linux平台上GPIO模拟I2C

      GPIO模拟I2C是嵌入式中较为常用的一种应用。各个地方有各种不同的做法，按照我自己的个人理解，最好是把I2C的各种状态分割开来，比如起始条件终止条件，读数据和写数据，然后根据具体的使用场合组合起来。

      这里需要注意两点：一是SCL的波形并不规律，不能将它理解为方波，它本身只是一段段独立的波形。二是每段操作时，之前和之后的SCL和SDA波形是可以忽略的；通常情况下I2C开始之前和I2C结束之后，两者都是有上拉的高电平，而在正常工作时两者不受控制的情况下都是默认低电平。三是I2C是要默认外部上拉的，但是不能有内部上拉也就是必须内部下拉，否则会出现I2C传输时的错误。

（1）基础宏定义

#define GPIO_SCL S3C2410_GPF3
#define GPIO_SDA S3C2410_GPF0
#define GPIO_SDA_OUTP S3C2410_GPF0_OUTP //设定SDA输出
#define GPIO_SDA_INP S3C2410_GPF0_INP //设定SDA输入
#define GPIO_SCL_OUTP S3C2410_GPF3_OUTP //设定SCL输出

void I2C_SCL_OUTP( void )
{
s3c2410_gpio_cfgpin(GPIO_SCL,GPIO_SCL_OUTP);
}

void I2C_SCL_Output(u8 value)
{
if(value)
{
s3c2410_gpio_setpin(GPIO_SCL,value);
}
else
{
s3c2410_gpio_setpin(GPIO_SCL,value );
}
}

void I2C_SDA_Mode(u8 v_mode) //SDA输出方向
{
if(v_mode)
{
s3c2410_gpio_cfgpin(GPIO_SDA, GPIO_SDA_OUTP);
}
else
{
s3c2410_gpio_cfgpin(GPIO_SDA, GPIO_SDA_INP);
}
}

void I2C_SDA_Output(u8 value)
{
if(value)
{
s3c2410_gpio_setpin(GPIO_SDA,value);
}
else
{
s3c2410_gpio_setpin(GPIO_SDA,value );
}
}

u8 I2C_SDA_Read(void) //SDA读数据
{
return s3c2410_gpio_getpin(GPIO_SDA);
}

（2）基础段

void I2C_Init(void)
{
I2C_SDA_Output(1);
I2C_SCL_Output(1); //默认拉高
}

void I2C_Wait(void)
{
u16 i;
for(i=0;i<200;i++);
}

void I2C_Start(void)
{
I2C_SDA_Output(1);
I2C_SCL_Output(1);
I2C_Wait();
I2C_SDA_Output(0);
I2C_Wait();
I2C_SCL_Output(0);
}
void I2C_Stop(void)
{
I2C_SDA_Output(0);
I2C_Wait();
I2C_SCL_Output(1);
I2C_Wait();
I2C_SDA_Output(1);
}

（3）读写单个字节的段

u8 I2C_Send_Byte(u8 bytedata)
{
u8 i,ack;
I2C_SDA_Mode(1); //SDA输出
I2C_SCL_OUTP();
for (i = 0; i < 8; i++)
{
if (bytedata & 0x80)
{
I2C_SDA_Output(1);
}
else
{
I2C_SDA_Output(0);
}
bytedata <<= 1;

I2C_SCL_Output(1);
udelay(3);
I2C_SCL_Output(0);
udelay(1);
}

I2C_SDA_Output(1); //release
udelay(3);

I2C_SDA_Mode(0); //设定SDA输入
I2C_SCL_Output(1);
udelay(3);
ack = I2C_SDA_Read(); //读应答
I2C_SDA_Mode(1);
I2C_SCL_Output(0);
udelay(3);

return ack;
}

u8 I2C_Receive_Byte(void)
{
u8 i;
u8 bytedata = 0x00;
u8 temp;

I2C_SDA_Mode(0);
for ( i = 0; i < 8; i++)
{
I2C_SCL_Output(1);
udelay(3);

bytedata <<= 1;
temp = I2C_SDA_Read();
printk("reda SDA'value is:%d/n",temp);

if (temp)
bytedata |= 0x01;
printk(" bytedata is:%x/n",bytedata);
I2C_SCL_Output(0);
udelay(1);
}
I2C_SDA_Mode(1);
return bytedata;
}

（4）读写单个字节的I2C应用函数

u8 I2C_Byte_Write(u8 device_ID,u8 address,u8 bytedata)
{
u8 ack;
printk("device_ID is:%x/n",device_ID);
printk("address is:%x/n",address);
printk("date is:%x/n",bytedata);
I2C_Start();
ack=I2C_Send_Byte(device_ID);
printk("ack is:%d/n",ack);
if(ack)

I2C_Stop();
I2C_Send_Byte(address);
I2C_Send_Byte(bytedata);
I2C_Stop();
I2C_Wait();
return 0;
}

u8 I2C_Byte_Read(u8 device_ID,u8 address)
{
u8 bytedata;

I2C_Start();
I2C_Send_Byte(device_ID);
I2C_Send_Byte(address);
I2C_Start();
I2C_Send_Byte(device_ID+1);
bytedata = I2C_Receive_Byte(); //读单个字节，不需要再发应答
I2C_Stop();
return bytedata;
}

（5）类似可以完成读写多个字节的函数，暂不补充。


==================================================================================================================================

==================================================================================================================================

第二种方式也可以用

#ifdef I2C_USE_GPIO
#define GPIO_I2C_DEBUG

#define GPIO_I2C_SDA_PIN   GPIO_I2C1_SCA_PIN
#define GPIO_I2C_SCA_PIN   GPIO_I2C1_SDA_PIN
#define GPIO_SDA_OUTP   mt_set_gpio_dir(GPIO_I2C_SDA_PIN,GPIO_DIR_OUT)  //设定SDA输出
#define GPIO_SDA_INP      mt_set_gpio_dir(GPIO_I2C_SDA_PIN,GPIO_DIR_IN)     //设定SDA输入
#define GPIO_SCL_OUTP   mt_set_gpio_dir(GPIO_I2C_SCA_PIN,GPIO_DIR_OUT)  //设定SCL输出

#define I2C_SDA_Output(value)  mt_set_gpio_out(GPIO_I2C_SDA_PIN,value)
#define I2C_SCL_Output(value)  mt_set_gpio_out(GPIO_I2C_SCA_PIN,value)

#define DELAY_TIME   0xc0

u8 I2C_SDA_Read(void)    //SDA读数据
{
return mt_get_gpio_in(GPIO_I2C_SDA_PIN);
}

void I2C_Init(void)
{
mt_set_gpio_mode(GPIO_I2C_SDA_PIN,GPIO_MODE_00);
mt_set_gpio_mode(GPIO_I2C_SCA_PIN,GPIO_MODE_00);

GPIO_SDA_OUTP;
GPIO_SCL_OUTP;

I2C_SDA_Output(1);
I2C_SCL_Output(1);      //默认拉高
}

#define I2C_START_TRANSMISSION \
{ \
volatile u8 idx; \
GPIO_SCL_OUTP; \
GPIO_SDA_OUTP; \
I2C_SDA_Output(1); \
for (idx = 0; idx < DELAY_TIME; idx++); \
I2C_SCL_Output(1); \
for (idx = 0; idx < DELAY_TIME; idx++); \
I2C_SDA_Output(0); \
for (idx = 0; idx < DELAY_TIME; idx++); \
I2C_SCL_Output(0); \
}

#define I2C_STOP_TRANSMISSION \
{ \
volatile u8 idx; \
GPIO_SCL_OUTP; \
GPIO_SDA_OUTP; \
I2C_SCL_Output(0); \
I2C_SDA_Output(0); \
for (idx = 0; idx < DELAY_TIME; idx++); \
I2C_SCL_Output(1); \
for (idx = 0; idx < DELAY_TIME; idx++); \
I2C_SDA_Output(1); \
}

static kal_uint8 I2C_Send_Byte(kal_uint8 send_byte)
{
volatile signed char i = 0;
volatile kal_uint16 j = 0;
kal_uint8 ack = 0;

for (i = 7; i >= 0; i--)
{
if (send_byte&(1 << i))
{
I2C_SDA_Output(1);
}
else
{
I2C_SDA_Output(0);
}
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0; j < DELAY_TIME; j++);
GPIO_SDA_OUTP; /* only for delay */
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0; j < DELAY_TIME; j++);
}
GPIO_SDA_INP;
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0; j < DELAY_TIME; j++);
ack = I2C_SDA_Read();
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0; j < DELAY_TIME; j++);
GPIO_SDA_OUTP;

return ack;
}

static kal_uint8 I2C_Receive_Byte(void)
{
volatile signed char i = 0;
volatile kal_uint16 j = 0;
kal_uint8 get_byte = 0;

GPIO_SDA_INP;

for (j = 0; j < DELAY_TIME; j++);

for (i = 7; i >= 0; i--) {    // data bit 7~0
I2C_SCL_Output(1);
for (j = 0; j < DELAY_TIME; j++);
if (I2C_SDA_Read()) {
get_byte |= (1 << i);
}
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0; j < DELAY_TIME; j++);
}

// don't care bit, 9th bit
GPIO_SDA_OUTP;
I2C_SDA_Output(1);
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(0);

return get_byte;
}

static kal_uint16 I2C_Receive_word(void)
{
volatile signed char i = 0;
volatile kal_uint32 j = 0;
kal_uint16 get_byte = 0;

for (i = 15; i >= 8; i--)
{
GPIO_SDA_INP;
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0; j < DELAY_TIME; j++);
if (I2C_SDA_Read()) get_byte |= (1 << i);
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0; j < DELAY_TIME; j++);
}
I2C_SDA_Output(0);
GPIO_SDA_OUTP;
for (j = 0;j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0;j < DELAY_TIME; j++);
GPIO_SDA_OUTP; /* just for delay */
for (j = 0;j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0;j < DELAY_TIME; j++);
for (; i >= 0; i--)
{
GPIO_SDA_INP;
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0; j < DELAY_TIME; j++);
if (I2C_SDA_Read()) get_byte |= (1 << i);
for (j = 0; j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0; j < DELAY_TIME; j++);
}
I2C_SDA_Output(1);
GPIO_SDA_OUTP;
for (j = 0;j < DELAY_TIME; j++);
I2C_SCL_Output(1);
for (j = 0;j < DELAY_TIME; j++);
GPIO_SDA_OUTP; /* just for delay */
for (j = 0;j < DELAY_TIME; j++);
I2C_SCL_Output(0);
for (j = 0;j < DELAY_TIME; j++);

return get_byte;
}

u8 I2C_Byte_Write(u8 * a_puBuff , u8 len , u8 i2c_addr)
{
kal_uint8 fail_try_no = 4;
volatile signed char i = 0 ;
u8 ack_flag = 0;
while (--fail_try_no > 0)
{
ack_flag = 0;
I2C_START_TRANSMISSION;
if (I2C_Send_Byte(i2c_addr)) continue;
for(i = 0 ;i < len;i++){
if (I2C_Send_Byte(a_puBuff[i])){
ack_flag = 1;
break;
}
}
if(ack_flag)
continue;
break;
}
I2C_STOP_TRANSMISSION;
return 0;
}

u8 I2C_Bytes_Read(u8 *a_puBuff, u8 reglen ,u8 *byteget,u8 bytelen,u8 i2c_addr)
{

kal_uint16 get_byte = 0xFFFF;
kal_uint8 fail_try_no = 4;
volatile kal_uint32 i = 0;
u8 ack_flag = 0;

while (--fail_try_no > 0)
{
ack_flag = 0;
I2C_START_TRANSMISSION;
if (I2C_Send_Byte(i2c_addr)) continue;

//send reg
for(i = 0 ;i < reglen;i++){
if (I2C_Send_Byte(a_puBuff[i])){
ack_flag = 1;
break;
}
}
if(ack_flag)
continue;

I2C_START_TRANSMISSION;
if (I2C_Send_Byte(i2c_addr | 1)) continue;

if(bytelen == 1)
byteget[0] = get_byte = I2C_Receive_Byte();  //读单个字节，不需要再发应答
else if(bytelen > 1)
{
get_byte=I2C_Receive_word();
byteget[1] = get_byte & 0x00ff;
byteget[0] = (get_byte & 0xff00) >> 8;
}
break;
}
I2C_STOP_TRANSMISSION;

printk("----%s---read data %x---\n",__func__,get_byte);

return get_byte;

}

int iWriteRegI2C(u8 *a_pSendData , u16 a_sizeSendData, u16 i2cId)
{
I2C_Byte_Write(a_pSendData,a_sizeSendData,i2cId);
return 0;
}

int iReadRegI2C(u8 *a_pSendData , u16 a_sizeSendData, u8 * a_pRecvData, u16 a_sizeRecvData, u16 i2cId)
{
I2C_Bytes_Read(a_pSendData,a_sizeSendData,a_pRecvData,a_sizeRecvData,i2cId);
return 0;
}
#endif