Linux/AM5708: Change clock frequency of CPU and DDR

gourav roy

Part Number: AM5708

Tool/software: Linux

Hello Experts,

We have one requirement to operate CPU and DDR at 600 Mhz and 400 Mhz respectively. Found TI's wiki http://processors.wiki.ti.com/index.php/Linux_Porting_Guide_for_AM571x/AM570x_Speed_Grades

In the above wiki for 500 Mhz structure is mentioned like

static const struct dpll_params mpu_dpll_params_500mhz[NUM_SYS_CLKS] = {
        {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},       /* 12 MHz   */
        {200, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},       /* 20 MHz   */
        {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},       /* 16.8 MHz */
        {365, 13, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},      /* 19.2 MHz */
        {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},       /* 26 MHz   */
        {500, 26, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},      /* 27 MHz   */
        {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1},       /* 38.4 MHz */
};

Could you please let me know what is logic for the above structure and how to create structure for 600 Mhz.

Thanks,
Gourav

over 5 years ago

0 Pavel Botev over 5 years ago

TI__Guru**** 170625 points

Hi Roy,

It depends on what is your main crystal frequency. On AM572x TI EVM we have 20MHz main clock source, thus for 1GHz we have:

/* OPP NOM FREQUENCY for OMAP5 ES2.0, and DRA7 ES1.0 */

static const struct dpll_params mpu_dpll_params_1ghz[NUM_SYS_CLKS] = {

{250, 2, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 12 MHz */

{500, 9, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 20 MHz */

{119, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 16.8 MHz */

{625, 11, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 19.2 MHz */

{500, 12, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 26 MHz */

{-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 27 MHz */

{625, 23, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 38.4 MHz */

};

This line means we have M=500, N=9, M2=1, the rest of the parameters (M3, M4, M4, M7, H21, H22, H23, H24) are not applicable, thus filled with -1.

The formulas are:

Fdpll = Fref x 2 x M / (N+1) = 20 x 2 x 500 / (9 + 1) = 2000

CLKOUT_M2 = Fdpll / (2 x M2) = 2000 / (2 x 1) = 1000 = 1GHz

gourav roy said:
static const struct dpll_params mpu_dpll_params_500mhz[NUM_SYS_CLKS] = { {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 12 MHz */ {200, 7, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 20 MHz */

Here we have:

Fdpll = Fref x 2 x M / (N+1) = 20 x 2 x 200 / (7 + 1) = 1000

CLKOUT_M2 = Fdpll / (2 x M2) = 1000 / (2 x 1) = 500MHz

So for 600MHz with 20MHz crystal you can use the below line:

{300, 9, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 20 MHz */

{240, 7, 1, 1, -1, -1, -1, -1, -1, -1, -1, -1}, /* 20 MHz */

For more info check below TRM sections:

3.6.3.3.2 DPLLs Output Clocks Parameters

3.6.3.7 DPLL_MPU Description

And below u-boot files:

u-boot/arch/arm/mach-omap2/omap5/hw_data.c

u-boot/arch/arm/mach-omap2/clocks-common.c

u-boot/arch/arm/include/asm/omap_common.h

Check also below e2e threads:

https://e2e.ti.com/support/legacy_forums/omap/f/885/t/338011

Regards,
Pavel

0 gourav roy over 5 years ago in reply to Pavel Botev

Intellectual 840 points

Thanks a lot Pavel.

To change DDR clock frequency to 400 Mhz can i use same formula? and which structure do we need to change for ddr frequency?

Thanks,
Gourav

0 Pavel Botev over 5 years ago in reply to gourav roy

TI__Guru**** 170625 points

Gourav,

Yes, the same formula. You can use M=200

For AM5708 device, I think ddr_dpll_params_2664mhz should be changed.

Regards,
Pavel

0 gourav roy over 5 years ago in reply to Pavel Botev

Intellectual 840 points

Thanks Pavel,

Could you please let me know, how to verify clock frequency of DDR once board boot up.

We can verity cpu frequency on running board by

root@am57xx-evm:/sys/devices/system/cpu/cpu0/cpufreq# cat cpuinfo_cur_freq

In similar manner is there any procedure to get DDR clock on board?

Thanks,

Gourav

0 Pavel Botev over 5 years ago in reply to gourav roy

TI__Guru**** 170625 points

Gourav,

You can use omapconf tool.

root@am57xx-evm:~# omapconf --help
root@am57xx-evm:~# omapconf show dpll
root@am57xx-evm:~# omapconf show opp

On my side (AM572x EVM), for DPLL_DDR, it reports:

Lock Frequency (MHz): 2128
Clock Speed (MHz): 532

For AM5708 device, you should use omapconf tool with "--force dra72x" option.

Regards,
Pavel

0 gourav roy over 5 years ago in reply to Pavel Botev

Intellectual 840 points

Thanks a lot for your support Pavel.

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Linux/AM5708: Change clock frequency of CPU and DDR