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使用資料：i2c總線時序手冊、24c02手冊及ARM主芯片的datasheet

一、通過原理圖查看i2c的sda/scl兩個引腳連接到ARM主芯片的哪兩個GPIO口，以我現在使用的單板為例，如下圖

從此圖可以看出連接的GPIO口為9_3、9_2兩個引腳。

二、通過控制GPIO高低電平來模擬I2C的時序完成總線驅動

首先通過i2c時序手冊可以查看到如下圖的一個時序

使用gpio9_2 和gpio9_3兩個引腳來模擬sda/scl的時序，核心代碼如下：

Gpioi2c.c

#define SCL (1 <<3) /* GPIO 9_3 */

#define SDA (1 << 2) /* GPIO 9_2 */

#define GPIO_I2C_SDA_REG (GPIO_9_BASE + 0x10)

#define GPIO_I2C_SCL_REG (GPIO_9_BASE + 0x20)

#define GPIO_I2C_SCLSDA_REG (GPIO_0_BASE + 0x30)

#define HW_REG(reg) *((volatile unsigned int *)(reg))

/*

* I2C by GPIO simulated read data routine.

*

* @return value: a bit for read

*

*/

static unsigned char i2c_data_read(void)

{

unsigned char regvalue;

regvalue = HW_REG(GPIO_9_DIR);

regvalue &= (~SDA);

HW_REG(GPIO_9_DIR) = regvalue;

DELAY(1);

regvalue = HW_REG(GPIO_I2C_SDA_REG);

if((regvalue&SDA) != 0)

return 1;

else

return 0;

}

/*

* sends a start bit via I2C rountine.

*

*/

static void i2c_start_bit(void)

{

DELAY(1);

i2c_set(SDA | SCL);

DELAY(1);

i2c_clr(SDA);

DELAY(2);

}

/*

* sends a stop bit via I2C rountine.

*

*/

static void i2c_stop_bit(void)

{

/* clock the ack */

DELAY(1);

i2c_set(SCL);

DELAY(1);

i2c_clr(SCL);

/* actual stop bit */

DELAY(1);

i2c_clr(SDA);

DELAY(1);

i2c_set(SCL);

DELAY(1);

i2c_set(SDA);

DELAY(1);

}

/*

* sends a character over I2C rountine.

*

* @param c: character to send

*

*/

static void i2c_send_byte(unsigned char c)

{

int i;

// local_irq_disable();

for (i=0; i<8; i++)

{

DELAY(1);

i2c_clr(SCL);

DELAY(1);

if (c & (1<<(7-i)))

i2c_set(SDA);

else

i2c_clr(SDA);

DELAY(1);

i2c_set(SCL);

DELAY(1);

i2c_clr(SCL);

}

DELAY(1);

// i2c_set(SDA);

// local_irq_enable();

}

/* receives a character from I2C rountine.

*

* @return value: character received

*

*/

static unsigned char i2c_receive_byte(void)

{

int j=0;

int i;

unsigned char regvalue;

// local_irq_disable();

for (i=0; i<8; i++)

{

DELAY(1);

i2c_clr(SCL);

DELAY(2);

i2c_set(SCL);

regvalue = HW_REG(GPIO_9_DIR);

regvalue &= (~SDA);

HW_REG(GPIO_9_DIR) = regvalue;

DELAY(1);

if (i2c_data_read())

j+=(1<<(7-i));

DELAY(1);

i2c_clr(SCL);

}

// local_irq_enable();

DELAY(1);

// i2c_clr(SDA);

// DELAY(1);

return j;

}

/* receives an acknowledge from I2C rountine.

*

* @return value: 0--Ack received; 1--Nack received

*

*/

static int i2c_receive_ack(void)

{

int nack;

unsigned char regvalue;

DELAY(1);

regvalue = HW_REG(GPIO_9_DIR);

regvalue &= (~SDA);

HW_REG(GPIO_9_DIR) = regvalue;

DELAY(1);

i2c_clr(SCL);

DELAY(1);

i2c_set(SCL);

DELAY(1);

nack = i2c_data_read();

DELAY(1);

i2c_clr(SCL);

DELAY(1);

// i2c_set(SDA);

// DELAY(1);

if (nack == 0)

return 1;

return 0;

}

EXPORT_SYMBOL(gpio_i2c_read);

unsigned char gpio_i2c_read(unsigned char devaddress, unsigned char address)

{

int rxdata;

i2c_start_bit();

i2c_send_byte((unsigned char)(devaddress));

i2c_receive_ack();

i2c_send_byte(address);

i2c_receive_ack();

i2c_start_bit();

i2c_send_byte((unsigned char)(devaddress) | 1);

i2c_receive_ack();

rxdata = i2c_receive_byte();

//i2c_send_ack();

i2c_stop_bit();

return rxdata;

}

EXPORT_SYMBOL(gpio_i2c_write);

void gpio_i2c_write(unsigned char devaddress, unsigned char address, unsigned char data)

{

i2c_start_bit();

i2c_send_byte((unsigned char)(devaddress));

i2c_receive_ack();

i2c_send_byte(address);

i2c_receive_ack();

i2c_send_byte(data);

// i2c_receive_ack();//add by hyping for tw2815

i2c_stop_bit();

}

三、編寫測試程序i2c_read/i2c_write工具調用gpio_i2c_write/read操作24c02的基地址，基地址通過原理圖來查看地址是為0xa0-0xae(這個地址是通過24c02的手冊查看)中的哪一個，測試通過后進行24c02驅動的接口編寫，若不通過需要查看sda/scl兩根引腳是否正常上拉，連接是否有問題等。

從上面的原理圖可以看出A0-A2均為接地，所以A0-A2的值全為0，再根據24c02的手冊可以查出下圖的slave address，值為0xa0。

四、編寫24c02接口，并完成整個驅動的調試。