Determining T1042 timebase frequency

[nakrachi]

Hi Everyone,

We are trying to determine the right frequency at which the timebase is updated. 

According to the reference manual the core timebase frequency is calculated as follows :

Timebase clock = (platform_clock/16) / TBCLKDIVR

in our case :

• Platform clock is 600 Mhz
• RCPM_PCTBCKSELR is 0 -> Core Timebase is clocked with Platform Clock /16
• TBCLKDIVR is 0x2 -> 1/8 

so our timebase frequency should be : 600/(16*8) = 4.6875 Mhz 

but when measuring with the logic analyzer we get a timebase frequency of 50Mhz.

I would like to confirm if I a calculated the right frequency or if I missed something, 

thank you 

[nakrachi]

The only pin available to me was the UART_SOUT which I had to configure as GPIO1[15] by modifying the RCW. 

I used the debugger RCW override function to use my new RCW, I figured out that the debugger will set the platform PLL to 4:1 even though my RCW is setting it to be 6:1. meaning that my platform clock is 400 Mhz and not 600 Mhz (SYSCLK is 100Mhz). 

which make a little bit more sense, if we consider that platform clock is only divided by TBCLKDIVR, 400Mhz/8 = 50 Mhz

 I think that "RCPM_PCTBCKSELR is 0 -> Core Timebase is clocked with Platform Clock /16" statement is not true. 

Can you please confirm.

thank you

[ufedor]

You wrote:

> when measuring with the logic analyzer we get a timebase frequency of 50Mhz

How exactly you did that?

[nakrachi]

Thanks for the reply,

I did set the decrementer to a value of 50000 ticks 

with Auto reload enabled (TCR= 0x0000000000400000) 

then in the decrementer exception vector (IVOR10) I toggle a GPIO which I measure with the logic analyzer. 

I get a frequency of 1Khz (a period of 1 ms) 

which makes me believe I am running at 50 Mhz (50000 * 1Khz) 

[ufedor]

DECAR in your case is zero.

[nakrachi]

The debugger can't read it (according to core manual "The DECAR contents cannot be read") 

but I know that I wrote the right value and I am getting decremented exceptions at a fixed interval. 

[ufedor]

Please show using Trace32 values of:

RCPM_PCTBCKSELR

RCPM_TBCLKDIVR

[nakrachi]

Here is a screenshot

[ufedor]

What is SYSCLK frequency?

Please provide U-Boot booting log.

[nakrachi]

The system frequency is 100MHz 

here is the u-boot log 

[ufedor]

600/50=12

I have no idea how such ratio can be obtained.

[ufedor]

Please combine all consistent experimental data into single Word or PDF document.

[nakrachi]

just making sure, you want me to describe the issue with relevant data/screenshots and post it here ?

thanks

[ufedor]

Yes, please.

[nakrachi]

@ufedor please fin attached the requested document. 

Thanks

[nakrachi]

Hi @ufedor , just following up on this.

thanks

[ufedor]

Your understanding is correct.

Time base frequency = (Platform clock )/RCPM_TBCLKDIVR When RCPM_PCTBCKSELR [PCTBCKSELn] = 0, Core Timebase is clocked with Platform Clock/ RCPM_TBCLKDIVR [tbclkdiv].

It is recommended to have the default value of RCPM_TBCLKDIVR [tbclkdiv], i.e., 0x00 : 1/16. This field should not be modified by customer as all the testing are done with Timebase clock divider configuration = 1/16.

Comment is added in T1042RM.

[nakrachi]

Thank you,

But then we have another problem, the erratum A-010651 states that the workaround is changing the RCPM_TBCLKDIVR [tbclkdiv], to 0x08 : 1/32.

but you mentioned we should not change it. how can we workaround this errata then ?

thanks

[nakrachi]

Thanks for the quick replies,

as I mentioned in an earlier comment, I found out that using the temporary RCW has set my PLL ration to 4:1 so I was running at 400Mhz when I got 50Mhz. 

Now after setting back the platform clock to 600Mhz  I measure a time base frequency of 75Mhz. (600/8)

which makes me believe that the user manual is wrong