I2C speed - change

Technical Support
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1

Hey,

I saw on an oscilloscope that, when calling e.g. i2cget on i2c-0, that the speed is 400kHz.
I need it at 100kHz.

Then I found this forum thread:
NVIDIA forum

The last post says that you just need to do this to alter the speed at runtime for testing:

echo 10000 > /sys/bus/i2c/devices/i2c-<BUS>/bus_clk_rate

The file “bus_clk_rate” does not exist under any of the i2c devices, though.
Is the NVIDIA code base used for your L4T image older than what the forum poster refers to?

How else would I change the I²C speed?

EDIT: btw, i2cdetect, on i2c-0, lists one address as “UU”, which apparently means the system is using that. Is there something conncted already for which a driver is being used? On the ixora board, or the module?

EDIT #2: Apart from the nice run-time experimental “echo to file” method linked above, which does not work with the L4T image, it seems modifying the device tree is the only way?
So I decompiled, modified, recompiled the /boot/tegra124-jetson_tk1-pm375-000-c00-00.dtb, stored it in /boot/ under another file name, and added another LABEL to /boot/extlinux/jetson-tk1_extlinux.conf.emmc, to get a boot option to start using the modified dtb on demand.
I am not presented with a boot option on the serial console, though.
Any ideas why not?

2

Hi @sktpin

Could you provide the version of the hardware (including carrier board) and software ( uname -a ) of your module?

Best regards,
Jaski

3

I added it

4

Oh! I just saw it reads a different .dtb file than is stated in the …_extlinux.conf.emmc:
Booting from internal eMMC chip…
reading tegra124-apalis-v1.2-eval.dtb

Was what I saw on the seria. console. No idea where that file is residing. So that exlinux.conf… is apparently the wrong config file, but, the others in that folder have suffixes that sound much less appropriate, so I guess… on tha tinstallation, that folder is somehow “dead” but still present for whatever reason, and the real action is elsewhere?

5

Thanks for this.

6

can you tell where this comes from? (see my older comment below, which somehow did not end up in this branch)

7

I think you deleted a comment. If a parent comment is deleted then the child comment is also deleted.

Could you explain again, what is your issue?