getting 2 sec delay by using SysCtlDelay(SysCtlClockGet()/3)

Hi Swati,

     I tried that using a Stellaris Evaluation kit and I got a 1 second interval. How are you setting your SysCtlClockSet()?Post your code here for review.

-kel

Depending upon the MCU System Clock speed - MCU revision - and your code's location (i.e. flash vs. SRAM) that function (SysCtlDelay) may not supply highest accuracy.

As factory here (i.e. Dave W.)  has several times advised - best "time accuracy" is consistently achieved via use of one of the Timers - supplied in abundance - by ARM MCUs.

my code is 

// Set the clocking to 50 mhz.
SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);

RTCWrite(0x68,0,0x80); //set ST bit
RTCWrite(0x68,0,0x00); //clear ST bit
while(1)
{
get = ReadRTC(0x68,0);
UARTCharPut(UART0_BASE,get);
SysCtlDelay(SysCtlClockGet()/3);
}

Hi Swati,

swati arora said:

get = ReadRTC(0x68,0);

    I suspect this line above is causing an additional 1 second.

    Try commenting out that line and print out a single character at your serial console(e.g Terra Term).  See, if you still get a 2 second delay. 

-kel

i have tried it also...still i am getting 2 second delay....i think this is the problem of sysctldelay() function...is it????

swati arora said:

i think this is the problem of sysctldelay() function

You are setting it right for 1 second. I don't have your setup. But, I tried that using my Stellaris Evaluation kit. I set the clock at 50 Mhz and just printed out a single character at my Terra Term. I got a 1 second print out interval. This is the code I used below. I used the uart_echo as base. 

//50Mhz
SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
SYSCTL_XTAL_8MHZ);

while(1)
{
     UARTSend((unsigned char *)"A", 1);
     SysCtlDelay(SysCtlClockGet()/3);
}

-kel

so is it my hardware problem???

Is your board a custom board? You can probe your crystal to check, if you are getting the right frequency.

-kel

i have checked the crystal frequency by calling SysCtlClockGet function and it is right i.e.50mhz

Hi Swati,

   Sorry, I am out of ideas, at this point. Some additional questions below.

1. Is your board a custom board, Tiva Launchpad, Tiva Evaluation Kit, or Tiva Development kit?
2. Did you make a new project?
3. What tool chain are you using Keil? CCS? IAR Workbench?

swati arora said:

checked the crystal frequency by calling SysCtlClockGet function and it is right i.e.50mhz

Unlikely - your post seeks precision - yet you mix System Clock (50MHz) w/xtal frequency - above...

Both here have avoided vendor's comment that, "timing function in play" - is not - at all times - "Good for Gov't work."  As past suggested by vendor (confirmed by our group) precision results from use of a Timer - you trade program ease for precision - and then complain...

And - you hold hostage your delay function by its forced enslavement w/in UART transfer.  This provides the means to "spoil" your delay function - does it not?

Quick toggle of an Led provides a less "intrusive" means to monitor that delay...  (uncertain as it is)

i am using keil of toolchain  MDK-ARM standard version 4.54.0.0.

and my board is custom board

cb1_mobile  -  i dont think so that uart transfer is spoiling my "delay". and i cant check it other way or by means of led because in my custom board i do not have any led.

 by using SysCtlDelay(SysCtlClockGet()/ 3)  function i am getting 2 second of delay but by using ROM_SysCtlDelay(ROM_SysCtlClockGet()/ 3) function i am getting right delay of 1 second.now how it can be possible please explain me.

swati arora said:

by using SysCtlDelay(SysCtlClockGet()/ 3)  function i am getting 2 second of delay but by using ROM_SysCtlDelay(ROM_SysCtlClockGet()/ 3) function i am getting right delay of 1 second.now how it can be possible please explain me.

Nuno Dias said:

I was using the SysCtlDelay function to generate delays of 5 seconds but I got delays of about 10 seconds. I noticed this problem only happened when I used Keil. I didn't have this problema in CCS.

One possible reason for the differences between Keil and CCS is that the SysCtlDelay() delay can vary according to alignment. Previous experiments have shown that changing the alignment of the SysCtlDelay() function in flash can change the delay if the instructions cross a flash pre-fetch buffer boundary.