I2C子系统之驱动SSD1306 OLED
Posted hackfun
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理解I2C设备驱动框架，主要围绕四个结构体去分析就容易了。
struct i2c_algorithm：提供I2C协议的实现的操作，如：master_xfer实现数据收发的最基本方法。
struct i2c_adapter：每一个i2c_adapter都代表一个I2C物理接口，一个cpu可以有多个I2C接口（i2c_adapter），i2c_algorithm就是为i2c_adapter提供I2C协议的实现。每增加一个i2c接口，即是向i2c_bus_type (i2c_core.c)注册一个i2c_adapter
struct i2c_driver：代表着一类I2C从机设备的驱动，比如：at24cxx的驱动，不同类型的I2C从机需要注册不同的i2c_driver，如：ssd1306的驱动不同于at24cxx的驱动。每增加一个类型的I2C从机设备，都要向i2c_bus_type (i2c_core.c)注册一个i2c_driver
struct i2c_client：代表具体的某一个I2C从机设备，如：at24cxx系列的设备，有at24c01，at24c02等，每增加一个at24cxx设备，都要注册一个i2c_client。只有I2C从机设备被探测到，i2c_client才会被注册。
这四者的关系可以分为：i2c_algorithm和i2c_adapter一起驱动I2C总线，i2c_driver和i2c_client一起实现设备驱动。
注：linux目前只支持I2C主机模式。本文引用内核源码中i2c-algo-bit.c和i2c-gpio.c文件来讲解， i2c_driver由驱动开发者根据特定的设备提供，这里引用作者提供的ssd1306.c。i2c-algo-bit.c和i2c-gpio.c共同实现IO模拟I2C。
i2c-algo-bit.c提供了一个i2c_algorithm，i2c-gpio.c提供了一个i2c_adapter。
i2c-algo-bit.c通过以下代码绑定到i2c-gpio.c
i2c-algo-bit.c
1 static const struct i2c_algorithm i2c_bit_algo = { 2 .master_xfer = bit_xfer, 3 .functionality = bit_func, 4 }; 5 6 static int i2c_bit_prepare_bus(struct i2c_adapter *adap) 7 { 8 ... ... 9 adap->algo = &i2c_bit_algo; 10 ... ... 11 return 0; 12 } 13 14 int i2c_bit_add_bus(struct i2c_adapter *adap) 15 { 16 ... ... 17 err = i2c_bit_prepare_bus(adap); 18 ... ... 19 return i2c_add_adapter(adap); 20 }
i2c-gpio.c
1 static int __init i2c_gpio_probe(struct platform_device *pdev) 2 { 3 struct i2c_gpio_platform_data *pdata; 4 struct i2c_algo_bit_data *bit_data; 5 struct i2c_adapter *adap; 6 ... ... 7 pdata = pdev->dev.platform_data; 8 ... ... 9 i2c_bit_add_bus(adap); 10 ... ... 11 }
这里就注册了一个i2c_adapter。
要驱动ssd1306，因此对应地要提供一个i2c_driver，与i2c_adapter建立关系。
ssd1306.c
1 static struct i2c_driver ssd1306_driver = { 2 .driver = { 3 .name = "ssd1306", 4 }, 5 .id = I2C_DRIVERID_I2CDEV, 6 .attach_adapter = ssd1306_attach_adapter, 7 .detach_client = ssd1306_detach_client, 8 }; 9 10 static int ssd1306_module_init(void) 11 { 12 i2c_add_driver(&ssd1306_driver); 13 return 0; 14 }
i2c_driver和i2c_adapter是怎样建立关系的呢？
i2c_bus_type (i2c_core.c)负责桥接i2c_driver和i2c_adapter建立关系，在i2c_driver和i2c_adapter注册的时候，两者都会调用driver->attach_adapter(adapter)
1 int i2c_register_driver(struct module *owner, struct i2c_driver *driver) 2 { 3 ... ... 4 driver->attach_adapter(adapter); 5 ... ... 6 return 0; 7 } 8 9 static int i2c_register_adapter(struct i2c_adapter *adap) 10 { 11 ... ... 12 driver->attach_adapter(adap); 13 ... ... 14 }
driver->attach_adapter(adapter)实际上调用
1 static int ssd1306_attach_adapter(struct i2c_adapter *adapter) 2 { 3 return i2c_probe(adapter, &addr_data, ssd1306_detect); 4 }
I2c_probe()函数的作用就是，探测是否存在ssd1306这个设备，是怎样探测的呢？就是通过发送从机地址到ssd1306，如果ssd1306返回应答信号，就认为探测到了。
1 int i2c_probe(struct i2c_adapter *adapter, 2 struct i2c_client_address_data *address_data, 3 int (*found_proc) (struct i2c_adapter *, int, int)) 4 { 5 ... ... 6 i2c_probe_address(adapter, 7 address_data->probe[i + 1], 8 -1, found_proc); 9 ... ... 10 }
代码太多，简化函数调用关系如下：
1 i2c_probe_address() 2 i2c_smbus_xfer() 3 i2c_smbus_xfer_emulated(); 4 i2c_transfer(); 5 adap->algo->master_xfer(adap,msgs,num);
adap->algo->master_xfer(adap,msgs,num);实际调用的是bit_xfer()
探测到ssd1306后，其实也就说明了探测到的I2C地址有效， 还需要注册一个描述SSD1306的i2c_client。
1 static int ssd1306_detect(struct i2c_adapter *adapter, int address, int kind) 2 { 3 printk("ssd1306_detect\\n"); 4 5 ssd1306_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL); 6 ssd1306_client->addr = address; 7 ssd1306_client->adapter = adapter; 8 ssd1306_client->driver = &ssd1306_driver; 9 strcpy(ssd1306_client->name, "ssd1306"); 10 11 i2c_attach_client(ssd1306_client); 12 13 ... ... 14 }
先转下话题。
在i2c-gpio.c中，
1 static int __init i2c_gpio_init(void) 2 { 3 ... ... 4 ret = platform_driver_probe(&i2c_gpio_driver, i2c_gpio_probe); 5 ... ... 6 }
这里实际上是注册了一个platform_driver，我们还要对应的为他注册一个platform_device，
这个platform_device提供了硬件相关的设置，如指定那两个io口为SCL和SDA。
I2c_gpio_dev.c中
1 static struct i2c_gpio_platform_data i2c_dev = { 2 .sda_pin = S3C2410_GPG6, 3 .scl_pin = S3C2410_GPG5, 4 .udelay = 0, 5 .timeout = 0, 6 .sda_is_open_drain = 1, 7 .scl_is_open_drain = 1, 8 .scl_is_output_only = 1 9 }; 10 11 static struct platform_device i2c_platform_dev = { 12 .name = "i2c-gpio", 13 .id = -1, 14 .dev = { 15 .release = i2c_dev_release, 16 .platform_data = (void *)&i2c_dev, 17 }, 18 }; 19 20 static int i2c_dev_init(void) 21 { 22 platform_device_register(&i2c_platform_dev); 23 return 0; 24 }
如果platform_device和platform_driver匹配，就会调用i2c_gpio_probe()
1 static int __init i2c_gpio_probe(struct platform_device *pdev) 2 { 3 struct i2c_gpio_platform_data *pdata; 4 struct i2c_algo_bit_data *bit_data; 5 struct i2c_adapter *adap; 6 ... ... 7 pdata = pdev->dev.platform_data; 8 ... ... 9 i2c_bit_add_bus(adap); 10 ... ... 11 }
只有platform_device和platform_driver匹配才能注册i2c_adapter。
到这里，就可以操作ssd1306了。ssd1306写一个字节的操作：
1 static void ssd1306_write_byte(uint8_t chData, uint8_t chCmd) 2 { 3 uint8_t cmd = 0x00; 4 5 if (chCmd) { 6 cmd = 0x40; 7 } else { 8 cmd = 0x00; 9 } 10 11 i2c_smbus_write_byte_data(ssd1306_client, cmd, chData); 12 }
实际上调用了i2c_smbus_write_byte_data()
I2c_core.c提供了几个I2C的读写函数：
1 s32 i2c_smbus_write_byte_data(struct i2c_client *client, u8 command, u8 value); 2 s32 i2c_smbus_read_word_data(struct i2c_client *client, u8 command); 3 ... ... 4 s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client, u8 command, u8 *values); 5 s32 i2c_smbus_write_i2c_block_data(struct i2c_client *client, u8 command, 6 u8 length, const u8 *values)
运行代码
注：由于源码的i2c-gpio-bit.c只支持具有开漏输入输出功能的IO模拟I2C， 而我的开发板已经没有具有开漏输入输出功能的IO了，只能使用普通的上啦输入输出IO，对SDA的读写操作，需要切换输入输出方向。因此我把i2c-gpio-bit.c改成普通IO操作SDA，命名为my-i2c-gpio-bit.c，同时i2c-gpio-bit.h和i2c-gpio.c也要做相应改动，分别改为my-i2c-gpio-bit.h和my-i2c-gpio.c。如果使用具有开漏输入输出功能的IO，可以直接使用i2c-gpio-bit.c，i2c-gpio-bit.h，i2c-gpio.c。
代码
i2c_gpio_dev.c
1 #include <linux/module.h> 2 #include <linux/version.h> 3 4 #include <linux/init.h> 5 6 #include <linux/kernel.h> 7 #include <linux/types.h> 8 #include <linux/interrupt.h> 9 #include <linux/list.h> 10 #include <linux/timer.h> 11 #include <linux/init.h> 12 #include <linux/serial_core.h> 13 #include <linux/platform_device.h> 14 #include <linux/gpio_keys.h> 15 #include <linux/input.h> 16 #include <linux/irq.h> 17 #include <linux/i2c-gpio.h> 18 19 #include <asm/gpio.h> 20 #include <asm/io.h> 21 #include <asm/arch/regs-gpio.h> 22 23 24 /* [cgw]: */ 25 26 static struct i2c_gpio_platform_data i2c_dev = { 27 .sda_pin = S3C2410_GPG6, 28 .scl_pin = S3C2410_GPG5, 29 .udelay = 0, 30 .timeout = 0, 31 .sda_is_open_drain = 1, 32 .scl_is_open_drain = 1, 33 .scl_is_output_only = 1 34 }; 35 36 static void i2c_dev_release(struct device * dev) 37 { 38 printk("i2c_dev_release! \\n"); 39 } 40 41 /* [cgw]: 分配一个平台设备 */ 42 static struct platform_device i2c_platform_dev = { 43 .name = "i2c-gpio", 44 .id = -1, 45 .dev = { 46 .release = i2c_dev_release, 47 .platform_data = (void *)&i2c_dev, 48 }, 49 }; 50 51 52 static int i2c_dev_init(void) 53 { 54 /* [cgw]: 注册i2c_platform_dev平台设备 */ 55 platform_device_register(&i2c_platform_dev); 56 return 0; 57 } 58 59 static void i2c_dev_exit(void) 60 { 61 /* [cgw]: 注销i2c_platform_dev平台设备 */ 62 platform_device_unregister(&i2c_platform_dev); 63 } 64 65 module_init(i2c_dev_init); 66 module_exit(i2c_dev_exit); 67 68 MODULE_LICENSE("GPL");
ssd1306.c
1 #include <linux/kernel.h> 2 #include <linux/init.h> 3 #include <linux/module.h> 4 #include <linux/slab.h> 5 #include <linux/jiffies.h> 6 #include <linux/i2c.h> 7 #include <linux/mutex.h> 8 #include <linux/fs.h> 9 #include <asm/uaccess.h> 10 11 12 #define SSD1306_CMD 0 13 #define SSD1306_DAT 1 14 15 #define SSD1306_WIDTH 128 16 #define SSD1306_HEIGHT 64 17 18 static uint8_t s_chDispalyBuffer[128][8]; 19 20 const uint8_t c_chFont1608[95][16] = { 21 {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},/*" ",0*/ 22 {0x00,0x00,0x00,0x00,0x00,0x00,0x1F,0xCC,0x00,0x0C,0x00,0x00,0x00,0x00,0x00,0x00},/*"!",1*/ 23 {0x00,0x00,0x08,0x00,0x30,0x00,0x60,0x00,0x08,0x00,0x30,0x00,0x60,0x00,0x00,0x00},/*""",2*/ 24 {0x02,0x20,0x03,0xFC,0x1E,0x20,0x02,0x20,0x03,0xFC,0x1E,0x20,0x02,0x20,0x00,0x00},/*"#",3*/ 25 {0x00,0x00,0x0E,0x18,0x11,0x04,0x3F,0xFF,0x10,0x84,0x0C,0x78,0x00,0x00,0x00,0x00},/*"$",4*/ 26 {0x0F,0x00,0x10,0x84,0x0F,0x38,0x00,0xC0,0x07,0x78,0x18,0x84,0x00,0x78,0x00,0x00},/*"%",5*/ 27 {0x00,0x78,0x0F,0x84,0x10,0xC4,0x11,0x24,0x0E,0x98,0x00,0xE4,0x00,0x84,0x00,0x08},/*"&",6*/ 28 {0x08,0x00,0x68,0x00,0x70,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},/*"\'",7*/ 29 {0x00,0x00,0x00,0x00,0x00,0x00,0x07,0xE0,0x18,0x18,0x20,0x04,0x40,0x02,0x00,0x00},/*"(",8*/ 30 {0x00,0x00,0x40,0x02,0x20,0x04,0x18,0x18,0x07,0xE0,0x00,0x00,0x00,0x00,0x00,0x00},/*")",9*/ 31 {0x02,0x40,0x02,0x40,0x01,0x80,0x0F,0xF0,0x01,0x80,0x02,0x40,0x02,0x40,0x00,0x00},/*"*",10*/ 32 {0x00,0x80,0x00,0x80,0x00,0x80,0x0F,0xF8,0x00,0x80,0x00,0x80,0x00,0x80,0x00,0x00},/*"+",11*/ 33 {0x00,0x01,0x00,0x0D,0x00,0x0E,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},/*",",12*/ 34 {0x00,0x00,0x00,0x80,0x00,0x80,0x00,0x80,0x00,0x80,0x00,0x80,0x00,0x80,0x00,0x80},/*"-",13*/ 35 {0x00,0x00,0x00,0x0C,0x00,0x0C,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00},/*".",14*/ 36 {0x00,0x00,0x00,0x06,0x00,0x18,0x00,0x60,0x01,0x80,0x06,0x00,0x18,0x00,0x20,0x00},/*"/",15*/ 37 {0x00,0x00,0x07,0xF0,0x08,0x08,0x10,0x04,0x10,0x04,0x08,0x08,0x07,0xF0,0x00,0x00},/*"0",16*/ 38 {0x00,0x00,0x08,0x04,0x08,0x04,0x1F,0xFC,0x00,0x04,0x00,0x04,0x00,0x00,0x00,0x00},/*"1",17*/ 39 {0x00,0x00,0x0E,0x0C,0x10,0x14,0x10,0x24,0x10,0x44,0x11,0x84,0x0E,0x0C,0x00,0x00},/*"2",18*/ 40 {0x00,0x00,0x0C,0x18,0x10,0x04,0x11,0x04,0x11,0x04,0x12,0x88,0x0C,0x70,0x00,0x00},/*"3",19*/ 41 {0x00,0x00,0x00,0xE0,0x03,0x20,0x04,0x24,0x08,0x24,0x1F,0xFC,0x00,0x24,0x00,0x00},/*"4",20*/ 42 {0x00,0x00,0x1F,0x98,0x10,0x84,0x11,0x04,0x11,0x04,0x10,0x88,0x10,0x70,0x00,0x00},/*"5",21*/ 43 {0x00,0x00,0x07,0xF0,0x08,0x88,0x11,0x04,0x11,0x04,0x18,0x88,0x00,0x70,0x00,0x00},/*"6",22*/ 44 {0x00,0x00,0x1C,0x00,0x10,0x00,0x10,0xFC,0x13,0x00,0x1C,0x00,0x10,0x00,0x00,0x00},/*"7",23*/ 45 {0x00,0x00以上是关于I2C子系统之驱动SSD1306 OLED的主要内容，如果未能解决你的问题，请参考以下文章
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