Spread spectrum modulation of i.MX6UL

[yuuki]

Dear all,

We want to enable the Spread spectrum modulation for DCLK of the LCD.

We observed a waveform by using spectrum analyzer.

LDB_DI0_CLK_SEL=PLL2 PFD3

CCM_CS2CDR: 0x020C402C = 0x0055B6EF

【SSCG-ON】Spread spectrum modulation enabled

CCM_ANALOG_PLL_SYSn: 0x020C8030 = 0x80002001

CCM_ANALOG_PLL_SYS_SS: 0x020C8040 = 0x05DC8006

CCM_ANALOG_PLL_SYS_DENOM: 0x020C8060 = 0x00000012

【SSCG-ON + DENOM setting】Spread spectrum modulation enabled + Denominator setting

CCM_ANALOG_PLL_SYSn: 0x020C8030 = 0x80002001

CCM_ANALOG_PLL_SYS_SS: 0x020C8040 = 0x05DC8006

CCM_ANALOG_PLL_SYS_DENOM: 0x020C8060 = 0x00001770

【SSCG-OFF】Spread spectrum modulation disabled

CCM_ANALOG_PLL_SYSn: 0x020C8030 = 0x80002001

CCM_ANALOG_PLL_SYS_SS: 0x020C8040 = 0x05DC0006

CCM_ANALOG_PLL_SYS_DENOM: 0x020C8060 = 0x00000012

We suspect that setting is not enough

Is there a more necessary setting?

These setting is set by the imx6ul_clocks_init() function in the clk-imx6ul.c file of Yocto Linux BSP.

Should these registers be set in U-Boot too?

May I have advice?

Best Regards,

Yuuki

[art · Accepted solution]

Your Case #2 should work well producing the frequency deviation range of 6MHz and frequency modulation rate of 24kHz. Please note that you first have to set up the CCM_ANALOG_PLL_SYS_DENOM register and STOP and STEP fields of the CCM_ANALOG_PLL_SYS_SS register and only after that set the CCM_ANALOG_PLL_SYS_SS[ENABLE] bit. With other sequence, the spread spectrum function may not start properly.

Have a great day,
Artur

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[yuuki]

Dear Artur-san,

Thank you for your support.

I'm sorry, we found it having got a wrong setting

We set PLL3 as a clock source for the LDB module.

I was able to confirm Spread spectrum by setting PLL2.

Best Regards,

Yuuki