Learn how to use Pulse Width Modulation (PWM) on Portenta X8.
Note
The PWM pins on Portenta X8 are exposed via the high-density connector interface. A compatible carrier board (such as the Portenta Breakout) is recommended. When Portenta X8 is connected to a carrier board, each channel corresponds to the PWMx pin on the carrier board.
1. Connect to the Linux shell
Connect to the Linux shell using Android Debug Bridge
2. Export a new channel
Porenta X8 has 10 PWN channels (enumerated 0-9). They can be controlled with the sysfs interface.
Export a new PWM channel with this command (replace <channel number> with a pin number).
echo <channel number> > /sys/class/pwm/pwmchip0/export
For example, to use pin PWM2, run this command:
echo 2 > /sys/class/pwm/pwmchip0/export
After exporting the PWM channel, navigate to its directory using cd pwmX, where X represents the channel number you exported (e.g., cd pwm2).
| Pin | Path |
|---|---|
| PWM0 | /sys/class/pwm/pwmchip0/pwm0 |
| PWM1 | /sys/class/pwm/pwmchip0/pwm1 |
| PWM2 | /sys/class/pwm/pwmchip0/pwm2 |
| PWM3 | /sys/class/pwm/pwmchip0/pwm3 |
| PWM4 | /sys/class/pwm/pwmchip0/pwm4 |
| PWM5 | /sys/class/pwm/pwmchip0/pwm5 |
| PWM6 | /sys/class/pwm/pwmchip0/pwm6 |
| PWM7 | /sys/class/pwm/pwmchip0/pwm7 |
| PWM8 | /sys/class/pwm/pwmchip0/pwm8 |
| PWM9 | /sys/class/pwm/pwmchip0/pwm9 |
3. Open the channel directory
Navigate to the channel directory that was created when you exported the channel:
cd /sys/class/pwm/pwmchip0/pwm<channel number>
For example:
cd /sys/class/pwm/pwmchip0/pwm2
4. Configure a channel
When you’ve exported the channel and navigated into the channel directory, you can configure the PWM channel:
enable
The enable property is used to enable/disable the PWM signal.
Enable the PWM output:
echo 1 > enable
Disable the PWM output:
echo 0 > enable
Check if the channel is enabled:
cat enable
period
Note
Period needs to have a higher value than duty cycle.
Represents the total duration of the PWM signal, including both the active (ON) and inactive (OFF) periods.
You configure this by running echo x > period, where x, in this case, is the desired duration in nanoseconds.
Set the period of the PWM signal to x nanoseconds:
echo x > period
Check current period value:
cat period
duty_cycle
Represents the percentage of time the signal is in the active (ON) state during each period.
You configure this by running echo x > duty_cycle, where x, in this case, is the desired duration in nanoseconds.
Set duty cycle to x nanoseconds:
echo x > duty_cycle
Check current cycle value:
cat duty_cycle
Troubleshooting
If the export command fails, try running sudo su -. Then, navigate back to the PWM configuration directory using cd /sys/class/pwm/pwmchip0.
Alternatively, try writing sudo before the command.
