topic Re: What is PWM range when using eTPU function? (MPC5644A) in MPC5xxx

What is PWM range when using eTPU function? (MPC5644A)

JinwooLim — Tue, 07 Nov 2023 07:48:16 GMT

Hi, i am trying to generate PWM signal using eTPU function. (MPC5644A)

the function i am currently uing is fs_etpu_pwm_update()

based on local parameter in this funciton, when the value of (chan_period*duty)/10000 gets over 426000 the generated PWM signal doesnt show up properly.

the estimated problem is data overflow when trying write parameter value to data memory.

how can i solve this problem?? and how can i generate full range pwm signal??

ps. i was trying to generate 250Hz, 80% duty but it didnt worked. and i realized memory overflow is happening somewhere between 250Hz 71~72% duty. which is 426000~432000 in ((chan_period*duty)/10000) value.

Re: What is PWM range when using eTPU function? (MPC5644A)

davidtosenovjan — Wed, 08 Nov 2023 12:28:34 GMT

Could you clarify which specific eTPU function is your question related to? Thanks

Re: What is PWM range when using eTPU function? (MPC5644A)

JinwooLim — Wed, 08 Nov 2023 23:15:06 GMT

the name of funtion is "fs_etpu_pwm_update(channel, frequency, duty, timebase frequency)"

this function is in "etpu_pwm.c" file which is written by Jeff Loeliger, Revision is 2.0

thanks

Re: What is PWM range when using eTPU function? (MPC5644A)

KarlP — Thu, 09 Nov 2023 08:17:32 GMT

I might be wrong but it looks like you have the etpu tcr1 or tcr2 set with a high frequency clock so generating a low frequency signal (250Hz) from that clock with a 24-bit count limit is causing a problem.

Try adjusting the prescaler for the TCR used to lower the timebase frequency, e.g. down to 4MHz. Set the fs_etpu_pwm_init to that new frequency as well as in fs_etpu_pwm_update.

Re: What is PWM range when using eTPU function? (MPC5644A)

KarlP — Thu, 09 Nov 2023 08:38:15 GMT

p.s. if I work your numbers backward it appears that you have the timebase_freq set to 150MHz (system clock). This is causing the overlfow within the fs_etpu_pwm_update function.

The timebase_freq should be the TCR1 or TCR2 clock frequency, and that will need to be prescaled down to something more suitable so the 24-bit TCR counter works with your output frequency/resolution needs.

Re: What is PWM range when using eTPU function? (MPC5644A)

JinwooLim — Fri, 10 Nov 2023 03:51:41 GMT

Hi. First of all Thanks for the precise reply.

basically i have only used fs_etpu_pwm_update() function without fs_etpu_pwm_init() funciton.

would that mean if i do not use fs_etpu_pwm_init() function, etpu pwm is initialized automatically with TCR1 150MHz time base frequency?

And the "Prescale down" you mentioned, can be done by modifying function timebase frequency input from TCR1 to TCR2?

Re: What is PWM range when using eTPU function? (MPC5644A)

JinwooLim — Fri, 10 Nov 2023 06:39:38 GMT

i have tried changing timebase freqeuncy from etpu_a_tcr1_freq(150MHz) to etpu_a_tcr2_freq(18750000) as input of fs_etpu_pwm_init(), fs_etpu_pwm_update() functions.

but the pwm signal doesnt show up..

should i change eTPU timebase frequency register settings somewhere??