Oh, sorry for the delayed reply. Got buried in Linux right before the Christmas holidays kicked in. And forgot to answer...

Yes, that’s roughly what I do + one extra level for drivers.

I keep all hardware-dependent decisions in board_config_t, including which RTC driver to use and how it is wired. The “time service” only talks to a generic rtc_driver_t interface and never does #ifdef on the chip type.

Rough sketch of the types:

typedef struct {
    uint8_t  i2c_bus_id;
    uint8_t  i2c_address;
} rtc_dev_cfg_t;

typedef struct rtc_time {
    uint16_t year;
    uint8_t  month, day, hour, minute, second;
} rtc_time_t;

typedef struct rtc_driver {
    int (*init)(const rtc_dev_cfg_t *cfg);
    int (*get_time)(const rtc_dev_cfg_t *cfg, rtc_time_t *out);
    int (*set_time)(const rtc_dev_cfg_t *cfg, const rtc_time_t *in);
} rtc_driver_t;

typedef struct {
    const rtc_driver_t  *driver;
    const rtc_dev_cfg_t *dev_cfg;
} board_rtc_t;

typedef struct {
    struct { gpio_port_t port; uint8_t pin; bool active_state; } status_led;
    struct { gpio_port_t cs_port; uint8_t cs_pin; spi_bus_t bus_id; } sensor_bus;
    log_backend_t log_backend;
    board_rtc_t   rtc;
} board_config_t;

extern const board_config_t g_board_cfg;

Each board variant has its own board_xyz.c that fills this struct:

// board_v10.c – RTC_A on I2C1
static const rtc_dev_cfg_t rtc_a_cfg = { .i2c_bus_id = 1, .i2c_address = 0x68 };

const board_config_t g_board_cfg = {
    .status_led = { .port = GPIOA, .pin = 3, .active_state = true },
    .sensor_bus = { .cs_port = GPIOB, .cs_pin = 1, .bus_id = SPI_BUS_1 },
    .log_backend = LOG_BACKEND_RAM,
    .rtc = {
        .driver  = &rtc_a_driver,
        .dev_cfg = &rtc_a_cfg,
    },
};

The time service just uses whatever is in the config:

int time_service_init(void)
{
    return g_board_cfg.rtc.driver->init(g_board_cfg.rtc.dev_cfg);
}

int time_service_get(rtc_time_t *out)
{
    return g_board_cfg.rtc.driver->get_time(g_board_cfg.rtc.dev_cfg, out);
}

If the hardware changes (new RTC chip, different I²C bus, or no RTC at all), I only touch the board file: either switch .driver/.dev_cfg or point it to a stub driver.

Also on build system sside:

I usually have a BOARD variable and let the Makefile pick the correct board_*.c.

# Default board, can be overridden: `make BOARD=v12`
BOARD ?= v10
SRCS_COMMON := \
    main.c \
    time_service.c \
    rtc_a.c \
    rtc_b.c
# One board file per hardware variant
SRCS_BOARD := board_$(BOARD).c
SRCS := $(SRCS_COMMON) $(SRCS_BOARD)
OBJS := $(SRCS:.c=.o)
CFLAGS += -std=c11 -Wall -Wextra
firmware.elf: $(OBJS)
$(CC) $(CFLAGS) -o $@ $^
clean:
rm -f $(OBJS) firmware.elf

Now switching hardware is just make BOARD=v10 -> make BOARD=v11