1*4882a593Smuzhiyun===================== 2*4882a593SmuzhiyunI2C Ten-bit Addresses 3*4882a593Smuzhiyun===================== 4*4882a593Smuzhiyun 5*4882a593SmuzhiyunThe I2C protocol knows about two kinds of device addresses: normal 7 bit 6*4882a593Smuzhiyunaddresses, and an extended set of 10 bit addresses. The sets of addresses 7*4882a593Smuzhiyundo not intersect: the 7 bit address 0x10 is not the same as the 10 bit 8*4882a593Smuzhiyunaddress 0x10 (though a single device could respond to both of them). 9*4882a593SmuzhiyunTo avoid ambiguity, the user sees 10 bit addresses mapped to a different 10*4882a593Smuzhiyunaddress space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the 11*4882a593Smuzhiyun10 bit mode. This is used for creating device names in sysfs. It is also 12*4882a593Smuzhiyunneeded when instantiating 10 bit devices via the new_device file in sysfs. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunI2C messages to and from 10-bit address devices have a different format. 15*4882a593SmuzhiyunSee the I2C specification for the details. 16*4882a593Smuzhiyun 17*4882a593SmuzhiyunThe current 10 bit address support is minimal. It should work, however 18*4882a593Smuzhiyunyou can expect some problems along the way: 19*4882a593Smuzhiyun 20*4882a593Smuzhiyun* Not all bus drivers support 10-bit addresses. Some don't because the 21*4882a593Smuzhiyun hardware doesn't support them (SMBus doesn't require 10-bit address 22*4882a593Smuzhiyun support for example), some don't because nobody bothered adding the 23*4882a593Smuzhiyun code (or it's there but not working properly.) Software implementation 24*4882a593Smuzhiyun (i2c-algo-bit) is known to work. 25*4882a593Smuzhiyun* Some optional features do not support 10-bit addresses. This is the 26*4882a593Smuzhiyun case of automatic detection and instantiation of devices by their, 27*4882a593Smuzhiyun drivers, for example. 28*4882a593Smuzhiyun* Many user-space packages (for example i2c-tools) lack support for 29*4882a593Smuzhiyun 10-bit addresses. 30*4882a593Smuzhiyun 31*4882a593SmuzhiyunNote that 10-bit address devices are still pretty rare, so the limitations 32*4882a593Smuzhiyunlisted above could stay for a long time, maybe even forever if nobody 33*4882a593Smuzhiyunneeds them to be fixed. 34