Analog Output - PWM/GPT

The RZ/G3E CPU supports 16 GPT (General PWM Timer) which can be used for PWM output. However, only one is available on the SOM Carrier Board.

SOM Carrier Board pin name	Available on	Pwm	GPT	DTS
BL_CONTRAST_PWM-GPIO	JP45 pin 1	pwm0	GPT1, GTIOC12A	gpt1_4 channel A

The PWM is available on pin BL_CONTRAST_PWM-GPIO which is used for backlight for LVDS0/1.

The rzg3e-ea-som-hdmi.dtb file has been configured to use that pin as a pwm0 instead. It can be accessed on JP45 pin 1:

The GPT peripheral has a lot of different possible use cases (described in r01us0484ej0110-rz_GPT_UME.pdf dowloadable from RZ/G3E Board Support Package). Here we will only show the basic PWM functionallity.

U-Boot

Not currently available.

Linux

To see which PWM channels have been enabled in the device tree.

ls /sys/class/pwm/

pwmchip0

Each PWM channel has its own pwmchipX folder with a couple of interesting files.

ls /sys/class/pwm/pwmchip0/

device     export  npwm      power
subsystem  uevent  unexport

To use a pwm channel it must first be exported.

echo 0 > /sys/class/pwm/pwmchip0/export

It will then appear as a pwm0 node. For echo 1 it would have been pwm1 and so on.

ls /sys/class/pwm/pwmchip0/pwm0

capture   duty_cycle   enable   period
polarity  power        uevent

To set the PWM frequency to 100 kHz (100kHz equals 10000 ns period time) and set the duty cycle to 70% (0.7 * period time equals 7000).

cd /sys/class/pwm/pwmchip0/pwm0
echo 10000 > period
echo 7000 > duty_cycle
echo 1 > enable

This signal can then be observed either with an oscilloscope or by measuring with a multimeter that will typically measure an average voltage. In this case the average should be ca 2.3V which is 70% of 3.3V.