用Raspberry Pi 學Linux I2C Driver http://www.ittraining.com.tw/ittraining/course/embedded/devicedriver

1. LINUX I2C DEVICE DRIVER
在Raspberry Pi 上面學 Linux 驅動程式開發
1

2. I2C 簡介
24LC02 EEPROM 簡介
Linux I2C Driver Framework
I2C Client Driver FOR 24LC02
I2c Host Controller (Master Driver)
User Space Driver
Low-Level Sysfs Operations
Outline

3. 它是一種半雙工的串列式 bus
它是一種廣播式的 bus
三種通訊速度
1. Standard is 100 Kbps
2. Fast-mode is 400 Kbps
3. high-speed mode supports speeds up to 3.4
Mbps
supports 7-bit and 10-bit address
Master-slave communication
3
What is I2C (Inter-IC) ?

4. 4
硬體接線

5. 5
硬體訊號

6. 6
Start and Stop conditions
•

7. 7
Data format
• Every byte put on the SDA line must be 8-bits long.
• Each byte has to be followed by an acknowledge bit.

8. 8
Link level protocol

9. 艾鍗Raspberry Pi I/O 上的 Serial EEPROM

10. 24C02
2Kbit size (256x8bit) serial EEPROM
I2C interface
32 pages of 8 bytes each
SOIC-8
Serial EEPROM 規格與線路

11. 24C02 Write OPERATION
Page write operations are limited to writing bytes within a single physical page
Physical page boundaries start at addresses that are integer multiples of the page buffer size
(or ‘page size’) and end at addresses that are integer multiples of [page size – 1].

12. 12
24C02 READ OPERATION
Two groups of eight addresses (0000XXX and 1111XXX) are reserved for
the purposes

13. Linux I2C Driver Framework

14. 14
Software stack
User Applications
/sys
i2c-dev
i2c Driver
i2c Client Device
i2c Bus
User space
Kernel space
Hardware
/sys/device/platform/ i2c
/dev/i2c-0, /dev/i2c-1
i2c User space driver
i2c Client Device
i2c Driver
i2c-core
adapter-
Specific code
adapter-
Specific code
i2c
adapter
i2c
algorithm
i2c Host Controller
(adpter)

15. drivers/i2c – i2c的根目錄
1. busses – i2c adapter的驅動程式 (handle i2c bus)
2. i2c-core.c: i2c bus 通訊軟體層, 提供了client <-> adapter 通訊
3. I2c-dev.c 通用的 user space client driver for /dev/i2c-x
4. algos 實現了一些I2C adapter的algorithm,
algorithm 完成不同底層傳送控制方式, 如
I2C-Bus bit-banging algorithm (alog/i2c-algo-bit.c)
15
Linux i2C 程式檔案結構

16. I2C Client Driver FOR 24LC02

17. I2C Client Driver in Kernel
I2C Client
.type=“at24”
.address
=0x50
I2C Driver
static struct i2c_driver at24_driver = {
.driver = {
.name = “at24-eeprom", // name string only
.owner = THIS_MODULE,
},
.probe = at24_probe,
.remove = at24_remove,
//List of I2C devices supported by this driver
.id_table = at24_ids,
};
i2c_add_driver(&at24_driver);//i2c driver的註冊
…
一旦i2c_add_driver註冊成功, kernel call probe()函式(即 at24_probe)
at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
client : 表示找到的I2C Client 裝置 (即原註冊的i2c_board_info )
id : 表示在 .id_table 表格中找到對應的那一筆
.probe
i2c_add_driver(struct i2c_driver * ) struct i2c_device_id *id
I2C Adapter
SCL
SDA
I2C Host 負責底層i2c bus通訊
static struct i2c_board_info at24lc16[ ] = {
{
I2C_BOARD_INFO("at24", 0x50),
.platform_data = &bcm2708_eeprom_info,
.irq=xx
},
}; struct i2c_client *client
I2C Client
.type=“xxxx”
.address =0x??
I2C Bus
static const struct i2c_device_id at24_ids[] = {
{ "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },
{ "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },
....
{ "at24", 0 },
};
i2c_register_board_info(bus , i2c_board_info, )

18. id_table 主要是讓一個Driver 可以同時支援多個
設備驅動
.driver_data : 允許每個設備有不同的參數
• 和void * platform_data有異曲同工之處
.id_table
struct i2c_device_id {
char name[I2C_NAME_SIZE];
kernel_ulong_t driver_data /* data private to the driver */
__attribute__((aligned(sizeof(kernel_ulong_t))));
};

19. 加入到 /arm/mach-bcm2708/bcm2708.c
新增I2C Device for EEPROM
//------ADD EEPROM AT24 Device------------------
static void eeprom_init_setup(struct memory_accessor *mem_acc , void *context)
{
dprint("nDo init work for EEPROMn");
}
static struct at24_platform_data bcm2708_eeprom_info = { // EEPROM chip capability
.byte_len = (2*1024)/8, // 256byte (24LC02)
.page_size = 8, // page write 8 byte; see chip datasheet (15)
.setup = eeprom_init_setup,
.context = (void*)NULL,
};
static struct i2c_board_info __initdata at24lc16[] = {
{
I2C_BOARD_INFO("at24", 0x50), //name of device as well as slave addr.
.platform_data = &bcm2708_eeprom_info,
},
};
i2c_register_board_info(1,at24lc16, ARRAY_SIZE(at24lc16));

20. i2c_add_driver()
註冊 I2C Driver for i2c client

21. i2c-bus interface Header 定義:
include/linux/i2c.h
I2C Client device

22. i2c-bus interface Header 定義:
include/linux/i2c.h
struct i2c_driver — represent an I2C device driver
struct i2c_client — represent an I2C slave device
struct i2c_board_info — template for device creation
I2C_BOARD_INFO — macro used to list an i2c device and its
address
i2c_register_board_info — statically declare I2C devices
struct i2c_msg — an I2C transaction segment beginning with
START
i2c_transfer — execute a single or combined I2C message
i2c_add_driver — unregister I2C driver
i2c_del_driver — unregister I2C driver
void i2c_set_clientdata(struct i2c_client *dev, void *data)
void *i2c_get_clientdata(const struct i2c_client *dev)
Kernel API for I2C Driver
static inline void i2c_set_clientdata(struct i2c_client *dev, void *data)
{ dev_set_drvdata(&dev->dev, data); }
同platform_set_drvdata 及 platform_get_drvdata

23. 每一次的START就要包裝成一個i2c message, 然後用i2c_transfer()去送,
i2c_transfer()送完後就是STOP狀態
I2c Message Format
Example for write command
addr flags

24. i2c_transfer()
int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)
{
if (adap->algo->master_xfer) {
……..
ret = __i2c_transfer(adap, msgs, num);
….
} else {
dev_dbg(&adap->dev, "I2C level transfers not supportedn");
return -EOPNOTSUPP;
}
}
It depends on the implementation of
bus driver …….
(we will discuss later)

25. #include <linux/i2c.h>
struct i2c_msg for read example
static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf, unsigned offset, size_t count)
{
struct i2c_msg msg[2];
u8 msgbuf[2];
memset(msg, 0, sizeof(msg));
msgbuf[0] = offset;
msg[0].addr = client->addr;
msg[0].buf = msgbuf;
msg[0].len = 1;
msg[1].addr = client->addr;
msg[1].flags = I2C_M_RD;
msg[1].buf = buf;
msg[1].len = count;
status = i2c_transfer(client->adapter, msg, 2);
if (status == 2)
status = count;
…..
}

26. Low-Level Sysfs Operations for EEPROM

27. Low-Level Sysfs Operations
struct at24_data {
struct at24_platform_data chip;
struct mutex lock;
......
struct bin_attribute bin;
......
};
static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
……………..
sysfs_bin_attr_init(&at24->bin);
at24->bin.attr.name = “eeprom”; //file name
at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
at24->bin.read = at24_bin_read; // function pointer to read operation
at24->bin.size = chip.byte_len; //256byte
at24->bin.write = at24_bin_write; ; // function pointer to write operation
at24->bin.attr.mode |= S_IWUSR;
………
err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);
}
struct attribute {
char *name;
struct module *owner;
mode_t mode;
};
struct bin_attribute {
struct attribute attr;
size_t size;
ssize_t (*read)(struct kobject *kobj, char *buffer, loff_t pos, size_t size);
ssize_t (*write)(struct kobject *kobj, char *buffer, loff_t pos, size_t size);
};

28. ls –l /sys/bus/i2c/devices
User Applications 使用/sys
長出eerpom的bin檔案

29. 先修改 /arm/mach-bcm2708/bcm2708.c, 加
入I2C client Device (i2c board info)
範例程式:
cd Pi_driver11_I2C_eerpom
make
insmod at24.ko
ls –l /sys/bus/i2c/drivers, 顯示註冊的i2c driver
的名稱 “at24”
Hands on

30. EEPROM就像檔案一樣操作
> echo "ittraining" > eeprom
> hexedit eeprom
> cd /sys/bus/i2c/devices/1-0050
> dd if=/dev/zero of=eeprom count=256

31. I2C Message & Ioctl

32. i2c-bus driver, char device interface
• open (“/dev/i2c-1”)
/dev/i2c

33. #include <linux/i2c-dev.h >
i2c-dev.h

34. Example: see eeprom-i2c.c

35. 進入Pi_driver範例程式
1. cd Pi_driver/11_I2C_eerpom/i2c-dev
2. make
3. insmod i2c-dev.ko 產生 /dev/i2c-1
4. gcc eeprom-i2c.c –o eep
5. Execute ‘eep’ to read/write EEPROM
Hands on

36. i2cdetect -y 1
EEPROM read/write using i2cset/i2cget
Using i2c-tools

37. 37
Using i2c-tools

38. I2c Host Controller (Master Driver)

39. I2C Bus Driver (I2C Adapter driver)
Declare a
Platform Device
(describe BSC1)
Register a
Platform Driver
drivers/i2c/buses/i2c-bcm2708.c
int bcm2708_i2c_probe(struct platform_device *pdev)
{ ……….
struct i2c_adapter *adap;
struct bcm2708_i2c *bi;
/*platform_get_resource & get_irq* /
/*set pin to i2C function SDA &SCL* /
……..
bi = kzalloc(sizeof(*bi), GFP_KERNEL);
adap = &bi->adapter;
adap->class = I2C_CLASS_HWMON | I2C_CLASS_DDC;
adap->algo = &bcm2708_i2c_algorithm;
adap->algo_data = bi;
adap->dev.parent = &pdev->dev;
adap->nr = pdev->id;
strlcpy(adap->name, dev_name(&pdev->dev), sizeof(adap->name));
/* ioremap & request_irq */
/* haredware init */
……..
//declare i2c adapter, use static bus number
i2c_add_numbered_adapter (adap);
}
adapter-Specific
code
註冊一個
i2c adapter
i2c
algorithm
arch/arm/mach-bcm2708/bcm2708.c
struct platform_device *pdev
Probe
Linux I2C subsystem

40. arch/arm/mach-bcm2708/bcm2708.c
Platform Device Register
static struct platform_device bcm2708_bsc1_device = {
.name = "bcm2708_i2c",
.id = 1,
.num_resources = ARRAY_SIZE(bcm2708_bsc1_resources),
.resource = bcm2708_bsc1_resources
};
static struct resource bcm2708_bsc1_resources[] = {
{
.start = BSC1_BASE,
.end = BSC1_BASE + SZ_256 - 1,
.flags = IORESOURCE_MEM,
}, {
.start = INTERRUPT_I2C,
.end = INTERRUPT_I2C,
.flags = IORESOURCE_IRQ,
}
};
BCM2835 有3個I2C Host
controller
platform_device_register(&bcm2708_bsc1_device);

41. • struct i2c_adapter;
• struct algorithm;
• int i2c_add_numbered_adapter(struct i2c_adapter *adap);
• int i2c_del_adapter(struct i2c_adapter *adap)’
41
Kernel API for I2C Adapter (master)

42. 42
struct i2c_adapter
/*adapter number for a specific adapter*/

43. 43
struct i2c_algorithm

44. #define I2C_FUNC_I2C 0x00000001
#define I2C_FUNC_10BIT_ADDR 0x00000002
#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /* I2C_M_{REV_DIR_ADDR,NOSTART,..} */
#define I2C_FUNC_SMBUS_PEC 0x00000008
#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL 0x00008000 /* SMBus 2.0 */
#define I2C_FUNC_SMBUS_QUICK 0x00010000
#define I2C_FUNC_SMBUS_READ_BYTE 0x00020000
#define I2C_FUNC_SMBUS_WRITE_BYTE 0x00040000
#define I2C_FUNC_SMBUS_READ_BYTE_DATA 0x00080000
#define I2C_FUNC_SMBUS_WRITE_BYTE_DATA 0x00100000
#define I2C_FUNC_SMBUS_READ_WORD_DATA 0x00200000
#define I2C_FUNC_SMBUS_WRITE_WORD_DATA 0x00400000
#define I2C_FUNC_SMBUS_PROC_CALL 0x00800000
#define I2C_FUNC_SMBUS_READ_BLOCK_DATA 0x01000000
#define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000
#define I2C_FUNC_SMBUS_READ_I2C_BLOCK 0x04000000 /* I2C-like block xfer */
#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK 0x08000000 /* w/ 1-byte reg. addr. */
#define I2C_FUNC_SMBUS_READ_I2C_BLOCK_2 0x10000000 /* I2C-like block xfer */
#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK_2 0x20000000 /* w/ 2-byte reg. addr. */
#define I2C_FUNC_SMBUS_EMUL (I2C_FUNC_SMBUS_QUICK |
I2C_FUNC_SMBUS_BYTE |
I2C_FUNC_SMBUS_BYTE_DATA |
I2C_FUNC_SMBUS_WORD_DATA |
I2C_FUNC_SMBUS_PROC_CALL |
I2C_FUNC_SMBUS_WRITE_BLOCK_DATA |
I2C_FUNC_SMBUS_I2C_BLOCK |
I2C_FUNC_SMBUS_PEC
44
I2C Functionality List

45. arch/arm/mach-bcm2708/bcm2708.c
註冊 Platform Device for I2C Host
static struct platform_device bcm2708_bsc0_device = {
.name = "bcm2708_i2c",
.id = 0, // i2c-0
.num_resources = ARRAY_SIZE(bcm2708_bsc0_resources),
.resource = bcm2708_bsc0_resources
};
static struct resource bcm2708_bsc0_resources[] = {
{
.start = BSC0_BASE,
.end = BSC0_BASE + SZ_256 - 1,
.flags = IORESOURCE_MEM,
}, {
.start = INTERRUPT_I2C,
.end = INTERRUPT_I2C,
.flags = IORESOURCE_IRQ,
}
};
platform_device_register(&bcm2708_bsc0_device);

46. static u32 bcm2708_i2c_functionality(struct i2c_adapter *adap)
{
return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}
static struct i2c_algorithm bcm2708_i2c_algorithm = {
.master_xfer = bcm2708_i2c_master_xfer, // implement bus transfer function
.functionality = bcm2708_i2c_functionality,
};

47. Bus transfer function (i2c-bcm2708.c)
static int bcm2708_i2c_master_xfer( struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
struct bcm2708_i2c *bi = adap->algo_data; // chip register control
spin_lock_irqsave(&bi->lock, flags);
INIT_COMPLETION(bi->done);
bi->msg = msgs;
bi->pos = 0;
bi->nmsgs = num;
bi->error = false;
bcm2708_bsc_setup(bi); // active chip to do i2c transfer and then wait for its completion
/* unlockig _after_ the setup to avoid races with the interrupt routine */
spin_unlock_irqrestore(&bi->lock, flags);
ret = wait_for_completion_timeout(&bi->done,
msecs_to_jiffies(I2C_TIMEOUT_MS));
if (ret == 0) {
dev_err(&adap->dev, "transfer timed outn");
spin_lock_irqsave(&bi->lock, flags);
bcm2708_bsc_reset(bi);
spin_unlock_irqrestore(&bi->lock, flags);
return -ETIMEDOUT;
}
return bi->error ? -EIO : num;
}

48. I2C Adapter-Specific Code
See BCM2835 ARM
Peripherals
BSC (Broadcom Serial
Controller) p.28~p.37

49. I2C Adapter-Specific Code
See BCM2835 ARM
Peripherals
BSC (Broadcom Serial
Controller) p.28~p.37

50. cd Pi_driver/11_I2C_eerpom/bus-master
make
insmod i2c-bcm2708.ko
dmesg -c
Exercise

51. gcc eeprom-i2c.c –o eep
Lab : using LA to analyze the protocol
./eep w 0x50 0x10 0x55
./eep r 0x50 0x10

52. BCM2835 ARM Peripherals Manual
24C02C Datasheet
Kernel Documentation/ Linux I2C
Framework
References