I2C裸机驱动程序设计

① I2C（Inter-Integrated Circuit）总线是由飞利浦公司开发的两线式串行总线，用于连接微控制器及其外围设备

② I2C总线有两根双向信号线

（1）SDA：Serial Data Line（数据线）

（2）SCL：Serial CLock Line（时钟线）

③ I2C总线寻址

（1）I2C总线协议规定，从设备采用7位的地址。

　　* D7~D0：从设备地址

　　* D0位：数据的传送方向。“0”表示主设备向从设备写数据；“1”表示主设备由从设备读数据

　　注：主设备发送地址时，总线上的每个从设备都将这7位地址与自己的地址进行比较，如果相同，则认为是自己正被主设备寻址，根据R/W位将自己确定为发送器或者接收器

（2）从设备的地址由固定部分和用户自定义部分组成。

　　* 固定部分：D7-D4 共4位。这是由从设备的生产厂商生产时就已确定的值。

　　* 用户自定义部分：D3-D1 共3位。这3位通常对应设备的3个引脚(A0~A2)。把3个引脚接到不同的电平上，就可以形成一个3位的数值。

④ I2C总线时序

（1）空闲状态：I2C总线总线的SDA和SCL两条信号线同时处于高电平时，规定为总线的空闲状态。

（2）起始状态：在时钟线SCL保持高电平期间，数据线SDA上的电平被拉低（即负跳变），定义为I2C总线总线的启动信号，它标志着一次数据传输的开始

（3）结束状态：在时钟线SCL保持高电平时，数据线SDA被释放，使得SDA返回高电平（即正跳变），称为I2C总线的停止信号

（4）数据传送：I2C总线上的所有数据（地址和数据）都是以8位一个字节为单位传送的

（5）应答位：发送器每发送一个字节，就在时钟脉冲第9位释放数据线，由接收器反馈一个应答信号。应答信号为低电平时，定为有效应答位ACK,表示接收器已经成功地接收了该字节；应答信号为高电平时，定为非应答位（NACK），表示接收器没有成功接收该字节

　　注：I2C接口会在SCL为高电平期间对SDA状态进行采样，所以SDA高低位的变换应该在SCL是低电平期间完成。所以SDA的高电平脉冲要要比SCL略宽。

⑤ 基于S3C2440的I2C裸机代码：

#include "GlobalDefine.h"
#include "Error.h"
#include "Common.h"
#include "I2c.h"

#include "ModManager.h"
#include "../Protocol/inc/I2cProtocol.h"

#define INTPND (*(volatile unsigned long*)0x4a000010)
#define SRCPND (*(volatile unsigned long*)0x4a000000)
#define INTMSK (*(volatile unsigned long*)0x4a000008)
#define GPECON (*(volatile unsigned long*)0x56000040)
#define GPEUP  (*(volatile unsigned long*)0x56000048)

#define IICCON    (*(volatile unsigned char*)0x54000000)
#define IICSTAT   (*(volatile unsigned char*)0x54000004)
#define IICDS     (*(volatile unsigned char*)0x5400000C)

#define SLAVE_WRITE_ADDR 0xa0
#define SLAVE_READ_ADDR 0xa1

static void I2cDelay(int i)
{
   int j = 0;
   while (i--)    
   {
       for (j = 0; j < 100; j++)
       {    
           ;
       }  
   }    
}

static void I2cInit()
{
    //1 Interrupt Initialize
    INTPND |= (1 << 27);
    SRCPND |= (1 << 27);  
    INTMSK &= ~(1 << 27);
     
    IICCON |= (1 << 5); 
    
    //2 Set I2C-Bus transmit clock
    IICCON &= ~(1 << 6);
    IICCON &= ~(0xf << 0);
    IICCON |= (0x5 << 0);
    
    //3. Set IIC-bus data output enable
    IICSTAT |= (1 << 4);
    
    //4. Set GPIO pin function
    GPECON |= (0x2 << 28)|(0x2 << 30);
    GPEUP |= (0x3 << 14);
    
    //5. Set IIC-bus acknowledge enable
    IICCON |= (1 << 7);
}

static void I2cWriteByte(unsigned char data, unsigned char addr)
{    
    //1. Set to Master-Transmit mode
    IICSTAT |= (3 << 6);
    
    //2. Write slave device address
    IICDS = SLAVE_WRITE_ADDR;
    IICCON &= ~(1 << 4);
    
    //3. Write 0xF0 to IICSTAT.(Generate START signal) 
    IICSTAT = 0xF0;
    
    // Wait Ack
    while ((IICCON & (1 << 4)) == 0 )
        I2cDelay(100);
    
    //4. Write address in chip to IICDS
    IICDS = addr;
    IICCON &= ~(1 << 4);
    
    // Wait Ack
    while ((IICCON & (1 << 4)) == 0 )
        I2cDelay(100);
    
    //5. Write data to IICDS
    IICDS = data;
    IICCON &= ~(1 << 4);   
    
    // Wait Ack
    while ((IICCON & (1 << 4)) == 0 )
        I2cDelay(100);
    
    //6. Write 0xD0 to IICSTAT(Generate STOP signal)
    IICSTAT = 0xD0;
    
    //7. Clear Interrupt
    IICCON &= ~(1 << 4);    
    
    I2cDelay(100);
}

static void I2cReadBytes(unsigned char addr, int length, unsigned char *buf)
{
    int j = 0;
    unsigned char unusedata;
    
    //1. Set to Master-Transmit mode
    IICSTAT |= (3 << 6);
    
    //2. Write slave device write address
    IICDS = SLAVE_WRITE_ADDR;
    IICCON &= ~(1 << 4);
    
    //3. Write 0xF0 to IICSTAT
    IICSTAT = 0xF0;
    
    //Wait ACK
    while ((IICCON & (1 << 4)) == 0 )
        I2cDelay(100);
    
    //4. Write address in the eeprom
    IICDS = addr;
    IICCON &= ~(1 << 4);
    
    // Wait ACK
    while ((IICCON & (1 << 4)) == 0 )
        I2cDelay(100);
             
    //5. Set to Master-Receive mode
    IICSTAT &= ~(3 << 6);
    IICSTAT |= (2 << 6);
    
    //6. Write slave device read address
    IICDS = SLAVE_READ_ADDR;
    IICCON &= ~(1 << 4);
    
    //7. Write 0xB0 to IICSTAT for starting to receive
    IICSTAT = 0xb0;
    while ((IICCON & (1 << 4)) == 0 )
        I2cDelay(100);
    
    //8. Write address in chip
    IICDS = addr;
    IICCON &= ~(1 << 4);
    
    while((IICCON & (1 << 4)) == 0)
    {
        I2cDelay(100);
    }
  
    for(j = 0; j < length; j++)
    {
        if(j == (length - 1))
        {
           IICCON &= ~(1 << 7);         
        }
   
        buf[j] = IICDS;
        
        // Clear Interrupt
        IICCON &= ~(1 << 4);
    
        // Wait for Interrupt
        while ((IICCON & (1 << 4)) == 0 )
            I2cDelay(100);
    }
    
    //9. Write 0x90 to IICSTAT(Generate STOP signal)
    IICSTAT = 0x90;
    
    //10. Clear Interrupt
    IICCON &= ~(1 << 4);
}

I2cModeOps i2cModeOps = {
    .I2cInit = I2cInit,
    .I2cWriteByte = I2cWriteByte,
    .I2cReadBytes = I2cReadBytes,
};

MODULE_INSTALL(I2c, MOD_I2C, 0, &i2cModeOps);