Raspberry Pi 5 - All channels on pwm0

README.md

Hardware PWM on the Raspberry Pi 5 b

Since PWM is a little fraught with gotchas, this is mostly a message to future me-

(Note to self, rtfm - https://datasheets.raspberrypi.com/rp1/rp1-peripherals.pdf)

pin	a0	a3
GPIO19		PWM0_CHAN3
GPIO18		PWM0_CHAN2
GPIO15	PWM0_CHAN3
GPIO14	PWM0_CHAN2
GPIO13	PWM0_CHAN1
GPIO12	PWM0_CHAN0

TODO: Figure out how to tell if pwm0 is on /sys/class/pwm/pwmchip1 or /sys/class/pwm/pwmchip2. pwm1 on the Pi 5 might have device/consumer:platform:cooling_fan/

Life is short, this single dtoverlay configures GPIO12, GPIO13, GPIO18 and GPIO19 to their respective alt modes on boot and enables pwm0:

/dts-v1/;
/plugin/;

/{
	compatible = "brcm,bcm2712";

	fragment@0 {
		target = <&rp1_gpio>;
		__overlay__ {
			pwm_pins: pwm_pins {
				pins = "gpio12", "gpio13", "gpio18", "gpio19";
				function = "pwm0", "pwm0", "pwm0", "pwm0";
			};
		};
	};

	fragment@1 {
		target = <&rp1_pwm0>;
		frag1: __overlay__ {
			pinctrl-names = "default";
			pinctrl-0 = <&pwm_pins>;
			status = "okay";
		};
	};
};

Save as "pwm-pi5-overlay.dts" and compile with:

dtc -I dts -O dtb -o pwm-pi5.dtbo pwm-pi5-overlay.dts

Install:

sudo cp pwm-pi5.dtbo /boot/firmware/overlays/

Don't forget to add dtoverlay=pwm-pi5 to /boot/firmware/config.txt...

Then use this janky script to stick some safety rails on poking PWM:

#!/bin/bash
NODE=/sys/class/pwm/pwmchip1
CHANNEL="$1"
PERIOD="$2"
DUTY_CYCLE="$3"

function usage {
	printf "Usage: $0 <channel> <period> <duty_cycle>\n"
	printf "    channel - number from 0-3\n"
	printf "    period - PWM period in nanoseconds\n"
	printf "    duty_cycle - Duty Cycle (on period) in nanoseconds\n"
	exit 1
}

if [[ ! $CHANNEL =~ ^[0-3]+$ ]]; then
	usage
fi

if [ -d "$NODE/device/consumer:platform:cooling_fan/" ]; then
	echo "Hold your horses, looks like this is pwm1?"
	exit 1
fi

if [ ! -d "$NODE/pwm$CHANNEL" ]; then
	echo "0" | sudo tee -a "$NODE/export"
fi

echo "0" | sudo tee -a "$NODE/pwm$CHANNEL/enable" > /dev/null
echo "$PERIOD" | sudo tee -a "$NODE/pwm$CHANNEL/period" > /dev/null
if [ $? -ne 0 ]; then
	echo "^ don't worry, handling it!"
	echo "$DUTY_CYCLE" | sudo tee -a "$NODE/pwm$CHANNEL/duty_cycle" > /dev/null
	echo "$PERIOD" | sudo tee -a "$NODE/pwm$CHANNEL/period" > /dev/null
else
	echo "$DUTY_CYCLE" | sudo tee -a "$NODE/pwm$CHANNEL/duty_cycle" > /dev/null
fi
echo "1" | sudo tee -a "$NODE/pwm$CHANNEL/enable" > /dev/null


case $CHANNEL in
	"0")
	PIN="12"
	FUNC="a0"
	;;
	"1")
	PIN="13"
	FUNC="a0"
	;;
	"2")
	PIN="18"
	FUNC="a3"
	;;
	"3")
	PIN="19"
	FUNC="a3"
esac

# Sure, the pin is set to the correct alt mode by the dtoverlay at startup...
# But we'll do this to protect the user (me, the user is me) from themselves:
pinctrl set $PIN $FUNC

echo "PWM$CHANNEL set to $PERIOD ns, $DUTY_CYCLE, on pin $PIN (func $FUNC)."

Possibly a better way to handle the script:

#!/bin/bash
NODE=/sys/class/pwm/pwmchip1
PIN="$1"
FUNC="a0"
PERIOD="$2"
DUTY_CYCLE="$3"

function usage {
	printf "Usage: $0 <channel> <period> <duty_cycle>\n"
	printf "    pin - one of 12, 13, 14, 15, 18 or 19\n"
	printf "    period - PWM period in nanoseconds\n"
	printf "    duty_cycle - Duty Cycle (on period) in nanoseconds\n"
	exit 1
}

if [ -d "$NODE/device/consumer:platform:cooling_fan/" ]; then
	echo "Hold your horses, looks like this is pwm1?"
	exit 1
fi

case $PIN in
	"12")
	CHANNEL="0"
	;;
	"13")
	CHANNEL="1"
	;;
	"14")
	CHANNEL="2"
	;;
	"15")
	CHANNEL="3"
	;;
	"18")
	CHANNEL="2"
	FUNC="a3"
	;;
	"19")
	CHANNEL="3"
	FUNC="a3"
	;;
	*)
	echo "Unknown pin $PIN."
	exit 1
esac

function pwmset {
	echo "$2" | sudo tee -a "$NODE/$1" > /dev/null
}

if [[ "$PERIOD" == "off" ]]; then	
	if [ -d "$NODE/pwm$CHANNEL" ]; then
		pinctrl set $PIN no
		pwmset "pwm$CHANNEL/enable" "0"
		pwmset "unexport" "$CHANNEL"
	fi
	exit 0
fi

if [[ ! $PERIOD =~ ^[0-9]+$ ]]; then
	usage
fi

if [[ ! $DUTY_CYCLE =~ ^[0-9]+$ ]]; then
	usage
fi

if [ ! -d "$NODE/pwm$CHANNEL" ]; then
	pwmset "export" "$CHANNEL"
fi

pwmset "pwm$CHANNEL/enable" "0"
pwmset "pwm$CHANNEL/period" "$PERIOD"
if [ $? -ne 0 ]; then
	echo "^ don't worry, handling it!"
	pwmset "pwm$CHANNEL/duty_cycle" "$DUTY_CYCLE"
	pwmset "pwm$CHANNEL/period" "$PERIOD"
else
	pwmset "pwm$CHANNEL/duty_cycle" "$DUTY_CYCLE"
fi
pwmset "pwm$CHANNEL/enable" "1"

# Sure, the pin is set to the correct alt mode by the dtoverlay at startup...
# But we'll do this to protect the user from themselves:
pinctrl set $PIN $FUNC

echo "GPIO $PIN (Ch. $CHANNEL, Fn. $FUNC) set to $PERIOD ns, $DUTY_CYCLE."

Kind soul, thank you for this, I tried many different solutions, including using the raspian devicetree overlays and directly setting memory-mapped registers to no avail. Your solution was the only one that worked, and it worked out of the box for me.

It's crazy to think it is this difficult to unlock PWM, and that there isn't a better tutorial for it.

In my case my chip was pwmchip2 (I also had a pwmchip0 and pwmchip6)