I can´t undertand SysCtlClockGet() behaviour

[Simao 0]

     Hi there, I would really appreciate any  help here. Assuming ClockVal defined as

 

unsigned long Clockval=0

     After executing this 2 lines of code...    
     

SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);
 
ClockVal = SysCtlClockGet();

     What should be the correct value of Clockval? A friend of mine reported 40,000.000  meaning 40 Mhz using IAR, in my case running Keil I get 3,200000 or 3.2 Mhz, does abybody have a clue for this weird value??

Thanks a lot in advance

 

Simao

 

 

P.S.  1) We both use Stellaris LM4F120 LaunchPad Evaluation Kit

 

P.S.  2) It´s my first post so please bear with me if it´s not formaly correct.

[bluehash 1,577]

@@Simao

 

Following will set the Stellaris Launchpad at 80Mhz

SysCtlClockSet(	SYSCTL_SYSDIV_2_5 | SYSCTL_USE_PLL |	\
					SYSCTL_OSC_MAIN   | SYSCTL_XTAL_16MHZ);

What this means is - You are instructing the PLL to run to 400Mhz using the 16Mhz as input to it. The PLL is then divided by 2 internally in hardware, and then 2.5

400/2/2.5 = 80

SysCtlClockGet() will give you 80000000Hz.

SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);
 
ClockVal = SysCtlClockGet();

400/2/5 = 40Mhz

 

Explained here too.

[Simao 0]

     Thanks a lot for your explanation. I´ll try your tip for 80Mhz and I`ll keep you informed.

 

 

Simão

[bluehash 1,577]

     Thanks a lot for your explanation. I´ll try your tip for 80Mhz and I`ll keep you informed.

 

 

Simão

It is kind of confusing, but look up the clock diagram in the datasheet. What plans do you have for it?

[Simao 0]

     Acctually it worked already, my concern is about the value I get when I call SysCtlClockGet(), I guess I have to dig into KEIL help files to know what is happening but freq is OK.

     Thanks again.

 

Simao