#include "iic.h"

/* Software I2C delay (microseconds), based on SysTick */
static void delayUs(uint16_t us)
{
    uint32_t start = SysTick->VAL;
    uint32_t ticks = us * (SystemCoreClock / 1000000);

    if (start < ticks) {
        while (SysTick->VAL > start);
        while (SysTick->VAL < (SysTick->LOAD - (ticks - start)));
    } else {
        while ((SysTick->VAL < start) && (SysTick->VAL >= (start - ticks)));
    }
}

/* I2C Interface Initialization */
void iicInit(void)
{
    GPIO_InitTypeDef GPIO_InitStruct;

    __HAL_RCC_GPIOA_CLK_ENABLE();

    /* SDA - PA12, open-drain output */
    GPIO_InitStruct.Pin = SDA_Pin;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    HAL_GPIO_Init(SDA_GPIO_Port, &GPIO_InitStruct);

    /* SCL - PA11, push-pull output */
    GPIO_InitStruct.Pin = SCL_Pin;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    HAL_GPIO_Init(SCL_GPIO_Port, &GPIO_InitStruct);

    IIC_SCL_H;
    IIC_SDA_H;
}

/* I2C Start Signal */
void iicStart(void)
{
    IIC_SDA_H;
    IIC_SCL_H;
    delayUs(4);
    IIC_SDA_L;  /* SCL high, SDA high->low = start */
}

/* I2C Stop Signal */
void iicStop(void)
{
    IIC_SDA_L;
    IIC_SCL_H;
    delayUs(4);
    IIC_SDA_H;  /* SCL high, SDA low->high = stop */
}

/* Wait for ACK: returns 0=OK, 1=timeout */
uint8_t iicWaitAck(void)
{
    unsigned char timeout = 0;

    IIC_SDA_H;
    IIC_SCL_H;

    while (READ_SDA) {
        timeout++;
        if (timeout > 250) {
            iicStop();
            return 1;
        }
        delayUs(2);
    }
    IIC_SCL_L;
    delayUs(20);
    return 0;
}

/* Send One Byte (MSB first), return ACK status: 0=ACK, 1=NACK/timeout */
uint8_t iicSendByteAck(uint8_t txd)
{
    unsigned char t;

    IIC_SCL_L;
    for (t = 0; t < 8; t++) {
        IIC_SDA_OUT(((txd & 0x80) >> 7));
        txd <<= 1;
        delayUs(2);
        IIC_SCL_H;
        delayUs(2);
        IIC_SCL_L;
    }
    return iicWaitAck();
}

/* Send One Byte (MSB first), legacy API without ACK return */
void iicSendByte(uint8_t txd)
{
    (void)iicSendByteAck(txd);
}

/* Read One Byte; ack=1 send ACK, ack=0 send NACK */
unsigned char iicReadByte(uint8_t ack)
{
    unsigned char i;
    unsigned char receive = 0;

    IIC_SCL_L;
    delayUs(20);
    for (i = 0; i < 8; i++) {
        IIC_SCL_H;
        delayUs(20);
        receive <<= 1;
        if (READ_SDA) receive++;
        delayUs(20);
        IIC_SCL_L;
        delayUs(20);
    }

    if (!ack) {
        /* NACK */
        IIC_SDA_H;
        IIC_SCL_H;
        delayUs(2);
        IIC_SCL_L;
    } else {
        /* ACK */
        IIC_SDA_L;
        IIC_SCL_H;
        delayUs(2);
        IIC_SCL_L;
        IIC_SDA_H;
    }
    return receive;
}