Portable C HAL interfaces

The portable C core depends on small capability-specific interfaces instead of one platform object. Platform adapters supply these capabilities while device code remains independent of Arduino, HERO, Linux, or any MCU vendor SDK.

rtd_acquire_spi_t

Introduced in: rtd-acquire 0.2.0

Declared in c/include/rtd_acquire/spi.h:

typedef struct {
    void *context;
    rtd_acquire_spi_settings_t settings;
    rtd_acquire_spi_transfer_fn transfer;
} rtd_acquire_spi_t;

The caller owns the opaque context and any storage it refers to. settings records the effective connection settings, and transfer performs one complete full-duplex transaction.

The transfer callback owns chip-select assertion and deassertion for the whole transaction. A platform adapter can implement that with hardware chip select or GPIO internally; portable device code does not need a separate chip-select API.

SPI transport success/failure is a platform-operation result. It is separate from normalized acquisition diagnostics reported by the measurement device.

rtd_acquire_spi_settings_t

typedef struct {
    uint8_t clock_polarity;
    uint8_t clock_phase;
    uint32_t clock_frequency_hz;
    rtd_acquire_spi_bit_order_t bit_order;
    uint8_t bits_per_word;
    bool chip_select_active_low;
} rtd_acquire_spi_settings_t;

These fields correspond to the observable Python SpiSettings semantics.

rtd_acquire_spi_result_t

typedef enum {
    RTD_ACQUIRE_SPI_OK = 0,
    RTD_ACQUIRE_SPI_IO_ERROR = 1
} rtd_acquire_spi_result_t;

rtd_acquire_delay_t

Introduced in: rtd-acquire 0.2.0

Declared in c/include/rtd_acquire/delay.h:

typedef struct {
    void *context;
    rtd_acquire_delay_us_fn delay_us;
} rtd_acquire_delay_t;

The caller owns the opaque context. The callback provides a blocking relative delay in whole microseconds:

typedef rtd_acquire_delay_result_t (*rtd_acquire_delay_us_fn)(
    void *context,
    uint32_t duration_us
);

A successful callback must not return before the requested interval has elapsed. Oversleep is allowed. This is intentionally a small blocking-delay capability, not a clock, scheduler, timer-allocation, or Arduino delay() abstraction.

Delay-operation success/failure remains separate from device-reported Measurement diagnostics.

rtd_acquire_delay_result_t

typedef enum {
    RTD_ACQUIRE_DELAY_OK = 0,
    RTD_ACQUIRE_DELAY_ERROR = 1
} rtd_acquire_delay_result_t;

Ownership and allocation

Neither HAL requires heap allocation. The interface structures can live in caller-owned static, automatic, or otherwise fixed storage, and their context pointers refer to storage whose lifetime is managed by the platform adapter or application.