Adding a board

This guide describes the project’s BSP conventions and the steps required to bring up another board. The BSP path is src/bsp/<manufacturer>/<platform>/<codename>/:

src/bsp/ampere/xiao_esp32c3/terra/
├── board_terra.h
├── board_terra.cpp
└── device_info.cpp

The manufacturer identifies the board vendor, platform identifies its shared compute module or platform family, and codename identifies the product. This is the EWP directory convention, not a universal C++ standard.

Board contract and selection

Implement ersa::board::Board and a board-specific Pins subclass. The selected BSP provides ersa::board::boardImplementation() and returns its static board instance as a Board&. Board::current() is available before peripheral initialization, so startup and services never need to include a concrete board class. The selected BSP provider is guarded by its Kconfig board symbol; exactly one provider must be enabled.

The board implementation owns composition: pin maps, board capabilities, and instances of the platform and peripheral drivers used by the product. It returns generic interfaces (IDisplay, IRtc, IBattery, IInput, IBluetooth, ICompanionSource, IWifiRadio, and IPowerManagement). Keep concrete driver names out of application and service APIs.

Pins and pin control

include/ersa/board/pins.h groups pin records by I2C, SPI, display, buttons, and battery. Each pin carries its number, function, direction, pull, and active level. Put physical assignments in the BSP’s Pins subclass, then let the platform pin controller apply electrical settings and configure buses.

This typed C++ pin contract is the project’s pinctrl description. Device Tree is useful when the selected RTOS/build system consumes DTS bindings; this Arduino/ESP-IDF configuration does not, so an unconsumed DTS file would not configure hardware. ESP-IDF Kconfig selects the board and required driver options.

HAL and driver placement

• Add a platform-neutral contract under include/ersa/hal/ when code needs a hardware capability. Examples are IDisplay, IBluetooth, IWifiRadio, and IPowerManagement.
• Put MCU, RTOS, GPIO controller, clock, and vendor SDK adapters under src/hal/<platform>/.
• Put chip or peripheral implementations under src/drivers/<domain>/.
• Compose and inject those objects from the selected BSP.

The display contract must not expose SSD1681 or Adafruit GFX types. The same principle applies to Bluetooth stacks, bus libraries, storage backends, and power APIs. Create an audio contract when the product has real audio hardware and an implementation to bind; do not add an unused placeholder interface.

Bring-up checklist

1. Add board_<codename>.h/.cpp, device_info.cpp, and a Pins subclass in the manufacturer/platform/codename directory.
2. Add the board Kconfig symbol in src/Kconfig; guard the BSP’s boardImplementation() definition with that symbol and keep exactly one provider selected.
3. Implement every required Board method and return generic HAL interfaces. Initialize board pin control before polling buttons or starting peripheral services.
4. Add or reuse platform and peripheral drivers under their respective directories. Keep pin numbers and board identity out of generic HAL contracts.
5. Add mock coverage for new contracts and update the feature, architecture, and board documentation.
6. Run make test, make firmware, and make docs. Verify button polarity, display refresh, radios, sleep/wake sources, and current draw on hardware.

For architecture boundaries, see HAL and board architecture.