired zero position. The last captured frame becomes factory zero.

The firmware captures 8192 decimated calibration samples, solves both track ellipse corrections, captures zero, writes one 128-byte calibration slot, and selects the highest valid sequence number on the next boot.

Runtime Commands

Command	Effect
Zero Here	Capture the current angle as a RAM zero offset; lost after reset
Reset Turns	Clear the RAM-only multi-turn counter
Factory Cal	Re-run factory calibration and persist it to Flash
MCU Reset	Trigger an NVIC system reset

FreeMASTER Dashboard

The dashboard reads TSA-exposed variables from the firmware:

• encoder_result.angle_deg, angle_counts, multi_turn_deg, and turn_count
• encoder_result.angular_velocity_dps
• encoder_result.mag16, mag15, mag16_raw, and mag15_raw
• encoder_result.status
• adc_result raw channels, sample count, and overrun count
• DWT profiler counters: encoder_perf_process_cycles, encoder_perf_isr_cycles, and peak values

Status bits are decoded by the dashboard into warning and fault states.

Bit	Name	Meaning
0x0001	NOT_CALIBRATED	No valid calibration is loaded
0x0002	TRACK16_WEAK	16-cycle track magnitude below the floor
0x0004	TRACK15_WEAK	15-cycle track magnitude below the floor
0x0008	ADC_RAIL	At least one ADC channel is clipped
0x0010	TRACK_MISMATCH	16/15 residual exceeds tolerance
0x0020	CAL_FAILED	Factory calibration solve failed
0x0040	HOLD_LAST	Firmware is holding the previous valid angle
0x0080	CAL_STORAGE_INVALID	NVM calibration CRC or block validation failed
0x0100	FACTORY_CAL_REQUIRED	Defaults are active and factory calibration is required

Configuration

Most tuning is compile-time and lives in source/app_encoder.h and source/app_adc.h.

Macro	Default	Purpose
ADC_SAMPLE_RATE_HZ	10000	Realtime ADC sample rate; keep CTIMER0 setup in sync
ENCODER_CAL_SAMPLE_COUNT	8192	Factory calibration sample count
ENCODER_TRACKING_BW_HZ	100.0f	Type-II PLL closed-loop bandwidth
ENCODER_TRACKING_ZETA	0.707f	Type-II PLL damping ratio
ENCODER_OUTPUT_DEADBAND_DEG	0.015f	Published angle dead-band threshold
ENCODER_ANGLE_COUNT_HYSTERESIS	1	Published count-domain hysteresis
ENCODER_MAG_WINDOW_BINS	32	Rotor-angle bins for magnitude display window
ENCODER_RUNTIME_TRIM_GAIN_STEP_LIMIT	0.02f	Per-update AGC gain trim limit
ENCODER_RUNTIME_TRIM_GAIN_TOTAL_LIMIT	0.5f	Total AGC gain trim limit

Known Notes and Limitations

• Multi-turn position is RAM-only. Power loss or reset clears the turn counter.
• Zero Here is also RAM-only. Factory calibration is the persistent zero source.
• Very slow motion below the output dead-band rate can be reported in steps by the published angle path.
• Runtime AGC is enabled only when NVM calibration is the active calibration source.
• The current Keil project metadata names an MCXA343 pack/device while the firmware sources target the MCXA344 series. Keep this in mind when changing device packs or regenerating the project.
• No top-level LICENSE, CONTRIBUTING, or SECURITY file is included in this repository snapshot.

Verification

This README describes the current firmware interfaces and constants. For a documentation-only change, verify with:

git diff --check

Firmware builds are still performed through Keil MDK:

C:\Keil_v5\UV4\uVision.com -b ind_encoder.uvprojx -t ind_encoder -j0

License

BSD-3-Clause, as declared by the source file SPDX headers.