Crate esp_config

esp-config

Documentation

Usage

esp-config takes a prefix (usually the crate name) and a set of configuration keys and default values to produce a configuration system that supports:

• Emitting rustc cfg’s for boolean keys
• Emitting environment variables for numbers
  • Along with decimal parsing, it supports Hex, Octal and Binary with the respective 0x, 0o and 0b prefixes.
• Emitting environment variables string values

Viewing the configuration

The possible configuration values are output as a markdown table in the crates OUT_DIR with the format {prefix}_config_table.md, this can then be included into the crates top level documentation. Here is an example of the output:

Name	Description	Default value
ESP_HAL_PLACE_SPI_DRIVER_IN_RAM	Places the SPI driver in RAM for better performance	false

Setting configuration options

For any available configuration option, the environment variable or cfg is always set based on the default value specified in the table. Users can override this by setting environment variables locally in their shell or the preferred option is to utilize cargo’s env section.

It’s important to note that due to a bug in cargo, any modifications to the environment, local or otherwise will only get picked up on a full clean build of the project.

To see the final selected configuration another table is output to the OUT_DIR with the format {prefix}_selected_config.md.

Capturing configuration values in the downstream crate

For all supported data types, there are helper macros that emit const code for parsing the configuration values.

• Numbers - esp_config_int!(integer_type, "ENV")
• Strings - esp_config_str!("ENV")
• Bool - esp_config_bool!("ENV")

In addition to environment variables, for boolean types rust cfg’s are emitted in snake case without the prefix.

Defining Configuration Options

Config options should be defined declaratively in a file called esp_config.yml.

Such a file looks like this:

crate: esp-bootloader-esp-idf

options:
- name: mmu_page_size
  description: ESP32-C2, ESP32-C6 and ESP32-H2 support configurable page sizes. This is currently only used to populate the app descriptor.
  default:
    - value: '"64k"'
  stability: !Stable stable-since-version
  constraints:
  - if: true
    type:
      validator: enumeration
      value:
      - 8k
      - 16k
      - 32k
      - 64k

- name: esp_idf_version
  description: ESP-IDF version used in the application descriptor. Currently it's not checked by the bootloader.
  default:
    - if: 'chip == "esp32c6"'
      value: '"esp32c6"'
    - if: 'chip == "esp32"'
      value: '"other"'
  active: true

- name: partition-table-offset
  description: "The address of partition table (by default 0x8000). Allows you to \
    move the partition table, it gives more space for the bootloader. Note that the \
    bootloader and app will both need to be compiled with the same \
    PARTITION_TABLE_OFFSET value."
  default:
    - if: true
      value: 32768
  stability: Unstable
  active: 'chip == "esp32c6"'

checks:
  - 'ESP_BOOTLOADER_ESP_IDF_CONFIG_PARTITION_TABLE_OFFSET >= 32768'

if and active are evalexpr expressions returning a boolean.

The expression supports these custom functions:

Function	Description
feature(String)	true if the given chip feature is present
cargo_feature(String)	true if the given Cargo feature is active
ignore_feature_gates()	Usually false but tooling will set this to true to hint that the expression is evaluated by e.g. a TUI

ignore_feature_gates() is useful to enable otherwise disabled functionality - e.g. to offer all possible options regardless of any active / non-active features.

The chip variable is populated with the name of the targeted chip (if the crate is using chip specific features).

The conditions for default and constraints are evaluated in order and the first match is taken no matter if there is more. This way you could have a catch-all condition as the last item by just specifying true.

checks is a list of checks which needs to pass for a valid configuration and is checked after all config values for the current config are applied. You can access the currently configured values to check them.

For more examples see the various esp_config.yml files in this repository.

Minimum Supported Rust Version (MSRV)

This crate is guaranteed to compile when using the latest stable Rust version at the time of the crate’s release. It might compile with older versions, but that may change in any new release, including patches.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Feature Flags

• build — Enable the generation and parsing of a config
• tui — The TUI

Macros

esp_config_bool

Parse the value of an environment variable as a bool at compile time.

esp_config_int

Parse the value of an environment variable as an integer at compile time.

esp_config_str

Get the string value of an environment variable at compile time.