# Hardware Abstraction and Portability

> **The criterion.** Minimizing vendor lock-in over a long project lifecycle: pre-ported Board Support
> Packages for your architecture, and a unified HAL for common peripherals (GPIO, UART, SPI, I2C, CAN) so
> switching chips doesn't force an application rewrite.

## How Revera answers it

**Portability is a core strength; peripheral breadth is deliberately minimal in 0.1.0.** The kernel is
portable across **10 CPU-architecture ports** (ARM Cortex-M / -A / -R, RISC-V, AURIX TriCore, plus HAL-level
C2000 / MSP430) and **14 boards**, behind a clean board contract: a board is one `make/board/<name>.mk`
fragment plus a small BSP, and adding a board or an arch is a drop-in `.mk` — nothing in the kernel changes.
The 0.1.0 HAL is intentionally small: console, GPIO, UART (TX), and clock/timer. A rich peripheral HAL exists
in the project's history and is port-forward-ready (below).

## Feature · how to turn it on · how to use it · where it works

| Feature (in 0.1.0) | Use these APIs | Where |
|---|---|---|
| GPIO / digital I/O | `tk_dio_read` / `write` / `flip`, `tk_port_config_pin` (`tk_dir_t`, `tk_pull_t`) | all boards |
| GPIO edge → IRQ | `tk_dio_irq_init` / `enable_channel` / `enable_pin` (edge → callback) | boards with it |
| UART (transmit) + console | `tk_uart_init` / `write` / `setup`; `tk_console_init`, `tk_print`, `tk_print_u32` | all boards |
| Clock / timekeeping | `tk_mcu_init`, `tk_mcu_clock_hz`; `tk_time_init` / `tk_time_ms` / `tk_time_us` | all boards |
| Board bring-up | `tk_board_init` | all boards |

*Full signatures and contracts: [API reference — HAL](../reference/api.md).*

## Available from the project's history (roadmap / on request — not in 0.1.0)

A full peripheral HAL and off-chip device layer were implemented (many HW-proven) before the reshape and can
be ported forward. This is the port-ready inventory, honestly *not* shipping in 0.1.0:

- **On-chip peripherals:** ADC (one-shot) · I²C (master + event-driven slave) · SPI (master) · PWM (per-mille
  duty) · GPT (application countdown timers) · ICU (input capture) · RTC (low-power counter) · UART **receive**
  ring · GPIOTE zero-CPU hardware routing (PPI) · on-die TEMP · RNG · CRC-16 · watchdog MCAL (mode-based).
- **Off-chip device drivers** (board-independent): HD44780 LCD · MCP2515 CAN controller · PCF8574 I²C GPIO
  expander · PN532 NFC.

Each carried a portable MCAL-style contract (`tk_<periph>_*`) with per-board backends; see
[HAL architecture](../architecture/hal-architecture.md) §14 for the distillation rationale and the deferred
list, and [the roadmap](../roadmap.md).

## Limits

- 0.1.0's HAL covers GPIO / UART-TX / timer / console only; **UART receive** and everything above is roadmap.
- Portability (the arch/board contract) is the strength here, not peripheral coverage.

## Learn more

- **How it works:** [HAL architecture](../architecture/hal-architecture.md) · [board contract](../architecture/board-contract.md) ·
  [arch interface](../architecture/arch-interface.md) · [board bring-up guide](../guides/board-bringup.md).
- **Full API:** [API reference](../reference/api.md).