user LED control on i.MX93 FRDM board

ilya_chepurin — Wed, 02 Sep 2026 15:05:22 GMT

Hi all,
I started to play with i.MX93 FRDM board and when I wrote a simple script to control RGB LEDs on the board, I've managed to control only Green and Blue LEDs. Red LED stays ON whatever I tried.
Based on the schematics, all leds are connected in a similar manner, so they operate Active High.
Here is my script:

---------------------------

#!/bin/sh

PERIOD=1000000

set_pwm() {
CHIP=$1
CHANNEL=$2
DUTY=$3
PWM_PATH="/sys/class/pwm/pwmchip${CHIP}/pwm${CHANNEL}"

if [ ! -d "$PWM_PATH" ]; then
echo "$CHANNEL" > "/sys/class/pwm/pwmchip${CHIP}/export" 2>/dev/null
fi

# Reset duty cycle to 0 first to satisfy TPM driver constraints
echo 0 > "${PWM_PATH}/duty_cycle" 2>/dev/null
echo "$PERIOD" > "${PWM_PATH}/period"
echo "$DUTY" > "${PWM_PATH}/duty_cycle"
echo 1 > "${PWM_PATH}/enable" 2>/dev/null
}

# Red is Active-Low: Default OFF = 1000000 (3.3V / High)
RED_DUTY=${1:-0}

# Green and Blue are Active-High: Default OFF = 0 (0V / Low)
GREEN_DUTY=${2:-0}
BLUE_DUTY=${3:-0}

# Red -> pwmchip4, Channel 3
set_pwm 4 3 "$RED_DUTY"

# Green -> pwmchip0, Channel 0
set_pwm 0 0 "$GREEN_DUTY"

# Blue -> pwmchip0, Channel 2
set_pwm 0 2 "$BLUE_DUTY"
-------------------------------------------

I've checked that red LED (GPIO_IO13) is allocated to the ledsgrp2:
pin 17 (IMX93_IOMUXC_GPIO_IO13): 424f0000.pwm (GPIO UNCLAIMED) function pinctrl group ledsgrp2

as far as I can see with debugfs commands, the pin GPIO_IO13 is configured for ALT1 mode, which is a TPM2 channel 3 (PWM).

when I run the script, I can successfully control Blue and Green LEDS but Red LED stays ON.

Is there something that I miss?

Re: user LED control on i.MX93 FRDM board

Zhiming_Liu — Thu, 03 Sep 2026 01:27:42 GMT

Hi @ilya_chepurin

The RED LED is channel 2, please use below script to test(verified on L6.18.20)

#!/bin/sh # RGB LED PWM cycle test for i.MX93 EVK/FRDM. # Sequence per cycle: RED on 1s -> all off 1s -> GREEN on 1s -> all off 1s -> BLUE on 1s -> all off 1s # Usage: ./run.sh [LOOPS] LOOPS: number of full cycles, 0 = infinite, default 3 # Timing overridable via env: ON_TIME=2 REST_TIME=1 ./run.sh PERIOD=1000000 # 1 kHz period in ns ON_TIME=${ON_TIME:-1} # seconds a color stays ON REST_TIME=${REST_TIME:-1} # seconds all OFF between colors LOOPS=${1:-3} RETRIES=50 # Channel mapping and polarity (verified on this board, all ACTIVE-HIGH): # Red -> 424f0000.pwm = pwmchip1 ch2 ON=duty PERIOD OFF=duty 0 # Green -> 424e0000.pwm = pwmchip0 ch0 ON=duty PERIOD OFF=duty 0 # Blue -> 424e0000.pwm = pwmchip0 ch2 ON=duty PERIOD OFF=duty 0 RED_CHIP=1; RED_CH=2 GRN_CHIP=0; GRN_CH=0 BLU_CHIP=0; BLU_CH=2 # write_retry FILE VALUE : write VALUE to FILE, retry on transient TPM busy/-ETIME, # and confirm the value took effect. Returns 0 on success. write_retry() { t=0 while [ "$t" -lt "$RETRIES" ]; do echo "$2" > "$1" 2>/dev/null [ "$(cat "$1" 2>/dev/null)" = "$2" ] && return 0 t=$((t+1)) done echo "WARN: could not write $2 to $1" >&2 return 1 } # init_pwm CHIP CH : export (fresh), set period BEFORE duty, start disabled with duty 0. # The i.MX TPM shares a counter between channels; a stale export with period=0 makes # later period writes fail with -EBUSY, so we unexport first for a clean state. init_pwm() { P="/sys/class/pwm/pwmchip${1}" [ -d "${P}/pwm${2}" ] && echo "$2" > "${P}/unexport" 2>/dev/null echo "$2" > "${P}/export" 2>/dev/null write_retry "${P}/pwm${2}/period" "$PERIOD" # period must be set before duty write_retry "${P}/pwm${2}/duty_cycle" 0 # start OFF echo 1 > "${P}/pwm${2}/enable" 2>/dev/null } set_duty() { # CHIP CH DUTY write_retry "/sys/class/pwm/pwmchip${1}/pwm${2}/duty_cycle" "$3" } led() { # CHIP CH STATE(on|off) -- all channels active-high if [ "$3" = on ]; then set_duty "$1" "$2" "$PERIOD"; else set_duty "$1" "$2" 0; fi } all_off() { led $RED_CHIP $RED_CH off led $GRN_CHIP $GRN_CH off led $BLU_CHIP $BLU_CH off } # Init: green and blue share pwmchip0, so init green first, then blue. init_pwm $RED_CHIP $RED_CH init_pwm $GRN_CHIP $GRN_CH init_pwm $BLU_CHIP $BLU_CH trap "all_off; echo; echo interrupted, all LEDs off; exit 0" INT TERM all_off echo "start: all OFF" n=0 while :; do c=$((n+1)) echo "[cycle $c] RED on"; led $RED_CHIP $RED_CH on; sleep "$ON_TIME" echo "[cycle $c] --- off"; all_off; sleep "$REST_TIME" echo "[cycle $c] GREEN on"; led $GRN_CHIP $GRN_CH on; sleep "$ON_TIME" echo "[cycle $c] --- off"; all_off; sleep "$REST_TIME" echo "[cycle $c] BLUE on"; led $BLU_CHIP $BLU_CH on; sleep "$ON_TIME" echo "[cycle $c] --- off"; all_off; sleep "$REST_TIME" n=$c [ "$LOOPS" -eq 0 ] && continue [ "$n" -ge "$LOOPS" ] && break done all_off echo "done ($n cycle(s)), all LEDs off"

Best Regards,
Zhiming

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user LED control on i.MX93 FRDM board

Re: user LED control on i.MX93 FRDM board