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