Commit | Line | Data |
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89140f41 | 1 | The I2C protocol knows about two kinds of device addresses: normal 7 bit |
1da177e4 LT |
2 | addresses, and an extended set of 10 bit addresses. The sets of addresses |
3 | do not intersect: the 7 bit address 0x10 is not the same as the 10 bit | |
cbb44514 | 4 | address 0x10 (though a single device could respond to both of them). |
cfa0327b WS |
5 | To avoid ambiguity, the user sees 10 bit addresses mapped to a different |
6 | address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the | |
7 | 10 bit mode. This is used for creating device names in sysfs. It is also | |
8 | needed when instantiating 10 bit devices via the new_device file in sysfs. | |
1da177e4 | 9 | |
cbb44514 JD |
10 | I2C messages to and from 10-bit address devices have a different format. |
11 | See the I2C specification for the details. | |
1da177e4 | 12 | |
cbb44514 JD |
13 | The current 10 bit address support is minimal. It should work, however |
14 | you 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 | ||
26 | Note that 10-bit address devices are still pretty rare, so the limitations | |
27 | listed above could stay for a long time, maybe even forever if nobody | |
28 | needs them to be fixed. |