steami_config: Add persistent configuration module.

[nedseb]

Context

The STeaMi board needs persistent configuration that survives power cycles. Initially, calibration values were stored in RAM and lost on reboot.

The config zone is a 1 KB area in the STM32F103 internal flash (gap between bootloader and interface firmware at 0x0800BC00). It survives interface firmware updates and clear_flash operations.

Flash layout

0x08000000 - 0x0800BBFF : Bootloader (47 KB, never touched)
0x0800BC00 - 0x0800BFFF : Config zone (1 KB)
0x0800C000 - 0x0801FBFF : Interface firmware (79 KB)
0x0801FC00 - 0x0801FFFF : DAPLink settings (1 KB)

Implemented usages

Usage	JSON key	Status
Board revision	rev	Done (#169)
Board name	name	Done (#169)
Temperature calibration	tc	Done (#168)
Magnetometer calibration	cal_mag	Done (#170)
Accelerometer calibration	cal_accel	Done (#171)
Boot counter	boot_count	Done (#172)

API overview

from steami_config import SteamiConfig
from daplink_flash import DaplinkFlash

config = SteamiConfig(DaplinkFlash(I2C(1)))
config.load()

# Board info
config.board_revision       # -> 3
config.board_name           # -> "STeaMi-01"

# Temperature calibration
config.set_temperature_calibration("hts221", gain=1.0, offset=-0.5)
config.get_temperature_calibration("hts221")  # -> {"gain": 1.0, "offset": -0.5}
config.apply_temperature_calibration(hts221_instance)

config.save()

Dependencies

• DAPLink firmware: steami: Add config zone in F103 internal flash gap DAPLink#4 (merged)

Sub-issues

• daplink_flash: Add config zone methods to driver. #167 — daplink_flash: config zone driver methods
• steami_config: Persist temperature calibration. #168 — Temperature calibration persistence
• steami_config: Add board revision and name storage. #169 — Board revision and name storage
• steami_config: Add magnetometer calibration storage. #170 — Magnetometer calibration storage
• steami_config: Add accelerometer calibration storage. #171 — Accelerometer calibration storage
• steami_config: Add boot counter. #172 — Boot counter
• Memory: investigate RAM usage when loading multiple drivers #175 — Memory investigation (closed: no longer reproducible with frozen drivers)

All sub-issues are now closed and the steami_config module is shipped with examples for each use case (show_config, populate_demo_config, calibrate_temperature, calibrate_magnetometer, calibrate_accelerometer, boot_counter).

[nedseb]

Implementation complete

The config zone is implemented using the STM32F103 internal flash (1 KB gap at 0x0800BC00 between bootloader and interface firmware), not the W25Q64 external flash.

Why internal flash?

Initial investigation showed that operations on the W25Q64 external flash via new I2C commands caused USB crashes. After extensive debugging, the root cause was identified as steami_i2c.c not being recompiled with the new commands (incremental build issue). However, the internal flash approach is superior:

• No SPI bus contention with DAPLink VFS
• Survives interface firmware updates (gap is never touched)
• Instant reads (memory-mapped)
• No timing issues with W25Q64 sector erase (400ms)

PRs

• Firmware: steami: Add config zone in F103 internal flash gap DAPLink#4
• Driver: daplink_flash: Add config zone support. #173

Hardware test results

10/10 tests passing: clear, write, read, offset writes, data preservation, clear_flash isolation, multi-page, large writes, stress cycles.