topic Re: Vybrid core clock setting in Vybrid Processors

Vybrid core clock setting

jeremyesquirol — Thu, 21 Nov 2013 15:56:03 GMT

Hi !

I'm using a TWR-VF6xx with Embedded Linux on cortex-A5 core. It seems that the core clock is set to 396Mhz using PLL1_PFD3 (register value read with DS-5).

First, I don't understand where the core clock is initialized ? I've seen in file clock.c that all clocks are registered but the function :

int  __init mvf_clocks_init(unsigned long ckil, unsigned long osc, unsigned long ckih1, unsigned long ckih2)
[...]
// keep correct count
    cpu_clk.usecount++;
    pll1_sys_main_clk.usecount += 5;
    pll2_528_bus_main_clk.usecount += 5;
    periph_clk.usecount++;
    ipg_clk.usecount++;

#if 0
    clk_set_parent(&periph_clk, &pll2_pfd2_396M);
    clk_enable(&periph_clk); /* platform bus clk */
    clk_enable(&ipg_clk); /* ips bus clk */
#endif
    clk_enable(&pll3_usb_otg_main_clk);

only enable pll3_usb_otg_main_clock ? Where are enabled the others?

Second, there are some vybrid specific function in this file, and my goal is just to set the core clock to 450Mhz. I just modify the .parent of the PLL1_SW_CLK by PLL1_PFD2_450M using the function

static int _clk_pll1_sw_set_parent(struct clk *clk, struct clk *parent)

but it seems that has no effect. Is anyone can help me?

Re: Vybrid core clock setting

billpringlemeir — Thu, 21 Nov 2013 21:17:26 GMT

Some clocks are assumed to be initialized by the boot loader (u-boot). U-boot must also initialize many of these clocks to work with the 'fec' and to load your Linux kernel.

If you are restarting the core clock, you may need to re-initialize some things and probably can not have SDRAM, etc running as those clock modules will be derived from the main PLL; at least this is the case with other Freescale CPUs. You are probably better off looking at the u-boot source, if you don't want to do this dynamically. The source is at Timesys/u-boot-timesys · GitHub.

Re: Vybrid core clock setting

jeremyesquirol — Mon, 25 Nov 2013 11:22:51 GMT

Thank you Bill, you solve my problem.

The clock is initialised in lowlevel_init.S file in u-boot source.