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