作者：华清远见讲师
使用资料：i2c总线时序手册、24c02手册及ARM主芯片的datasheet
一、通过原理图查看i2c的sda/scl两个引脚连接到ARM主芯片的哪两个GPIO口，以我现在使用的单板为例，如下图
从此图可以看出连接的GPIO口为9_3、9_2两个引脚。
二、通过控制GPIO高低电平来模拟I2C的时序完成总线驱动
首先通过i2c时序手册可以查看到如下图的一个时序
使用gpio9_2 和gpio9_3两个引脚来模拟sda/scl的时序，核心代码如下：
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、编写测试程序i2c_read/i2c_write工具调用gpio_i2c_write/read操作24c02的基地址，基地址通过原理图来查看地址是为0xa0-0xae(这个地址是通过24c02的手册查看)中的哪一个，测试通过后进行24c02驱动的接口编写，若不通过需要查看sda/scl两根引脚是否正常上拉，连接是否有问题等。
从上面的原理图可以看出A0-A2均为接地，所以A0-A2的值全为0，再根据24c02的手册可以查出下图的slave address，值为0xa0。
四、编写24c02接口，并完成整个驱动的调试。