db492050e3
- Hall sensor + LP5562 EN wired-AND circuit design (DRV5032FB/FE, 1M pull-up, open-drain topology) with three interaction modes: boot-time recovery, tap-to-swap, hold-to-confirm recovery - NTAG5 config check tool (tools/ntag5_config_check.py) using uFCoder library for ISO15693 transparent mode via uFR Zero reader. Supports inventory + addressed mode for multi-tag fields. - Updated DEVELOPMENT_PLAN with I2C bus management notes for LP5562 (0x30) + NTAG5Link (0x54) shared bus - Updated README with wired-AND hardware diagram, hall sensor interaction section, and updated wiring table - Updated CLAUDE.md with LP5562 EN wired-AND topology docs - Updated STATUS.md with hall sensor decisions and hardware inventory Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
117 lines
5.3 KiB
Markdown
117 lines
5.3 KiB
Markdown
# xblink Development Guide
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Embedded Rust firmware for a battery-free, NFC-powered LED implant. The NTAG5Link harvests energy from an NFC field and provides EEPROM storage for LED patterns. A SAMD21E MCU reads patterns from EEPROM, programs LP5562 execution engines, then sleeps while the LP5562 autonomously drives RGBW LEDs.
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## Build Commands
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```bash
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# Build release firmware
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cargo build --release
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# Flash via UF2 bootloader (XIAO M0: double-tap RST to enter bootloader)
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cargo hf2 --release
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# Auto-flash: watches for bootloader USB device, flashes when detected
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./flash_when_ready.sh
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```
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## Target
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- Architecture: `thumbv6m-none-eabi` (ARM Cortex-M0+)
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- Dev board: Seeed XIAO M0 (SAMD21G18A) — will port to bare SAMD21E18A later
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- LED driver: LP5562EVM (TI evaluation module, RGBW, I2C addr 0x30)
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- NFC: NTAG5Link Click board (MikroElektronika)
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## Dependencies
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| Crate | Version | Purpose |
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|-------|---------|---------|
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| `xiao_m0` | 0.13 | Board support package (dev board phase) |
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| `panic-halt` | 0.2 | Minimal panic handler for `no_std` |
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| `cortex-m` | 0.7 | Cortex-M runtime, `critical-section-single-core` feature |
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| `embedded-hal` | 1.0.0 | Hardware abstraction traits (I2C, GPIO, delay) |
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When porting to bare SAMD21E: replace `xiao_m0` with `atsamd-hal = { version = "0.17", features = ["samd21e"] }` and add `cortex-m-rt = "0.7"`.
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## Project Structure
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```
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src/
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main.rs # Entry point: boot, pattern load, sleep/wake loop
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led/
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mod.rs # LP5562 re-exports (LedController trait added later, M10)
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lp5562.rs # LP5562 driver (from ../ntag5-samd21-lp562/)
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ntag5/ # NTAG5Link I2C slave driver (M4+)
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pattern/ # Pattern format and engine builder (M5+)
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```
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## Architecture Conventions
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- **`no_std` only**: No heap allocation. Fixed-size arrays and stack-only data structures.
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- **`embedded-hal` generics**: All hardware drivers must be generic over `embedded_hal::i2c::I2c` (1.0 traits). Never use concrete HAL types in driver code.
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- **Hardware-first**: Get hardware working before extracting abstractions. Traits and formats are designed after hands-on experience, not before.
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- **Error types**: Use `Error<E>` enum wrapping underlying I2C error with `From<E>` impl (see LP5562 driver pattern).
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- **Register addresses**: Place in a `reg` submodule as `pub const` values.
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- **`const fn`**: Prefer `const fn` where possible (see `EngineCommand` builder in LP5562 driver).
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- **No `unsafe`**: Avoid unless absolutely necessary for hardware access.
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## LP5562 Timing Constraints
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The LP5562 driver does NOT enforce timing delays internally — the caller is responsible:
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- **>= 500 us** after `enable()` before any other commands
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- **>= 488 us** between consecutive ENABLE register writes (engine exec changes)
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- **>= 153 us** between consecutive OP_MODE register writes (engine mode changes)
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- When transitioning from Run, set exec to Hold first, then change mode
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## Key I2C Addresses
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Both devices share the same I2C bus (A4/A5). Non-conflicting addresses — no bus arbitration issues.
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| Device | Address | Notes |
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|--------|---------|-------|
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| LP5562 | 0x30 | ADDR_SEL pins both low (LP5562EVM default) |
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| NTAG5Link | 0x54 | Default NTP53x2 I2C slave address |
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## NTAG5Link I2C Register Map (MCU-side)
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The MCU accesses NTAG5Link as a standard I2C slave — plain register read/write, NOT the NFC-side ISO15693 custom commands used by the Python ntag5sensor tooling.
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| Region | Address Range | Size | Notes |
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|--------|--------------|------|-------|
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| Session registers | 0x00-0x06 | 7 bytes | Volatile, runtime config |
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| Configuration | 0x37-0x3F | Varies | Persistent, EEPROM-backed |
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| EH config | 0x3D | 1 byte | Energy harvesting voltage/current |
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| SRAM | 0xF8-0xFF | 256 bytes | 64 x 4-byte blocks, volatile |
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| EEPROM user memory | blocks 0x00-0x1FF | 2048 bytes | 512 x 4-byte blocks |
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Key config constants (from `../ntag5sensor/vicinity/ntag5link.py`):
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- `CONFIG_1_USE_CASE_CONF_I2C_SLAVE = 0 << 4` — NTAG5 as I2C slave (our mode)
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- `CONFIG_1_ARBITER_MODE_SRAM_PASSTHROUGH = 2 << 2` — SRAM pass-through for NFC↔I2C
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- `CONFIG_1_SRAM_ENABLE = 1 << 1` — Enable SRAM access
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- `CONFIG_0_EH_MODE_LOW_FIELD_STRENGTH = 2 << 2` — EH mode for phone NFC
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## Hardware Wiring (Dev Board)
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| XIAO Pin | Connection | Function |
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|----------|------------|----------|
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| A4 (SDA) | LP5562 SDA, NTAG5 SDA | Shared I2C data |
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| A5 (SCL) | LP5562 SCL, NTAG5 SCL | Shared I2C clock |
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| D0/A0 | LP5562 EN line (open-drain) | Wired-AND with hall sensor, pull-up to VCC |
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| TBD (EIC) | Hall sensor output | EIC wake + wired-AND to LP5562 EN line |
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| TBD (EIC) | NTAG5 FD pin | Field detect / SRAM write indication (EIC wake) |
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**LP5562 EN wired-AND**: D0/A0 (open-drain) and hall sensor (open-drain, active-low) both connect to LP5562 EN with a 1M pull-up. Either can force EN low. Magnet kills LEDs at hardware level regardless of MCU state.
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## Testing
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- **Hardware**: XIAO M0 + LP5562EVM + NTAG5Link Click (when jumpers available)
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- **PCSC reader**: Use `../ntag5sensor/` Python tooling with ACR1552 reader
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- **Phone NFC**: VivoKey RawNFC app for SRAM mailbox testing
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- **Phone app**: DT NFC Identifier for basic tag info
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## Sibling Projects
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- `../ntag5-samd21-lp562/` — Original LP5562 driver + smoke test (xblink's `src/led/lp5562.rs` is synced from here)
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- `../ntag5sensor/` — NTAG5Link command reference (`vicinity/ntag5link.py`), I2C patterns (`vicinity/i2cbase.py`)
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