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coreboot-libre-fam15h-rdimm/3rdparty/chromeec/docs/i2c-debugging.md

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I²C Debugging Tips

The EC codebase has functionality to help you debug I²C errors without pulling out the scope. Some of the debug functionality is disabled by default to save space, but can be enabled with the CONFIG_I2C_DEBUG option.

Tracing

You can use the i2ctrace command to monitor (ranges of) addresses:

i2ctrace [list
        | disable <id>
        | enable <port> <address>
        | enable <port> <address-low> <address-high>]

For example:

> i2ctrace enable 0 0x10 0x30
> i2ctrace enable 0 0x40 0x50
> i2ctrace list
id port address
-- ---- -------
0     0 0x10 to 0x30
1     0 0x40 to 0x50
... debug spam may follow ...
i2c: write 0:0x50 A8
i2c: read 0:0x50 00 02 00 06 00 44
...
> i2ctrace disable 1
> i2ctrace list
id port address
-- ---- -------
0     0 0x10 to 0x30

A maximum of 8 debug entries are supported at a single time.

Note that i2ctrace enable will merge debug entries when possible:

> i2ctrace enable 0 0x10 0x30
> i2ctrace enable 0 0x40 0x50
> i2ctrace enable 0 0x31 0x3f
> i2ctrace list
id port address
-- ---- -------
0     0 0x10 to 0x50