1*ccf988b6SMauro Carvalho Chehab===================== 2*ccf988b6SMauro Carvalho ChehabI2C Ten-bit Addresses 3*ccf988b6SMauro Carvalho Chehab===================== 4*ccf988b6SMauro Carvalho Chehab 5*ccf988b6SMauro Carvalho ChehabThe I2C protocol knows about two kinds of device addresses: normal 7 bit 6*ccf988b6SMauro Carvalho Chehabaddresses, and an extended set of 10 bit addresses. The sets of addresses 7*ccf988b6SMauro Carvalho Chehabdo not intersect: the 7 bit address 0x10 is not the same as the 10 bit 8*ccf988b6SMauro Carvalho Chehabaddress 0x10 (though a single device could respond to both of them). 9*ccf988b6SMauro Carvalho ChehabTo avoid ambiguity, the user sees 10 bit addresses mapped to a different 10*ccf988b6SMauro Carvalho Chehabaddress space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the 11*ccf988b6SMauro Carvalho Chehab10 bit mode. This is used for creating device names in sysfs. It is also 12*ccf988b6SMauro Carvalho Chehabneeded when instantiating 10 bit devices via the new_device file in sysfs. 13*ccf988b6SMauro Carvalho Chehab 14*ccf988b6SMauro Carvalho ChehabI2C messages to and from 10-bit address devices have a different format. 15*ccf988b6SMauro Carvalho ChehabSee the I2C specification for the details. 16*ccf988b6SMauro Carvalho Chehab 17*ccf988b6SMauro Carvalho ChehabThe current 10 bit address support is minimal. It should work, however 18*ccf988b6SMauro Carvalho Chehabyou can expect some problems along the way: 19*ccf988b6SMauro Carvalho Chehab 20*ccf988b6SMauro Carvalho Chehab* Not all bus drivers support 10-bit addresses. Some don't because the 21*ccf988b6SMauro Carvalho Chehab hardware doesn't support them (SMBus doesn't require 10-bit address 22*ccf988b6SMauro Carvalho Chehab support for example), some don't because nobody bothered adding the 23*ccf988b6SMauro Carvalho Chehab code (or it's there but not working properly.) Software implementation 24*ccf988b6SMauro Carvalho Chehab (i2c-algo-bit) is known to work. 25*ccf988b6SMauro Carvalho Chehab* Some optional features do not support 10-bit addresses. This is the 26*ccf988b6SMauro Carvalho Chehab case of automatic detection and instantiation of devices by their, 27*ccf988b6SMauro Carvalho Chehab drivers, for example. 28*ccf988b6SMauro Carvalho Chehab* Many user-space packages (for example i2c-tools) lack support for 29*ccf988b6SMauro Carvalho Chehab 10-bit addresses. 30*ccf988b6SMauro Carvalho Chehab 31*ccf988b6SMauro Carvalho ChehabNote that 10-bit address devices are still pretty rare, so the limitations 32*ccf988b6SMauro Carvalho Chehablisted above could stay for a long time, maybe even forever if nobody 33*ccf988b6SMauro Carvalho Chehabneeds them to be fixed. 34