/* CLRC66303 SPI register access example, C99.
 * Adapt every board_hal_* function to the target MCU.
 * Configure SPI mode 0, MSB first, initially 100 kHz (bring-up choice).
 * This is a transport example, not a complete NFC protocol driver.
 */
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

/* Blocking transfer; return only after the last SCK edge.
 * Return false on timeout/error. Do not toggle NSS inside this function.
 */
extern bool board_hal_spi_transfer(const uint8_t *tx, uint8_t *rx,
                                   size_t length);
extern void board_hal_nss(bool high);
/* Meet the datasheet NSS-high interval: at least 50 ns.
 * Account for GPIO, timer and compiler behavior on the actual MCU.
 */
extern void board_hal_nss_high_gap(void);

#define CLRC663_VERSION_REG       UINT8_C(0x7F)
#define CLRC66303_EXPECTED_VERSION UINT8_C(0x1A)

/* Serialize access to this SPI bus for the whole transaction. */
static bool clrc663_frame(const uint8_t tx[2], uint8_t rx[2])
{
    board_hal_nss(false);
    const bool ok = board_hal_spi_transfer(tx, rx, 2u);
    board_hal_nss(true);       /* Release NSS even after a bus error. */
    board_hal_nss_high_gap();
    return ok;
}

bool clrc663_read_reg(uint8_t reg, uint8_t *value)
{
    if (reg > UINT8_C(0x7F) || value == NULL) {
        return false;
    }
    const uint8_t tx[2] = {
        (uint8_t)((reg << 1u) | 1u),  /* LSB = 1: read. */
        UINT8_C(0x00)                /* Dummy byte generates clocks. */
    };
    uint8_t rx[2] = {0u, 0u};
    if (!clrc663_frame(tx, rx)) {
        return false;
    }
    *value = rx[1];             /* Address-phase MISO is not the value. */
    return true;
}

bool clrc663_write_reg(uint8_t reg, uint8_t value)
{
    if (reg > UINT8_C(0x7F)) {
        return false;
    }
    const uint8_t tx[2] = {
        (uint8_t)(reg << 1u),   /* LSB = 0: write. */
        value
    };
    uint8_t rx[2] = {0u, 0u};
    return clrc663_frame(tx, rx);
}

/* Call after valid rails, settled IFSEL straps and PDOWN release.
 *  0 = expected CLRC66303 version; -1 = bus error; -2 = other version.
 * Log the observed byte; VersionReg is not an authenticity test.
 */
int clrc66303_check_version(uint8_t *observed)
{
    uint8_t version = 0u;
    if (!clrc663_read_reg(CLRC663_VERSION_REG, &version)) {
        return -1;
    }
    if (observed != NULL) {
        *observed = version;
    }
    return version == CLRC66303_EXPECTED_VERSION ? 0 : -2;
}