# eFuse Interface ## Contents * [Introduction](#intro) * [eFuse Read Functions](#read-funcs) * [eFuse Layout](#layout) * [Example](#example)

## Introduction The eFuse interface provides read access to the ESP32-S3 one-time programmable (OTP) fuse memory. eFuses store factory-provisioned board identity data such as the LoRa-WAN DevEUI, WiFi MAC address, serial number, and hardware identifiers. The values stored in eFuses are written once during manufacturing and cannot be changed afterwards. This module allows micropython scripts to retrieve these values at runtime. An optional internal RAM cache can be enabled (`SDK_BOARD_EFUSE_INTERNAL_CACHE_ENABLE`) so that the eFuse block is read from hardware only once at startup, with subsequent reads served from memory.

## eFuse Read Functions All read functions take no arguments and return a `bytes` object containing the raw value read from the eFuse block. The module is imported as `efuse_if`. * `efuse_if.layout_version()` returns the eFuse user-data block layout version (1 byte). * `efuse_if.lora_mac()` returns the LoRa-WAN DevEUI (8 bytes). * `efuse_if.serial_number()` returns the board serial number (6 bytes). * `efuse_if.hw_id()` returns the manufacturer hardware ID (3 bytes). * `efuse_if.project_id()` returns the project-specific ID (3 bytes). * `efuse_if.wifi_mac()` returns the WiFi MAC address (6 bytes). ### Optional LoRa Key Functions The following functions are only available when LoRa key storage on eFuses is enabled (`SDK_BOARD_LORA_WAN_KEYS_ON_EFUSES`): * `efuse_if.lora_app_key()` returns the LoRa-WAN OTAA AppKey (16 bytes). * `efuse_if.lora_nwk_key()` returns the LoRa-WAN OTAA NwkKey (16 bytes). ### Test Function (Virtual eFuse Mode Only) When building with `CONFIG_EFUSE_VIRTUAL` enabled for development or testing: * `efuse_if.write_test_lora_keys(AppKey=, NwkKey=)` writes test LoRa keys to the virtual eFuse block. Both keyword arguments must be provided as 16-byte buffers.

## eFuse Layout The board identity data is stored in **EFUSE_BLK3** (User Data) on the ESP32-S3. The current layout (version 0) is: | Field | Size | Description | |-----------------|----------|--------------------------| | LPWAN_MAC | 8 bytes | LoRa-WAN DevEUI | | SERIAL_NUMBER | 6 bytes | Board serial number | | HW_ID | 3 bytes | Hardware ID | | PROJECT_ID | 3 bytes | Project-specific ID | | Reserved | 4 bytes | Reserved for future use | | LAYOUT_VERSION | 1 byte | Layout version number | | WIFI_MAC | 6 bytes | WiFi MAC address | | CRC8 | 1 byte | CRC8 checksum | When LoRa key storage is enabled, the AppKey and NwkKey (16 bytes each) are stored in a separate eFuse KEY block (configurable, default KEY5).

## Example ```python import efuse_if # read the LoRa-WAN DevEUI deveui = efuse_if.lora_mac() print("DevEUI:", deveui.hex()) # read the WiFi MAC address wifi = efuse_if.wifi_mac() print("WiFi MAC:", wifi.hex()) # read the board serial number sn = efuse_if.serial_number() print("Serial:", sn.hex()) # read hardware and project identifiers hw = efuse_if.hw_id() proj = efuse_if.project_id() print("HW ID:", hw.hex()) print("Project ID:", proj.hex()) # read the layout version ver = efuse_if.layout_version() print("Layout version:", int.from_bytes(ver, 'little')) ``` Example output: ``` DevEUI: 70b3d54992a6920f WiFi MAC: 7c5189020340 Serial: 000000000000 HW ID: 010000 Project ID: 000000 Layout version: 0 ```