| 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. |
