//
// Created by dell on 24-12-20.
//

#include "i2c.h"

/*!
    \brief      configure the GPIO ports
    \param[in]  none
    \param[out] none
    \retval     none
*/
void i2c_gpio_config(void) {
    /* enable IIC GPIO clock */
    rcu_periph_clock_enable(RCU_GPIO_I2C);

    /* connect I2C_SCL_PIN to I2C_SCL */
    gpio_af_set(I2C_SCL_PORT, I2C_GPIO_AF, I2C_SCL_PIN);
    /* connect I2C_SDA_PIN to I2C_SDA */
    gpio_af_set(I2C_SDA_PORT, I2C_GPIO_AF, I2C_SDA_PIN);
    /* configure GPIO pins of I2C */
    gpio_mode_set(I2C_SCL_PORT, GPIO_MODE_AF, GPIO_PUPD_PULLUP, I2C_SCL_PIN);
    gpio_output_options_set(I2C_SCL_PORT, GPIO_OTYPE_OD, GPIO_OSPEED_50MHZ, I2C_SCL_PIN);
    gpio_mode_set(I2C_SDA_PORT, GPIO_MODE_AF, GPIO_PUPD_PULLUP, I2C_SDA_PIN);
    gpio_output_options_set(I2C_SDA_PORT, GPIO_OTYPE_OD, GPIO_OSPEED_50MHZ, I2C_SDA_PIN);
}

/*!
    \brief      configure the I2CX interface
    \param[in]  none
    \param[out] none
    \retval     none
*/
i2c_result_t i2c_config(void) {
    /* configure I2C GPIO */
    i2c_gpio_config();
    /* enable I2C clock */
    rcu_periph_clock_enable(RCU_I2C);
    /* configure I2C clock */
    i2c_clock_config(I2C0, I2C_SPEED, I2C_DTCY_2);
    /* configure I2C address */
    i2c_mode_addr_config(I2C0, I2C_I2CMODE_ENABLE, I2C_ADDFORMAT_7BITS, 0xA0);
    /* enable I2CX */
    i2c_enable(I2C0);
    /* enable acknowledge */
    i2c_ack_config(I2C0, I2C_ACK_ENABLE);

    return I2C_RESULT_SUCCESS;
}

/* wait for SCL to go high, return true if successful, false if timeout */
static bool i2c_wait_scl_high(uint16_t max_wait_time) {
    while (max_wait_time--) {
        if (gpio_input_bit_get(I2C_SCL_PORT, I2C_SCL_PIN)) {
            return true;
        }
        delay_10us(1);
    }
    return false;
}

/* generate one manual SCL pulse; return true if SCL observed high (no stuck/overstretch) */
static bool i2c_generate_scl_pulse(void) {
    GPIO_BC(I2C_SCL_PORT) = I2C_SCL_PIN;   /* drive SCL low */
    delay_10us(1);
    GPIO_BOP(I2C_SCL_PORT) = I2C_SCL_PIN;  /* release SCL (open-drain -> high via pull-up) */
    return i2c_wait_scl_high(200);         /* wait up to ~2ms for clock stretching release */
}

/*!
    \brief      reset I2C bus
    \param[in]  none
    \param[out] none
    \retval     none
*/
i2c_result_t i2c_bus_reset(void) {
    /* 1. Disable & deinit peripheral so pins can be fully controlled */
    i2c_disable(I2C0);
    i2c_deinit(I2C0);

#ifdef DEBUG_VERBOSE
    printf("I2C bus reset\r\n");
#endif

    /* 2. Configure SCL/SDA as GPIO open-drain outputs with pull-up and release them */
    gpio_mode_set(I2C_SCL_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_PULLUP, I2C_SCL_PIN);
    gpio_mode_set(I2C_SDA_PORT, GPIO_MODE_OUTPUT, GPIO_PUPD_PULLUP, I2C_SDA_PIN);
    gpio_output_options_set(I2C_SCL_PORT, GPIO_OTYPE_OD, GPIO_OSPEED_50MHZ, I2C_SCL_PIN);
    gpio_output_options_set(I2C_SDA_PORT, GPIO_OTYPE_OD, GPIO_OSPEED_50MHZ, I2C_SDA_PIN);
    gpio_bit_set(I2C_SCL_PORT, I2C_SCL_PIN); /* release SCL */
    gpio_bit_set(I2C_SDA_PORT, I2C_SDA_PIN); /* release SDA */

#ifdef DEBUG_VERBOSE
    printf("I2C bus reset: SCL = %d, SDA = %d\r\n", gpio_input_bit_get(I2C_SCL_PORT, I2C_SCL_PIN), gpio_input_bit_get(I2C_SDA_PORT, I2C_SDA_PIN));
#endif

    /* 3. Double sample to confirm bus state */
    delay_10us(1);
    bool scl_value1 = gpio_input_bit_get(I2C_SCL_PORT, I2C_SCL_PIN);
    bool sda_value1 = gpio_input_bit_get(I2C_SDA_PORT, I2C_SDA_PIN);
    delay_10us(1);
    bool scl_value2 = gpio_input_bit_get(I2C_SCL_PORT, I2C_SCL_PIN);
    bool sda_value2 = gpio_input_bit_get(I2C_SDA_PORT, I2C_SDA_PIN);

    /* 4. If SCL low -> stuck (cannot proceed) */
    if (!scl_value2) {
#ifdef DEBUG_VERBOSE
        printf("I2C bus reset: SCL stuck low\r\n");
#endif
        return I2C_RECOVERY_SCL_STUCK_LOW;
    }

    /* 5. Fast path: bus idle */
    if (scl_value1 && sda_value1 && scl_value2 && sda_value2) {
        i2c_config();
#ifdef DEBUG_VERBOSE
        printf("I2C bus reset: bus idle\r\n");
#endif
        return I2C_RECOVERY_OK;
    }

    /* 6. SDA low: attempt to free by generating up to I2C_RECOVERY_CLOCKS pulses */
    if (scl_value2 && !sda_value2) {
        bool sda_released = false;
#ifdef DEBUG_VERBOSE
        printf("I2C bus reset: SCL will try to free SDA\r\n");
#endif
        for (uint8_t i = 0; i < I2C_RECOVERY_CLOCKS && !sda_released; i++) {
            if (!i2c_generate_scl_pulse()) {
                return I2C_RECOVERY_SCL_STUCK_LOW; /* SCL failed to go high */
            }
            if (gpio_input_bit_get(I2C_SDA_PORT, I2C_SDA_PIN)) {
                sda_released = true;
            }
        }
        if (!sda_released) {
            return I2C_RECOVERY_SDA_STUCK_LOW;
        }
        /* 7. Generate a STOP condition to leave bus in idle state */
#ifdef DEBUG_VERBOSE
        printf("I2C bus reset: generating STOP condition\r\n");
#endif
        gpio_bit_reset(I2C_SDA_PORT, I2C_SDA_PIN); /* SDA low */
        delay_10us(1);
        gpio_bit_set(I2C_SCL_PORT, I2C_SCL_PIN);   /* ensure SCL high */
        delay_10us(1);
        gpio_bit_set(I2C_SDA_PORT, I2C_SDA_PIN);   /* SDA rising while SCL high -> STOP */
        delay_10us(1);
    }

#ifdef DEBUG_VERBOSE
        printf("I2C bus reset: bus recovered\r\n");
#endif
    /* 8. Reconfigure & enable peripheral */
    i2c_config();
    return I2C_RECOVERY_OK;
}

/**
 * @brief 扫描I2C总线，查找连接的设备
 *
 * 该函数会扫描I2C总线上的所有地址（1到126），并尝试与每个地址进行通信。
 * 如果在某个地址上发现了设备，则会打印出该设备的地址。
 * 最后会打印出找到的设备总数。
 */
void i2c_scan(void) {
    uint32_t timeout;
    uint8_t address;
    int found_devices = 0;

    // printf("Scanning I2C bus...\r\n");
    const char* msg1 = "Scanning I2C bus...\r\n";
    for (uint8_t i = 0; msg1[i] != '\0'; i++) {
        while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
        usart_data_transmit(I2C_DEBUG_UART, msg1[i]);
    }
    while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TC) == RESET) {}

    for (address = 1; address < 127; address++) {
        timeout = 0;

        // 生成起始条件
        while (i2c_flag_get(I2C0, I2C_FLAG_I2CBSY) && (timeout < I2C_TIME_OUT))
            timeout++;
        if (timeout >= I2C_TIME_OUT) {
            continue; // 超时，跳过该地址
        }
        i2c_start_on_bus(I2C0);
        timeout = 0;

        // 等待起始条件发送完成
        while (!i2c_flag_get(I2C0, I2C_FLAG_SBSEND) && (timeout < I2C_TIME_OUT))
            timeout++;
        if (timeout >= I2C_TIME_OUT) {
            continue; // 超时，跳过该地址
        }
        i2c_master_addressing(I2C0, (address << 1), I2C_TRANSMITTER);
        timeout = 0;

        // 等待地址发送完成
        while (!i2c_flag_get(I2C0, I2C_FLAG_ADDSEND) && (timeout < I2C_TIME_OUT))
            timeout++;
        if (timeout < I2C_TIME_OUT) {
            i2c_flag_clear(I2C0, I2C_FLAG_ADDSEND);
            // printf("Found device at 0x%02X\r\n", address);
            const char* msg2_prefix = "Found device at 0x";
            for (uint8_t i = 0; msg2_prefix[i] != '\0'; i++) {
                while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
                usart_data_transmit(I2C_DEBUG_UART, msg2_prefix[i]);
            }
            // 发送地址的十六进制表示
            uint8_t hex_chars[] = "0123456789ABCDEF";
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
            usart_data_transmit(I2C_DEBUG_UART, hex_chars[(address >> 4) & 0x0F]);
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
            usart_data_transmit(I2C_DEBUG_UART, hex_chars[address & 0x0F]);
            const char* msg2_suffix = "\r\n";
            for (uint8_t i = 0; msg2_suffix[i] != '\0'; i++) {
                while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
                usart_data_transmit(I2C_DEBUG_UART, msg2_suffix[i]);
            }
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TC) == RESET) {}
            found_devices++;
        }

        // 生成停止条件
        i2c_stop_on_bus(I2C0);

        timeout = 0;

        while (i2c_flag_get(I2C0, I2C_FLAG_STPDET) && (timeout < I2C_TIME_OUT))
            timeout++;
    }

    if (found_devices == 0) {
        // printf("No I2C devices found.\r\n");
        const char* msg3 = "No I2C devices found.\r\n";
        for (uint8_t i = 0; msg3[i] != '\0'; i++) {
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
            usart_data_transmit(I2C_DEBUG_UART, msg3[i]);
        }
        while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TC) == RESET) {}
    } else {
        // printf("Total %d I2C devices found.\r\n", found_devices);
        const char* msg4_prefix = "Total ";
        for (uint8_t i = 0; msg4_prefix[i] != '\0'; i++) {
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
            usart_data_transmit(I2C_DEBUG_UART, msg4_prefix[i]);
        }
        // 发送设备数量
        if (found_devices >= 10) {
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
            usart_data_transmit(I2C_DEBUG_UART, '0' + (found_devices / 10));
        }
        while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
        usart_data_transmit(I2C_DEBUG_UART, '0' + (found_devices % 10));
        const char* msg4_suffix = " I2C devices found.\r\n";
        for (uint8_t i = 0; msg4_suffix[i] != '\0'; i++) {
            while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TBE) == RESET) {}
            usart_data_transmit(I2C_DEBUG_UART, msg4_suffix[i]);
        }
        while (usart_flag_get(I2C_DEBUG_UART, USART_FLAG_TC) == RESET) {}
    }
}

i2c_result_t i2c_write_16bits(uint8_t slave_addr, uint8_t reg_addr, uint8_t data[2]) {
    i2c_state_t state = I2C_STATE_START;
    uint16_t timeout = 0;
    uint8_t retry_count = 0;

    /* parameter validation */
    if (data == NULL || slave_addr > 0x7F) {
        return I2C_RESULT_INVALID_PARAM;
    }

    while (retry_count < I2C_MAX_RETRY) {
        switch (state) {
            case I2C_STATE_START:
                timeout = 0;

                /* wait for bus to be idle */
                while (i2c_flag_get(I2C0, I2C_FLAG_I2CBSY) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                i2c_start_on_bus(I2C0);
                timeout = 0;
                state = I2C_STATE_SEND_ADDRESS;
                break;

            case I2C_STATE_SEND_ADDRESS:
                /* wait for start condition to be sent. SBSEND flag */
                while((!i2c_flag_get(I2C0, I2C_FLAG_SBSEND)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* send slave address */
                i2c_master_addressing(I2C0, slave_addr << 1, I2C_TRANSMITTER);
                timeout = 0;
                state = I2C_STATE_CLEAR_ADDRESS;
                break;

            case I2C_STATE_CLEAR_ADDRESS:
                /* wait for address to be acknowledged.ADDSEND set means i2c slave sends ACK */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_ADDSEND)) && (!i2c_flag_get(I2C0, I2C_FLAG_AERR)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                } else if (i2c_flag_get(I2C0, I2C_FLAG_ADDSEND))
                {
                    i2c_flag_clear(I2C0, I2C_FLAG_ADDSEND);
                    timeout =0;
                    state = I2C_STATE_TRANSMIT_REG;
                    break;
                } else {
                    i2c_flag_clear(I2C0, I2C_FLAG_AERR);
                    timeout =0;
#ifdef DEBUG_VERBOES
                    printf("IIC write failed for Error Slave Address. \n");
#endif
                    return I2C_RESULT_NACK;
                }

            case I2C_STATE_TRANSMIT_REG:
                /* wait until the transmit data buffer is empty */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_TBE)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* send register address */
                i2c_data_transmit(I2C0, reg_addr);
                timeout = 0;
                state = I2C_STATE_TRANSMIT_DATA;
                break;

            case I2C_STATE_TRANSMIT_DATA:
                /* wait until the transmit data buffer is empty */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_TBE)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* send register MSB value */
                i2c_data_transmit(I2C0, data[0]);
                timeout = 0;
                
                /* wait until the transmit data buffer is empty */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_TBE)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                if (i2c_flag_get(I2C0, I2C_FLAG_AERR)) {
                    i2c_stop_on_bus(I2C0);
                    return I2C_RESULT_NACK;
                } else if (i2c_flag_get(I2C0, I2C_FLAG_BERR) || i2c_flag_get(I2C0, I2C_FLAG_LOSTARB)) {
                    // 可按需清标志
                    i2c_stop_on_bus(I2C0);
                    return I2C_RESULT_ERROR;
                }

                /* send register LSB value */
                i2c_data_transmit(I2C0, data[1]);
                timeout = 0;
                
                /* wait until BTC bit is set */
                while (!i2c_flag_get(I2C0, I2C_FLAG_BTC) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                state = I2C_STATE_STOP;
                break;

            case I2C_STATE_STOP:
                /* send a stop condition to I2C bus */
                i2c_stop_on_bus(I2C0);

                timeout = 0;
                while ((I2C_CTL0(I2C0) & I2C_CTL0_STOP) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* i2c master sends STOP signal successfully */
                /* success */
                return I2C_RESULT_SUCCESS;

            case I2C_STATE_ERROR:
                /* send a stop condition to I2C bus */
                i2c_stop_on_bus(I2C0);

                timeout = 0;
                while ((I2C_CTL0(I2C0) & I2C_CTL0_STOP) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    return I2C_RESULT_ERROR;
                }

                i2c_flag_clear(I2C0, I2C_FLAG_AERR);
                i2c_flag_clear(I2C0, I2C_FLAG_BERR);
                i2c_flag_clear(I2C0, I2C_FLAG_LOSTARB);

                retry_count ++;
                if (retry_count >= I2C_MAX_RETRY)
                {
#ifdef DEBUG_VERBOES
                    printf("IIC write failed after %d retries\n", I2C_MAX_RETRY);
#endif
                    return I2C_RESULT_ERROR;
                }

                /* reset state machine for retry */
                state = I2C_STATE_START;
                timeout = 0;

                /* small delay before retry */
                delay_10us(10);
                break;
                
            default:
                state = I2C_STATE_START;
                break;
        }
    }
    return I2C_RESULT_TIMEOUT;
}

i2c_result_t i2c_read_16bits(uint8_t slave_addr, uint8_t reg_addr, uint8_t *data) {
    i2c_state_t state = I2C_STATE_START;
    uint16_t timeout = 0;
    uint8_t retry_count = 0;
    bool write_phase = true;

    // 参数检查：防止空指针和非法地址
    if (data == NULL || slave_addr > 0x7F) {
        return I2C_RESULT_INVALID_PARAM;
    }

    /* enable acknowledge */
    i2c_ack_config(I2C0, I2C_ACK_ENABLE);

    while (retry_count < (uint8_t)I2C_MAX_RETRY) {
        switch (state) {
            case I2C_STATE_START:
                timeout = 0;

                // wait for bus to be idle
                while (i2c_flag_get(I2C0, I2C_FLAG_I2CBSY) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                // send start condition
                i2c_start_on_bus(I2C0);
                state = I2C_STATE_SEND_ADDRESS;
                timeout = 0;
                break;

            case I2C_STATE_SEND_ADDRESS:
                /* wait for start condition to be sent  */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_SBSEND)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                // send slave address
                if (write_phase) {
                    /* write phase: send address with write bit */
                    i2c_master_addressing(I2C0, (slave_addr << 1), I2C_TRANSMITTER);
                } else {
                    /* read phase: send address with read bit */
                    i2c_master_addressing(I2C0, (slave_addr << 1) | 0x01, I2C_RECEIVER);
                }

                state = I2C_STATE_CLEAR_ADDRESS;
                timeout = 0;
                break;

            case I2C_STATE_CLEAR_ADDRESS:
                /* wait for address to be acknowledged */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_ADDSEND)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                if (write_phase) {
                    /* clear address flag (write phase) */
                    i2c_flag_clear(I2C0, I2C_FLAG_ADDSEND);
                    state = I2C_STATE_TRANSMIT_DATA;
                } else {
                    /* READ phase for 2 bytes: set POS=NEXT and disable ACK BEFORE clearing ADDR */
                    i2c_ackpos_config(I2C0, I2C_ACKPOS_NEXT);
                    i2c_ack_config(I2C0, I2C_ACK_DISABLE);

                    /* now clear address flag to release SCL and enter data phase */
                    i2c_flag_clear(I2C0, I2C_FLAG_ADDSEND);

                    state = I2C_STATE_RECEIVE_DATA;
                }

                timeout = 0;
                break;

            case I2C_STATE_TRANSMIT_DATA:
                /* wait for transmit buffer to be empty */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_TBE)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* send register address */
                i2c_data_transmit(I2C0, reg_addr);
                state = I2C_STATE_RESTART;
                timeout = 0;
                break;

            case I2C_STATE_RESTART:
                /* wait for byte transfer complete  BTC: Bit Transfer Complete */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_BTC)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* generate repeated start condition */
                i2c_start_on_bus(I2C0);
                
                /* wait for repeated start condition to be sent */
                timeout = 0;
                while ((!i2c_flag_get(I2C0, I2C_FLAG_SBSEND)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* send slave address with read bit (R/W bit is set by library) */
                i2c_master_addressing(I2C0, (slave_addr << 1), I2C_RECEIVER);

                /* switch to read phase */
                write_phase = false;
                state = I2C_STATE_CLEAR_ADDRESS;
                timeout = 0;
                break;

            case I2C_STATE_RECEIVE_DATA:
                /* Wait for BTC (both bytes received) */
                while ((!i2c_flag_get(I2C0, I2C_FLAG_BTC)) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* Send STOP before reading the last two bytes */
                i2c_stop_on_bus(I2C0);

                /* Read the two bytes back-to-back */
                data[0] = i2c_data_receive(I2C0);
                data[1] = i2c_data_receive(I2C0);

                state = I2C_STATE_STOP;
                break;

            case I2C_STATE_STOP:
                /* wait for stop condition to complete */
                while ((I2C_CTL0(I2C0) & I2C_CTL0_STOP) && (timeout < I2C_TIME_OUT)) {
                    timeout++;
                }
                if (timeout >= I2C_TIME_OUT) {
                    state = I2C_STATE_ERROR;
                    break;
                }

                /* i2c master sends STOP signal successfully */
                /* success */
                return I2C_RESULT_SUCCESS;

            case I2C_STATE_ERROR:
                /* send stop condition to release bus */
                i2c_stop_on_bus(I2C0);

                retry_count++;
                if (retry_count >= I2C_MAX_RETRY) {
#ifdef DEBUG_VERBOES
                    printf("IIC read failed after %d retries\n", I2C_RETRY_MAX);
#endif
                    return I2C_RESULT_ERROR;
                }

                /* reset state machine for retry */
                state = I2C_STATE_START;
                write_phase = true;
                timeout = 0;

                /* small delay before retry */
                delay_10us(10);
                break;

            default:
                state = I2C_STATE_START;
                break;
        }
    }
    return I2C_RESULT_TIMEOUT;
}

#ifdef DEBUG_VERBOSE
/*!
    \brief      get status string for debugging
    \param[in]  status: i2c_status_t value
    \param[out] none
    \retval     const char* status string
*/
const char* i2c_get_status_string(i2c_result_t status) {
    switch (status) {
        case I2C_RESULT_SUCCESS:
            return "SUCCESS";
        case I2C_RESULT_TIMEOUT:
            return "TIMEOUT";
        case I2C_RESULT_NACK:
            return "NACK";
        case I2C_RESULT_BUS_BUSY:
            return "BUS_BUSY";
        case I2C_RESULT_ERROR:
            return "ERROR";
        case I2C_RESULT_INVALID_PARAM:
            return "INVALID_PARAM";
        default:
            return "UNKNOWN";
    }
}
#endif