topic KL03 TPM: CMOD gets changed to zero each time TPM_DRV_PwmStart() runs in Kinetis Software Development Kit

KL03 TPM: CMOD gets changed to zero each time TPM_DRV_PwmStart() runs

aes_mike — Tue, 03 Jan 2017 13:35:33 GMT

It seems that each time the TPM_DRV_PwmStart() is run that the TPM0.SC.CMOD gets set to zero. As a result the PWM output never changes at pin PTA6. Attached is a screen shot. If I set a breakpoint just after the TPM_DRV_PwmStart() and then change CMOD back to 0x1, then it works fine. It is not clear to me why CMOD reverts to zero after TPM_DRV_PwmStart()? Any suggestions? I just want to be able to adjust the PWM output at any time. I am not real familiar with the TPM, so some of this might be just misunderstanding how it works.

I have setup the TPM0 as a PWM output.

tpm_general_config_t main_tpm_config;

tpm_pwm_param_t main_tpm_timer_channel_config = {
.mode = kTpmEdgeAlignedPWM,
.edgeMode = kTpmHighTrue,
.uFrequencyHZ = 100000U,
.uDutyCyclePercent = 50U,
};

Initialization portion:

CLOCK_SYS_SetTpmSrc( TPM0_IDX, kClockTpmSrcIrc48M );
TPM_DRV_Init( TPM0_IDX, &main_tpm_config );
TPM_DRV_SetClock( TPM0_IDX, kTpmClockSourceModuleClk, kTpmDividedBy2 );
main_tpm_timer_channel_config.uDutyCyclePercent = 50;
TPM_DRV_PwmStart( TPM0_IDX, &main_tpm_timer_channel_config, 0U );

Software: KDS 3.0.0, KSDK 1.3.0.

Re: KL03 TPM: CMOD gets changed to zero each time TPM_DRV_PwmStart() runs

aes_mike — Tue, 03 Jan 2017 15:54:27 GMT

Also, as I sweep the PWM from 0 to 100, incrementing the PWM by one each second, I notice that the output frequency will vary from 100KHz, 366Hz or DC. In other words, it does not seem to be operating in a PWM mode from perspective of the output at PTA6. Mike.

Re: KL03 TPM: CMOD gets changed to zero each time TPM_DRV_PwmStart() runs

xiangjun_rong — Wed, 04 Jan 2017 06:25:18 GMT

Hi,

As you know that condition the TPM counts tick is that the CMOD bits can not be 0 or 3. So before you call the TPM_DRV_PwmStart(), you have to call TPM_DRV_SetClock(BOARD_BUBBLE_TPM_INSTANCE, kTpmClockSourceModuleClk, kTpmDividedBy2);

The TPM_DRV_SetClock() can assign the kTpmClockSourceModuleClk to a global variable so that the global variable can set up the CMOD bits in TPM_DRV_PwmStart().

//BOARD_BUBBLE_TPM_INSTANCE=0;

Hope it can help you

XiangJun Rong

Re: KL03 TPM: CMOD gets changed to zero each time TPM_DRV_PwmStart() runs

aes_mike — Fri, 06 Jan 2017 19:57:16 GMT

To close out this question and help others out there struggling with similar issue, it turns out that the issue is a stack overflow problem which is clobbering the global variable (s_tpmClockSource) that you mentioned. I setup a watchpoint on that variable and sure enough it was being change in unexpected ways. That is why the PWM appears to come and go because the s_tpmClockSource is used to write to CMOD anytime TPM_DRV_PwmStart() is run.

I now have set a watchpoint at the bottom of the stack and that has helped as well as using the -fstack_usage flag for the GCC compiler which produces a report on the stack foot print of each function that is compiled.