Is it possible to use two PWM channels independently?

[James Fitzsimons]

Hi all,

I've got pwm working both through echoing values directly to the device files from bash, and also via my C++ program. However I can't get two channels of a epwmss device to operate independently. e.g. If I export both 

/sys/devices/platform/ocp/48300000.epwmss/48300200.pwm/pwm/pwmchip1/pwm-1:0 and pwm-1:1 then set a value for period and duty on either one of the channels (pwm-1:0 or pwm-1:1), as soon as I enable that channel both channels start. Stopping the channel stops both channels. I've even tested starting one channel then stopping the other and both stop.

I had read elsewhere that both channels had to use the same frequency (period), which would work for my application, however I need to be able to set the duty cycle and enable/disable independently. Is that possible?

I'm using the 4.14.20-ti-r36 kernel and have the following overlays enabled:

uboot_overlay_addr6=/lib/firmware/am33xx_pwm-00A0.dtbo

uboot_overlay_addr7=/lib/firmware/BB-PWM0-00A0.dtbo

I'll go read the Technical Reference Manual now, but if someone can shed some light on this for me it would be much appreciated!

Cheers,

James Fitzsimons

[evilwulfie]

Thee are 6 pwm channels

3 pairs use the same frequency but all can have independent duty cycles

Pick one each from different group for your application

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[TJF]

You can generate PWM outputs by

• 2x3 channels on the PWM modules in the PWMSS
• 3 channels on the CAP modules in the PWMSS (P9_28, P9_42, JT_05=5V)
  
• 4 channels on TIMER 4 to 7 (P8_07, P8_08, P8_09, P8_10
• 1 channel on CAP module in the PRU (P8_15)
  

In case of the PWM modules the A and B channel operates at the same frequency (and start at the same time). In order to switch a channel off, you can set the duty cycle to 0 (zero).

All other outputs can operate independendly (duty cycle, frequency and start time).

[James Fitzsimons]

Thanks very much guys, I now understand the limitations of the epwmss better. 

After giving it some more thought, I think I should be able to get by without having the need to switch either the A or B output off independently. Varying the duty cycle should be sufficient.

Thanks again,

James Fitzsimons

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