forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
33 lines
1.6 KiB
33 lines
1.6 KiB
===================== |
|
I2C Ten-bit Addresses |
|
===================== |
|
|
|
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.
|
|
|