OMAPL138 PLL Initializaiton Procedure

Hi,

We are working on this request and will get back to you at the earliest.

Thanks & regards,
Sivaraj K

Hi Yasunori,

In EVMOMAPL138_ARM.gel file, the code for stabilization is generic for the three PLL sequence mentioned in the OMAPl138 TRM.

Actually, after power up and the frequency lock sequence of PLL is complete, the PLL will be ready for any configuration modes ( i.e. PLLM or bypass mode ). 

1. Consider if the PLL0 is already intialized and configured in bypass mode, then the code below for stabilization is not required. But if the PLL0 is already in PLLM mode, then it might be required for transition and stabilization. And more over, for your project requirement, if the change sequence of PLL is wellknown and fixed ,then you can either remove or modify by reducing the stabilisation time.

/*PLL stabilisation time- take out this step , not required here when PLL in bypassmode*/

  for(i=0; i<PLL_STABILIZATION_TIME; i++) {;}

When we compared to the gel file of OMAPL137, as it has only one function, Setup_PLL(), this stabilization waitcycles code is commented out. There is no separate functions like Set_Core_456MHz(), Set_Core_300MHz().

 

 

 

 

Hi Shankari,

Thank you for your reply.
I understand that "stabilization time" is not required if PLL is already configured in bypass mode.

I have additional questions. Please tell me the following.

1 .
The three PLL sequence, I think the following three.
OMAP-L138 TRM (spruh77a.pdf)
- 8.2.2.2 Initializing PLL Mode from PLL Power Down
- 8.2.2.3 Changing PLL Multiplier
- 8.2.2.4 Changing SYSCLK Dividers

"8.2.2.2" and "8.2.2.3", I think "stabilization time" is not required because they contains "Switch the PLL to bypass mode" (PLL is configured in bypass mode).
"8.2.2.4" does not contain "Switch the PLL to bypass mode", but, "stabilization time" is not included in the corresponding part in device_PLL0().
---------------------------------------------
/*Check for the GOSTAT bit in PLLSTAT to clear to 0 to indicate that no GO operation is currently in progress*/
while(PLL0_PLLSTAT & 0x1==1){}

/*Program the RATIO field in PLLDIVx with the desired divide factors. In addition, make sure in this step you leave the PLLDIVx.DxEN bits set so clocks are still enabled (default).*/
PLL0_PLLDIV1 = 0x8000 | PLLDIV1; /* Make PLLDIV1 as bootpacket, do it for other PLLDIVx to if required*/
PLL0_PLLDIV2 = 0x8000 | PLLDIV2;
PLL0_PLLDIV4 = 0x8000 | (((PLLDIV1+1)*4)-1);
PLL0_PLLDIV6 = 0x8000 | PLLDIV1;
PLL0_PLLDIV3 = 0x8000 | PLLDIV3; /* Make PLLDIV3 as bootpacket, do it for other PLLDIVx to if required*/
PLL0_PLLDIV7 = 0x8000 | PLLDIV7; /* Make PLLDIV7 as bootpacket, do it for other PLLDIVx to if required*/


/*Set the GOSET bit in PLLCMD to 1 to initiate a new divider transition.*/
PLL0_PLLCMD |= 0x1;

/*Wait for the GOSTAT bit in PLLSTAT to clear to 0 (completion of phase alignment).*/
while(PLL0_PLLSTAT & 0x1==1) { }
---------------------------------------------

Also, in clock.c contained in the OMAPL138 PSP (linux-xxxx/arch/arm/mach-davinci/clock.c), it does not found.
- davinci_set_pllrate(): for "8.2.2.3 Changing PLL Multiplier"
- davinci_set_sysclk_rate(): for "8.2.2.4 Changing SYSCLK Dividers"
In either case, "stabilization time" does not found.

so, I think "stabilization time" is not required in the three(all) PLL sequence.
Is this correct ?

2.
If there is a case that "stabilization time" is required,
what kind of case is it ?
how long time is needed ?

Best Regards,
Yasunori

Hi Shankari,

Thank you for your reply.
I understood that "stabilization time" is not required in the three PLL sequence.

> For example:- From Set_Core_300MHz to Set_Core_456MHz().

Both Set_Core_300MHz() and Set_Core_456MHz() calls device_PLL0().
In device_PLL0(), PLL is put in bypass mode. (before to program)
Therefore, I think that "stabilization time" is not required in this case.

Best Regards,
Yasunori

Hi Yasunori,

Superb job.

Thanks for your effort in confirming this. This information will be useful for the community members.
On your post above, please click on verify answer button.

In the next release ( if any ) , I would like to bring your observation to the internal team to remove the stabilization code in the gel file.

Thanks.