在uboot下输入i2c命令后，会返回以下信息。
其中的i2c dev/i2c probe/i2c speed较容易理解和使用。
但i2c md等命令说明不是常规的写法，解读起来有些困难。
uboot>i2c
i2c - I2C sub-system
Usage:
i2c crc32 chip address[.0, .1, .2] count - compute CRC32 checksum
i2c dev [dev] - show or set current I2C bus
i2c loop chip address[.0, .1, .2] [# of objects] - looping read of device
i2c md chip address[.0, .1, .2] [# of objects] - read from I2C device
i2c mm chip address[.0, .1, .2] - write to I2C device (auto-incrementing)
i2c mw chip address[.0, .1, .2] value [count] - write to I2C device (fill)
i2c nm chip address[.0, .1, .2] - write to I2C device (constant address)
i2c probe [address] - test for and show device(s) on the I2C bus
i2c read chip address[.0, .1, .2] length memaddress - read to memory
i2c write memaddress chip address[.0, .1, .2] length - write memory to i2c
i2c reset - re-init the I2C Controller
i2c speed [speed] - show or set I2C bus speed
在uboot的源代码cmd/i2c.c中有详细解释说明
i2c md chip address[.0, .1, .2] [# of objects] - read from I2C device
以执行命令i2c md 0x50 0.2 0x40为例子，从slave地址0x50(7位地址)，从i2c设备的0x0开始（2个字节），读取0x40个字节
1: 0x50对应chip，是i2c的slave地址。
2: 0.2 对应address[.0, .1, .2]，指两个字节的地址位，对应地址0x0000
3: 0x40为读取的数目，为16进制。
以执行命令i2c md 0x50 0x0f80.2 0x40为例子，从slave地址0x50(7位地址)，从i2c设备的0x0f80开始（2个字节），读取0x40个字节
/*
* I2C Functions similar to the standard memory functions.
*
* There are several parameters in many of the commands that bear further
* explanations:
*
* {i2c_chip} is the I2C chip address (the first byte sent on the bus).
* Each I2C chip on the bus has a unique address. On the I2C data bus,
* the address is the upper seven bits and the LSB is the "read/write"
* bit. Note that the {i2c_chip} address specified on the command
* line is not shifted up: e.g. a typical EEPROM memory chip may have
* an I2C address of 0x50, but the data put on the bus will be 0xA0
* for write and 0xA1 for read. This "non shifted" address notation
* matches at least half of the data sheets :-/.
*
* {addr} is the address (or offset) within the chip. Small memory
* chips have 8 bit addresses. Large memory chips have 16 bit
* addresses. Other memory chips have 9, 10, or 11 bit addresses.
* Many non-memory chips have multiple registers and {addr} is used
* as the register index. Some non-memory chips have only one register
* and therefore don't need any {addr} parameter.
*
* The default {addr} parameter is one byte (.1) which works well for
* memories and registers with 8 bits of address space.
*
* You can specify the length of the {addr} field with the optional .0,
* .1, or .2 modifier (similar to the .b, .w, .l modifier). If you are
* manipulating a single register device which doesn't use an address
* field, use "0.0" for the address and the ".0" length field will
* suppress the address in the I2C data stream. This also works for
* successive reads using the I2C auto-incrementing memory pointer.
*
* If you are manipulating a large memory with 2-byte addresses, use
* the .2 address modifier, e.g. 210.2 addresses location 528 (decimal).
*
* Then there are the unfortunate memory chips that spill the most
* significant 1, 2, or 3 bits of address into the chip address byte.
* This effectively makes one chip (logically) look like 2, 4, or
* 8 chips. This is handled (awkwardly) by #defining
* CONFIG_SYS_I2C_EEPROM_ADDR_OVERFLOW and using the .1 modifier on the
* {addr} field (since .1 is the default, it doesn't actually have to
* be specified). Examples: given a memory chip at I2C chip address
* 0x50, the following would happen...
* i2c md 50 0 10 display 16 bytes starting at 0x000
* On the bus: A0 00 A1 ...
* i2c md 50 100 10 display 16 bytes starting at 0x100
* On the bus: A2 00 A3 ...
* i2c md 50 210 10 display 16 bytes starting at 0x210
* On the bus: A4 10 A5 ...
* This is awfully ugly. It would be nice if someone would think up
* a better way of handling this.
*
* Adapted from cmd_mem.c which is copyright Wolfgang Denk (wd@denx.de).
*/
参考执行示例
uboot>i2c dev
Current bus is 9
uboot>i2c dev 6
Setting bus to 6
uboot>i2c dev
Current bus is 6
uboot>i2c dev 9
Setting bus to 9
uboot>i2c md 0x50 0.2 0x40
0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
0010: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
0020: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
0030: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
uboot>
uboot>i2c probe 0x50
Valid chip addresses: 50
uboot>i2c probe 0xa0
Valid chip addresses:
uboot>i2c speed
Current bus speed=100000
uboot i2c
