1The I2C protocol knows about two kinds of device addresses: normal 7 bit 2addresses, and an extended set of 10 bit addresses. The sets of addresses 3do not intersect: the 7 bit address 0x10 is not the same as the 10 bit 4address 0x10 (though a single device could respond to both of them). 5To avoid ambiguity, the user sees 10 bit addresses mapped to a different 6address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the 710 bit mode. This is used for creating device names in sysfs. It is also 8needed when instantiating 10 bit devices via the new_device file in sysfs. 9 10I2C messages to and from 10-bit address devices have a different format. 11See the I2C specification for the details. 12 13The current 10 bit address support is minimal. It should work, however 14you can expect some problems along the way: 15* Not all bus drivers support 10-bit addresses. Some don't because the 16 hardware doesn't support them (SMBus doesn't require 10-bit address 17 support for example), some don't because nobody bothered adding the 18 code (or it's there but not working properly.) Software implementation 19 (i2c-algo-bit) is known to work. 20* Some optional features do not support 10-bit addresses. This is the 21 case of automatic detection and instantiation of devices by their, 22 drivers, for example. 23* Many user-space packages (for example i2c-tools) lack support for 24 10-bit addresses. 25 26Note that 10-bit address devices are still pretty rare, so the limitations 27listed above could stay for a long time, maybe even forever if nobody 28needs them to be fixed. 29
