2026-05-12 BSP Interfaces

[simon-d-bmw]

2026-05-12 — IPB2 Arch Sync 2: BSP Interfaces in OpenBSW

Participants

• @simon-d-bmw
• @matthiaskessler
• @cristiancsordas
• Andrey Chekasin
• Andreu Montiel (Technica)
• Ramon Llorca (Technica)

Problem

Current OpenBSW convention: application code must include both UartConfig.h
and Uart.h. Proposal: make Uart.h include UartConfig.h directly so consumers
only need one include.

Key tensions

High performance vs. platform independence

• High-performance goal: compiler must see implementation details to optimize
  (e.g. inline, constant-fold register access). This means the interface
  must depend on the implementation — accepted design constraint.
• Platform independence goal: applications should be able to write code that
  compiles against any BSP target without including platform-specific headers.
  Challenge: does it make sense to write application code that is completely
  independent of the module configuration?

Static configuration benefit

• Static configuration (compile-time getInstance) avoids runtime lookup cost.
• This is the main argument for accepting the interface→implementation dependency.

Matthias's alternative: dependency injection

• Application receives a reference to the BSP module (e.g. Uart) from
  integration code, rather than constructing/getting it directly.
• Pros: cleaner dependency graph, easier testing.
• Not adopted in this meeting but not ruled out.

BSP module configuration structure

BSP module config consists of two parts:

1. Public (part of API): IDs — exposed in the module header
2. Private (local): register settings — platform-specific, not exposed

Configuration structures are used as forward declarations in headers to decouple
applications from hardware-specific properties. UartConfig is different on each
target.

Architecture observation (Andrey)

The current build dependency graph shows:

application → module_config → module

This is the reverse of the ideal direction. The group acknowledged this but
agreed it follows from the high-performance / static-config constraint.

Concepts (C++20) are used in CI builds but not enforced in production code.

Outcome

• Agreement reached on most points.
• No PR created yet.
• Next step: Cristian + Andrey create a PR; technical discussion continues there.

[rolandreichweinbmw]

Merged in main: 489448c