S32K148 time measuring using LPTMR

[tomasfrcek]

Hello,

I'm trying to configure the LPTMR module of S32K148 on our custom board to measure time between function calls StartTimeMeasurement and StopTimeMeasurement.

This is my configuration so far:

// Deactivates module clock before modification.
PCC->PCCn[PCC_LPTMR0_INDEX] &= PCC_PCCn_CGC_MASK;
    
// Sets SOSCDIV2_CLK as module clock source (we are using 8MHz crystal).
PCC->PCCn[PCC_LPTMR0_INDEX] &= PCC_PCCn_PCS_MASK;
PCC->PCCn[PCC_LPTMR0_INDEX]  |= PCC_PCCn_PCS(1U);

// FRAC and PCD = 0. This should result in module input clock 8MHz.

PCC->PCCn[PCC_LPTMR0_INDEX] &= ~(PCC_PCCn_FRAC_MASK | PCC_PCCn_PCD_MASK);

// Reactivates module clock.
PCC->PCCn[PCC_LPTMR0_INDEX] |= PCC_PCCn_CGC(1U);

// Deactivates module before initialization.
LPTMR0->CSR &= ~LPTMR_CSR_TEN_MASK;
    
// Prescale Bypass - module clock source directly feeds the counter register. Set PCC_CLK as module source clock.
LPTMR0->PSR = LPTMR_PSR_PBYP(1U) | LPTMR_PSR_PCS(3U);
    
// Counter register counts to the highest possible value before generating interrupt.
LPTMR0->CMR = 0xFFFF;
    
// Sets module to function in the timer counter mode, counter register to clear when TCF is set and activates interrupt.
LPTMR0->CSR = LPTMR_CSR_TCF(1U) | LPTMR_CSR_TIE(1U) | LPTMR_CSR_TFC(0U) | LPTMR_CSR_TMS(0U);

// Activates module.

LPTMR0->CSR |= LPTMR_CSR_TEN(1U);

I see all the registers setup in the debugger, however the timer counter register value does not increment.

Thank you for any advice!

[danielmartynek]

Hi,

I don't see any problem in the code.

Please check if SOSC is enabled.

Have you tried with a different clock source? 

The counter doesn't increment in when the core is halted.

Regards,

Daniel

[tomasfrcek]

Hello, Daniel,

Thank you for your reply. I already tried to switch from SOSCDIV2 to SPLLDIV2:

PCC->PCCn[PCC_LPTMR0_INDEX] &= PCC_PCCn_PCS_MASK;
PCC->PCCn[PCC_LPTMR0_INDEX]  |= PCC_PCCn_PCS(6U);

However the counter still doesn't count (register CNR remailns 0x0). I know that both clocks SOSCDIV2 and SPLLDIV2 work as I'm already feeding them to CAN (SOSCDIV2) and CAN FD (SPLLDIV2) modules Protocol Engines in the same project and communication works.

Tomas

[danielmartynek · Accepted solution]

Hello Tomas,

I have found the reason it returns 0.

The CNR returns the current value of the LPTMR counter at the time this register was last written.

So, you need to write to the register first.

It will synchronize the register with the counter

LPTMR0->CNR = 0x0001;
uint32_t cnr = LPTMR0->CNR;‍‍

Regards,

Daniel

[tomasfrcek]

Hello, Daniel,

thank you, It works! Serves me right for not paying attention to the manual :smileyhappy:

Regards,

Tomas