VIM3 - A311D - I2C AO Clock Questions

[Neil Armstrong]

Hi,

On 06/03/2022 11:23, Lucas Tanure wrote:
> Hi,
> 
> I am trying to integrate an I2C device into VIM3 using the I2C_AO bus.
> My device uses a 100000Hz clock, but after changing
> meson-g12b-a311d-khadas-vim3.dts to add my I2C node the driver could
> not properly read its registers.
> 
> It reads 0x9100, but the correct data should be 0xcb58.
> The first thing I saw on the bus was that the frequency I requested by
> the device tree was being set after the probe of my driver already
> failed.
> For that, I sent "i2c: meson: Fix wrong speed use from probe" which
> fixes that issue.
> 
> But I still get the wrong data, so my next guess is that the clock
> duty cycle is 30%, and I think should be 50%.
> Here is an image of the signals of the bus:
> https://pasteboard.co/TEoxQucsXUUD.png
> 
> I have tested other frequencies and all of them uses a 30% duty cycle,
> where SCL is up 30% and low for 70% of the period.

Indeed it seems by default the duty cycle is for Fast Mode, but standard mode should
be around 50%. Did you try 400khz ?

Amlogic did some changes on their off-tree linux fork, please look around:
https://github.com/khadas/linux/blob/khadas-vims-5.4.y-fc/drivers/i2c/busses/i2c-meson.c#L143

I'm unsure when REG_SLAVE_ADDR BIT(28) appeared, but if you try to port this upstream,
we'll be happy to review it for inclusion.

Neil

> 
> Is possible to configure the clock to be 100000Hz, but with a 50% duty
> cycle for this I2C bus on A3111D?
> 
> Thanks
> Lucas Tanure
> 
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