topic Re: [iMX8M Plus]How to obtain precise MCLK clock ? in i.MX Processors

[iMX8M Plus]How to obtain precise MCLK clock ?

khang_letruong — Fri, 05 Aug 2022 02:58:05 GMT

Dear Community,

I am trying to configure the MCLK clock (which is input of a MIPI-CSI2 camera sensor) to achieve 37.125MHz. What I am doing is re-parenting the it as below :

clocks = <&clk IMX8MP_CLK_IPP_DO_CLKO2>; clock-names = "mclk"; assigned-clocks = <&clk IMX8MP_CLK_IPP_DO_CLKO2>; assigned-clock-parents = <&clk IMX8MP_SYS_PLL2_200M>; assigned-clock-rates = <37125000>; clock-frequency = <37125000>; mipi_csi; csi_id = <0>; mclk = <37125000>; mclk_source = <0>;

However, I only receive ~39.99MHz instead of ~37MHz :

MCLK_37MHz.jpg

Could someone tell me how to obtain the nearest value of to the expected frequency ?

Thanks in advance and best regards,
Khang

Re: [iMX8M Plus]How to obtain precise MCLK clock ?

khang_letruong — Fri, 05 Aug 2022 03:24:19 GMT

Meanwhile, for the expected 74.25Mhz, I only receive 66.66MHz as below :

clocks = <&clk IMX8MP_CLK_IPP_DO_CLKO2>; clock-names = "mclk"; assigned-clocks = <&clk IMX8MP_CLK_IPP_DO_CLKO2>; assigned-clock-parents = <&clk IMX8MP_SYS_PLL2_200M>; assigned-clock-rates = <74250000>; clock-frequency = <74250000>; mipi_csi; csi_id = <0>; mclk = <74250000>; mclk_source = <0>;

MCLK_74MHz.jpg

Regards,

Khang

Re: [iMX8M Plus]How to obtain precise MCLK clock ?

Dhruvit — Wed, 31 Aug 2022 12:26:29 GMT

Hi @khang_letruong,

I am exploring the issue, and below are the details required for further analysis to debug this issue,

Could you please measure the frequency manually with the cursor and provide me with the waveforms? This is to make sure that the measured value matches the manual measurement.
Since the 24MHz external crystal is the root clock for PLL clocks, could you please check the waveform for the 24MHz external crystal?

Thank you.
Best Regards,
Dhruvit.