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Spread spectrum modulation of i.MX6UL

Question asked by yuuki on Jul 4, 2016
Latest reply on Jul 10, 2016 by 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

01_SSCG-ON.png

 

【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

02_SSCG-ON+DENOMsetting.png

 

【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

03_SSCG-OFF.png

 

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

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