TM4C1290NCPDT: Main clock seems to be running 25% slow.

Hi Doug,

  First of all, what does the ClockSpeed variable return? Is it 20000000?

Yes

A couple of questions:

- Can you measure your MOSC? is it is truly 20Mhz?

- What does UARTIBRD and UARTFBRD registers show?

- What does your function GetClkSpeed() return?

- Why are you passing GetClkSpeed() to UARTConfigSetExpClk()  instead of ClockSpeed which you said is equal to 20000000?

Yes, the oscillator is running at 19.9999MHz

IBRD = 104, FBRD = 11

//----------------------------------------
//  INITIALIZE GLOBAL CPU CONFIGURATION  |
//---------------------------------------------------------------------------------------------------------------
//  Actual Clock Speed and Hardware Version
//
    static u32 ClockSpeed;
    static u8  HardwareVersion;
//
//---------------------------------------------------------------------------------------------------------------
//  GET CLOCK SPEED and HARDWARE VERSION

u32 GetClkSpeed(void)  { return(ClockSpeed); }

u8  GetHwVersion(void) { return(HardwareVersion); }

//---------------------------------------------------------------------------------------------------------------
//  We'll run the clock at 20MHz so there are no wait states in Flash and to save power.

void Init_CPU(void) {


    // *** NOTE *** Keep the clock rate set here in sync with CPU_CLK_SPEED in common.h

    ClockSpeed = SysCtlClockFreqSet(SYSCTL_USE_OSC | SYSCTL_OSC_MAIN | SYSCTL_XTAL_20MHZ, 20000000);   // 20MHz

I tried to enable DIVSCLK output to view the clock speed there but the pin just sits high.  Here's my code:

GPIOPinTypeDIVSCLK(GPIO_PORTG_BASE, PG_AccSDO_BIT);     // *TESTING*
SysCtlClockOutConfig(SYSCTL_CLKOUT_EN | SYSCTL_CLKOUT_MOSC, 2);

AccSDO_BIT is port G4.

Is there something else I need to do to get it to work?

Thanks, Doug

Hi,

Doug Broadwell85 said:

UARTConfigSetExpClk(UART0_BASE, GetClkSpeed(), 12000,
            ( UART_CONFIG_WLEN_8 | UART_CONFIG_STOP_ONE | UART_CONFIG_PAR_NONE ));

  You pick 12000 baudrate. This is not a standard UART baudrate I've seen. Below I'm showing typical supported baudrates from two serial terminal utility. The one that come closest to12000 is 14400 or 9600. Can you try a supported baudrate like 115200 or others. Do you see the same problem? 

Yes, I know 12000 is not a standard baud rate, but as I stated before, if I set it to 9600 the characters are 25% too slow and it doesn't work.  I set it to 12000 and the actual data stream is then 9600 baud.  The issue I'm having is that the clock going into the UART and SysTick is 25% too slow.

Thanks, Doug

As another aside, after discovering that SysTick didn't work if Vdd was 3.1 volts and VddA was 3.3 volts I did check and currently Vdd is 3.288 volts and VddA is 3.308 volts so I doubt that it could be causing the problem.

Hi Doug,

  Can you try? Does it make a difference?

g_ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_20MHZ |
SYSCTL_OSC_MAIN |
SYSCTL_USE_PLL
), 20000000);

Were you able to get the DIVSCLK to output anything other than high? If so what did you do? I've never been able to get that working.  Thanks.

No, but I had an errant 3.3 volt power supply that screwed up the CPU and caused it to do many weird things, so I don't know if my failure was not setting the software up correctly or the bad power supply.

Sorry.

Ridcrash said:

Were you able to get the DIVSCLK to output anything other than high? If so what did you do? I've never been able to get that working.

Can you try the below example code. 

MAP_GPIOPinConfigure(GPIO_PQ4_DIVSCLK);
GPIODirModeSet(GPIO_PORTQ_BASE, GPIO_PIN_4, GPIO_DIR_MODE_HW);
GPIOPadConfigSet(GPIO_PORTQ_BASE, GPIO_PIN_4, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD);
SysCtlClockOutConfig(SYSCTL_CLKOUT_EN | SYSCTL_CLKOUT_SYSCLK, 10);

No bother. Thanks.

This doesn't work. I've seen this earlier here:

e2e.ti.com/.../1971027

Is it not unusual that on an ek-tm4c1294exl PQ4 is connected to the power distribution switch (tps2052) and is pulled low if there's an over-current? How is this pin meant to output a clock?  

What am I missing?

Edit: ok i see this now:

https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/345762/tiva-c-series-tm4c1294-connected-launchpad

Understood.