UART IRQ fails to update TPM0_C1V

johnconnor — Sat, 03 Feb 2018 18:04:48 GMT

Hello, I have 2 FRDM KL25Z boards which I am using as a Tx board (with Potentiometer and ADC + UART0 TX), and an Rx board (with a hobby servo connected to UART0 RX).

Basically, one board performs ADC on the Pot, and sends it over via UART0 to the other board, the other board modulates duty cycle based on input from UART0. Both are driven by simple ISRs.

I'm getting good UART0_D values from the Tx board (tested by using output to toggle the tricolor LED pins as GPIO), but when trying with PWM, TPM0_C1V will not update as I expect it to with the UART ISR.

Can anyone tell me why TPM0_C1V does not get updated as I move the pot in the following Rx'er code, or provide some tips for further debugging?

#include <MKL25Z4.h>

void UART0_init(void);
void PWM_init(void);

int main(void) {

   SystemCoreClockUpdate();

   __disable_irq();

   UART0_init();           // set up UART
   PWM_init();               // set up TPM0

   __enable_irq();       // call global IRQ handler

   while(1) {

       // UART0 Rx & TPM0_C1V updates done by ISR
   }

}

void UART0_IRQHandler(void) {

   int c = UART0_D;               // UART_D generates 8 bit values 0-255,
   TPM0_C1V = 400 + (c);       // C1V range of 400 - 655 for roughly ~1ms - 2ms pulse width

}

void UART0_init(void) {

   SIM_SOPT2 |= SIM_SOPT2_PLLFLLSEL(1);               // choose PLL output for UART baud rate calc
   SIM_SOPT2 &= ~SIM_SOPT2_UART0SRC_MASK;
SIM_SOPT2 |= SIM_SOPT2_UART0SRC(1);                 // PLL source
   SIM_SCGC4 |= SIM_SCGC4_UART0_MASK;           // enable clock to UART0

   UART0_C2 = 0;                                               // turn off UART0 while changing configuration

   UART0_BDH = 0;                                           // zero out BDH
    UART0_C4 = 16;                                               // 16 samples
   UART0_BDL = 26;                                           // 48mhz with 16samples divide by 26 gives ~115200 baud
   UART0_C1 = 0;                                               // has effect of choosing 8 bit data stream

   UART0_C2 = UART0_C2_RIE_MASK | UART0_C2_RE_MASK;       // enable Rx and RIE UART0
   NVIC->ISER[0] |= 0x00001000;               // enable int 12 (bit 12 of ISER[0] -- UART0 IRQ on NVIC

   SIM_SCGC5 |= SIM_SCGC5_PORTA_MASK;   // Clock to PortA
   PORTA_PCR1 = PORT_PCR_MUX(2);            // Set ALT2 for PortA PCR1 (UART0_RX)

}

void PWM_init(void) {

    SIM_SCGC6 |= SIM_SCGC6_TPM0_MASK;                 // Clock TPM0
   SIM_SCGC5 |= SIM_SCGC5_PORTC_MASK;              // Clock to Port C(TPM output on PTC2)

   SIM_SOPT2 |= SIM_SOPT2_TPMSRC(1);                   // 1 is PLL Clock @48MHz

   PORTC_PCR2 = PORT_PCR_MUX(4);                // set to PWM TPM0_CH1 ALT function for IO pin PTC2

   TPM0_SC = TPM_SC_CMOD(1) | TPM_SC_PS(7);      // 48MHz clock at 128 prescaler for 375kHz
   // status control register for TPM0: set clock mode to increment counter on every LPTPM tick

   TPM0_CNT = 0;                                   // write to CNT as per datasheet
   TPM0_MOD = 7500;                           // 7500 (48MHz / 128(prescaler) / 7500cycles) = 50hz, 20 ms period
   TPM0_C1SC = TPM_CnSC_MSB_MASK | TPM_CnSC_ELSA_MASK;

}

Thank you!

Re: UART IRQ fails to update TPM0_C1V

Robin_Shen — Fri, 09 Feb 2018 08:01:11 GMT

Hi John,

Please try to use the function below:

static volatile uint8 c;
void UART0_IRQHandler(void) {
   if (UART0_S1&UART_S1_RDRF_MASK)
   {
       c = UART0_D;                // UART_D generates 8 bit values 0-255,
       TPM0_C1V = 400 + (c);        // C1V range of 400 - 655 for roughly ~1ms - 2ms pulse width
   }
}

Best Regards,

Robin

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UART IRQ fails to update TPM0_C1V

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