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Hardware PWM


The Omega's SoC has several PWM modules. The Omega2 exposes 2 hardware PWM channels on its pin headers while the Omega2S exposes 4.


Pulse-width modulation (PWM) is a technique of producing varying analog signals from a digital source.

  • Duty cycle = percentage of time the signal is high (0-100).
  • Frequency = signal frequency.


In this section we are referring to hardware-based PWM modules.

Omega2/2+: 2 channels, Omega2S/2S+: 4 channels

The hardware PWM modules have a frequency range of 39Hz to 40MHz. For lower frequencies it is recommended to consider an external hardware PWM generator or the use of a software generated PWM signal from a GPIO pin.

PWM ChannelGPIONotes
2GPIO20Omega2S only
3GPIO21Omega2S only

The PWM pins are highlighted on the Omega2/2S diagrams below.

omega2-pinout pwm pins


The following sections discuss enabling and working with the hardware PWM.

Enabling Hardware PWM

To enable the use of hardware PWM, a kernel module needs to be installed:

opkg update   
opkg install kmod-pwm-mediatek-ramips

Adjusting pin multiplexing to enable PWM pins

The Omega's pins are multiplexed allowing the exposed pins to be used for several different functions.

The pin multiplexing configuration can be easily changed from the command line using omega2-ctrl.

For GPIO18:

omega2-ctrl gpiomux set pwm0 pwm

For GPIO19:

omega2-ctrl gpiomux set pwm1 pwm

For GPIO20 (Omega2S only):

omega2-ctrl gpiomux set uart2 pwm23

For GPIO21 (Omega2S only):

omega2-ctrl gpiomux set uart2 pwm23

The multiplexing configuration will need to be repeated after each reboot of the Omega2.

Generating PWM signals

To generate PWM signals, we'll need to install the omega2-script package.

opkg update
opkg install omega2-script

Once the pins have been configured for PWM usage, we can configure the PWM hardware module to generate a PWM signal using the following command:



  • CHANNEL is 0 (GPIO18), 1 (GPIO19), 2 (GPIO20), or 3 (GPIO21).
    • Remember that channels 2 & 3 are exposed on the Omega2S only.
  • DUTY_CYCLE is the percentage of time the signal is ON, expressed 0-100
  • FREQUENCY is the signal frequency, expressed in Hz.

Stopping the PWM signal

To stop and disable the PWM signal:

onion pwm <CHANNEL> disable

The omega2-script provides a helpful wrapper around sysfs for PWM. The source code is available at