TM4C1294NCPDT: SysCtlClockGet() is giving me 1017.xx M value

Hi Tayyab,

 For TM4C129 device please use the returned value from SysctlClockFreqSet() to obtain the processor clock rate instead of calling SysCtlClockGet(). The SysCtlClockGet() can only be called on TM4C123 devices. This is mentioned in the TivaWare library.

26.2.2.3 SysCtlClockGet
Gets the processor clock rate.
Prototype:
uint32_t
SysCtlClockGet(void)
Description:
This function determines the clock rate of the processor clock, which is also the clock rate
of the peripheral modules (with the exception of PWM, which has its own clock divider; other
peripherals may have different clocking, see the device data sheet for details).

Note:
This cannot return accurate results if SysCtlClockSet() has not been called to configure the
clocking of the device, or if the device is directly clocked from a crystal (or a clock source)
that is not one of the supported crystal frequencies. In the latter case, this function should be
modified to directly return the correct system clock rate.
This function can only be called on TM4C123 devices. For TM4C129 devices, the return value
from SysCtlClockFreqSet() indicates the system clock frequency.

Tayyab Tahir said:

here  g_ui32SysClock gives the right value that is 12 Mega

but i want to confirm either the clock is accurate or not.

Based upon your (earlier) code entry: "...| SYSCTL_CFG_VCO_480), 120000000);"  should not that SysClock be 120MHz - NOT 12MHz?

You also seek to confirm the accuracy of the System Clock.    Yet - you do not specify, "How that accuracy is to be measured & determined?"  That's of (some) importance - is it not?

Consider the following:

• you seek to "confirm SysClock accuracy" using (only) your MCU.      If that (MCU alone) is your "only means of measurement" - how then do you propose to achieve measurement accuracy?
• to overcome that shortfall - you must provide a, "sufficiently accurate" external frequency source;" or you may output a replica of SysClock - and using external equipment - measure that.    (i.e. that was friend/vendor David's suggestion)

While your post is "unclear" as to which of those 2 methods you seek - my sense was you "expected" the MCU (alone) "to confirm SysClock's accuracy" - which of course - minus any "on-chip" frequency standard - it cannot achieve!

Should you seek to design a product which enables such, "Reasonably Accurate Measure of SysClock" - your provision of an adequately accurate, external, stable (voltage, age, temperature)  frequency source must be deployed (properly) upon your MCU's pcb.

Note too that "everyone's" understanding & acceptance of  "accurate" - may NOT fully overlap your own.      Thus (some) specification IS required - is that not so?

thanks for your response 

I am sorry its 120 M not 12 M.

Also let me put it in that way 

i want to sample the system clock on a scope or logic analyzer to check whether it is the requested clock that i mentioned in SysClockFreqSet(.......,120000000).

if the clock could be sample on a GPIO it would be best (if possible)

A friend of mine said that may be a PWM may help i have gone through TIVA ware documentation on search of anything related 

could you please sample a code to do so 

or else point me in the direction so that i can do so 

Thanks