FTM settings on KEA

[hanisamara]

Hello all,

i am trying to setup the FTM modul to generate 50us interrupt. The FTM works with 48MHz and i select a prescaler of 64. that means the timer has a period of 1.3333us. So to have 50us i shoul set the channel counter (FTMx_CxV) to 37. But what i measure is an 25us interrupt?? it looks like the FTM clock source is 24MHz and not 48MHz! here ist hte Clock setting and the FTM init code:

void clk_init(void){   
    ICS_C2 |=ICS_C2_BDIV(1);    /* default BDIV=2 */                                                           
    SIM_CLKDIV = (SIM_CLKDIV_OUTDIV1(0x00) | SIM_CLKDIV_OUTDIV2_MASK); /* core clk 48MHz, Bus clk 24MHz,    Timer clk 48MHz */
    ICS_C1 |=ICS_C1_IRCLKEN_MASK; /* Enable the internal reference clock */                                                            
    ICS_C1 |=ICS_C1_IREFS_MASK;    /* select internal clock as source for FLL */
    ICS_C1 |= ICS_C1_CLKS(0);    /* select FLL output as source for Bus frequency */
  

    ICS_C2 |= ICS_C2_BDIV(0);  /* BDIV = 1 */
    ICS_C2 &= ~(uint8_t)ICS_C2_LP_MASK;
   
    OSC_CR = 0x00U; /* disable OSC Module */
    while((ICS_S & ICS_S_IREFST_MASK) != 0x10U) { /* Check that the source of the FLL reference clock is the internal         reference clock. */
    }
    while((ICS_S & 0x0CU) != 0x00U) {    /* Wait until output of the FLL is selected */
    }
}

void FTM2_Init(void){

    SIM_SCGC |= SIM_SCGC_FTM2_MASK;    /* enable clock for FTM0 _Freescale_*/
    FTM2_SC |= FTM_SC_PS(6);    /* select prescaler -> 64 _Freescale: Value adjusted_*/
    FTM2_C0SC |= FTM_CnSC_CHIE_MASK; /* enable channel 0 interrupt _Freescale_*/
    FTM2_C0SC |= FTM_CnSC_MSA_MASK; /* channel works in output compare mode _Freescale_*/
    FTM2_C0V = 37;    /* every 50µs */    
    FTM2_SC  |= FTM_SC_CLKS(1);    /* FTM0 uses system clock _Freescale_*/
}

what could be the problem? if i assume that the Timer clk is 24MHz every thing works fine.

thank you for helping.

Hani

[Robin_Shen]

Hi Hani,

Since you are using KEA ZN8, Timer clock(ICSOUTCLK divided by DIV3) clocks the FTM and PWT modules.

You need to check whether the SIM_CLKDIV[OUTDIV3] and ICS_C2[BDIV] are correct configured.

I didn't see the SIM_CLKDIV_OUTDIV3 in clk_init().

You can't set the value of BDIV like that. Since the BDIV is default to 0x01, it will still equal to 0x01.

Best Regards,

Robin

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[hanisamara]

Hello Robin,

Thank you for answer.

for OUT_DIV3 i set it many times to 0, but it dose not help.

for the BDIV i set it in the code to be zero, i.e. ICSOUTCLK divided by one. (ICS_C2 |= ICS_C2_BDIV(0)).

My configuration:

1. FLL out = 48MHz

2. BDIV = 1 default divide by 2

3. ICSOUTCLK = 24MHz

4. DIV1=0 (divide by 1)

5. DIV2=1 (divide by 2)

6. DIV3=0 (divide by1)

7. BDIV = 0 (divide by 1) --> ICSOUTCLK = 48MHz

         -- FTM/PWT clk = 48MHz

         -- Core clk = 48MHz

         -- Bus clk = 24MHz

but as i told Mark in the previous Post, i donot understand why we should enable the bus clk for the FTM in the FTM init code??! (SIM_SCGC |= SIM_SCGC_FTM2_MASK;    /* enable bus clock for FTM0 _Freescale_*/) 

if i remove this line the timer did not started at all!

Regards

Hani

[Robin_Shen · Accepted solution]

Hi Hani,

Please refer the code shown below:

/* ICS_C2: BDIV=0,LP=0 */
  ICS_C2 &= (uint8_t)~(uint8_t)((ICS_C2_BDIV(0x07) | ICS_C2_LP_MASK));

Best Regards,

Robin

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[hanisamara]

Hello Robin,

Thank you very much. You are right, it is an OR operation, so the 0x01 still remains. It works fine now.

Best Regards,

Hani

[mjbcswitzerland]

Hani

The timer module in the Kinetis KEA parts is clocked from the BUS clock, which you have set to 24MHz.

If you are getting values for a 24MHz clock it sounds as though all is normal.

Regards

Mark

[hanisamara]

Hallo Mark,

thank you.

in the reference manual as you can see in Robin post, you can configure the FTM/PWT to have 48MHz! but what this line means in the FTM_init:

SIM_SCGC |= SIM_SCGC_FTM2_MASK;    /* enable clock for FTM0 _Freescale_*/

it enables the bus clock for the the FTM modul?! i took this code from Freescale getting started document.

Regards 

Hani