1=====================
2I2C Ten-bit Addresses
3=====================
4
5The I2C protocol knows about two kinds of device addresses: normal 7 bit
6addresses, and an extended set of 10 bit addresses. The sets of addresses
7do not intersect: the 7 bit address 0x10 is not the same as the 10 bit
8address 0x10 (though a single device could respond to both of them).
9To avoid ambiguity, the user sees 10 bit addresses mapped to a different
10address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the
1110 bit mode. This is used for creating device names in sysfs. It is also
12needed when instantiating 10 bit devices via the new_device file in sysfs.
13
14I2C messages to and from 10-bit address devices have a different format.
15See the I2C specification for the details.
16
17The current 10 bit address support is minimal. It should work, however
18you can expect some problems along the way:
19
20* Not all bus drivers support 10-bit addresses. Some don't because the
21  hardware doesn't support them (SMBus doesn't require 10-bit address
22  support for example), some don't because nobody bothered adding the
23  code (or it's there but not working properly.) Software implementation
24  (i2c-algo-bit) is known to work.
25* Some optional features do not support 10-bit addresses. This is the
26  case of automatic detection and instantiation of devices by their,
27  drivers, for example.
28* Many user-space packages (for example i2c-tools) lack support for
29  10-bit addresses.
30
31Note that 10-bit address devices are still pretty rare, so the limitations
32listed above could stay for a long time, maybe even forever if nobody
33needs them to be fixed.
34