im6q - undesire arm clock root frequency

[anson]

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SETTING:

PLL_ARM divider set to 16, Clock divider set to 0.

Thus, ARM clock root = 24 / 2 * 16 / ( 0 + 1)

                     = 192 Mhz

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CODE:

while(1){

     counter++;

     if (counter >= 0x40000000){     // if counter >= 1 Giga

          toggleGPIOPIN();

          resetCounter();

     }

}

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FOR 'counter++' part, 3 line assembly code is generated by the compiler:

LOAD

ADD

BRANCH

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Thus at least 3 clock cycle for the 'counter++' loop.

Time between GPIO PIN toggle should be at least  = (3 x 1 Gig) / 192 Meg

                                                 = 15.625 second

BUT the problem occur. Time between GPIO toggle is ~5 second (measure by oscilloscope)

Means the arm clock root running at least = 5 / (3 x 1Gig)

                                          = 600 Mhz

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I did try to set arm clock root to 800Mhz, but the result shows it run more then 2GHz.

WHAT IS HAPPENING??

[igorpadykov]

Hi Anson,

if you are speaking about CCM_ANALOG_PLL_ARMn

DIV_SELECT can not be 16. Valid range for divider value: 54-108.

Fout = Fin * div_select/2.0.

Sect.18.5.1.3.1 "ARM PLL" i.MX6DQ RM states:

"This PLL synthesizes a low jitter clock from a 24 MHz reference clock. The clock output

frequency for this PLL ranges from 650 MHz to 1.3 GHz. The output frequency is

selected by a 7-bit register field CCM_ANALOG_PLL_ARM[DIV_SELECT].

PLL output frequency = Fref * DIV_SEL/2"

Also it may be useful to check arm clock root

with CCM_CCOSR.

Best regards

chip

[anson]

I tried your suggestion, clkout result is not correct as well.

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ARM Clock Setting:

PLL_DIV => 54

CLK_DIV => 7

PLL_ARM                = 24 * PLL_DIV / 2

                              = 24 * 54 / 2

                              = 648 MHz

ARM CLOCK ROOT = PLL_ARM / (CLK_DIV + 1)

                              = 648 / (7 + 1)

                              =  81 MHz

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CCM_CCOSR Setting:

CCOSR_DIV => 8

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aspected clkout = ARM CLOCK ROOT / CCOSR_DIV

                        = 81 / 8

                         = 10.125 MHz

But result measure is = 5.051 MHz

[igorpadykov]

Hi Anson,

what software and board are you using ?

I would suggest to printf all registers for example

(CCM_CACRR) and its "arm_podf' value and others.

All clock generation paths one can find in Chapter 18

i.MX6DQ RM. Even better to use SDK

i.MX 6Series Platform SDK : Bare-metal SDK

Best regards

chip

[anson]

Board: Boundary Nitrogen6x with imx6q

[igorpadykov]

Hi Anson,

I would suggest to check with SDK

i.MX 6Series Platform SDK : Bare-metal SDK for the i.MX 6 series

Best regards

chip

[anson]

CCM_ANALOG_PLL_ARM      (Addr: 0x20C_8000)     Value: 0x80002036

CCM_CACRR                         (Addr: 0x20C_4010)     Value: 0x7  

CCM_CCOSR                         (Addr: 0x20C_4060)     Value: 0x01EA0001

IOMUXC_SW_MUX_CTL_PAD_GPIO03     (Addr: 0x20E_022C)     Value: 0x4

Output Measure at: clko2

OS: QNX