I.MX6 PWM: Difference between revisions

From embeddedTS Manuals
(Created page with "The PWM controller is accessed through the Linux driver. This will require modifying the kernel or device tree. See the #Compile the Kernel section to get a build enviro...")
 
m (Links auto-updated for 2022 re-branding ( https://github.com/embeddedarm/linux-3.10.17-imx6/blob/imx_4.1.15_1.0.0_ga/arch/arm/boot/dts/imx6qdl-ts4900-ts8390.dtsi#L256 →‎ https://github.com/embeddedTS/linux-3.10.17-imx6/blob/imx_4.1.15_1.0.0_ga/arch/arm/boot/dts/imx6qdl-ts4900-ts8390.dtsi#L256))
 
(2 intermediate revisions by one other user not shown)
Line 1: Line 1:
The PWM controller is accessed through the Linux driver.  This will require modifying the kernel or device tree.  See the [[#Compile the Kernel]] section to get a build environment working.  You will then need to modify either a baseboard specific device tree, or the fallback arch/arm/boot/dts/imx6qdl-ts4900.dtsi.  This example will assume the latter.
The PWM controller is accessed through the Linux driver.  PWM is available on these pins:
* CN1_19 (channel 1) (LCD Data 8)
* CN1_21 (channel 2) (LCD Data 9)
* CN2_74 (channel 2) (replaces USB_OTG_ID)
* CN1_57 (channel 3)


In this case this is the PWM on the TS-4900 on CN1_57.  First the pin must be configured to be PWM and not a GPIO.  Add the pinctrl_pwm3 after the imx-ts4900 {:
This will require modifying the kernel or device tree to set up these pins as PWM.  See the [[#Compile the Kernel]] section to get a build environment working.  You will then need to modify either a baseboard specific device tree, or the fallback arch/arm/boot/dts/imx6qdl-ts4900.dtsi.  This example will assume the latter.
 
In this case this is the example PWM channel 3 on the TS-4900 on CN1_57.  First the pin must be configured to be PWM and not a GPIO.  Add the pinctrl_pwm3 after the imx-ts4900 {:
<source lang=javascript>
<source lang=javascript>
iomuxc {
iomuxc {
Line 14: Line 20:
};
};
</source>
</source>
The MX6QDL_PAD_SD4_DAT1__PWM3_OUT pad name comes from imx6q-pinfunc.h (or imx6dl-pinfunc.h).  The format follows MX6QDL_PAD_<CPU Pad Name>__<Function of that pad>.  This specifies SD4_DAT1  to be used as PWM3's output.


At the end of the file enable the PWM controller, and point at this pinctrl:
At the end of the file enable the PWM controller, and point at this pinctrl:
Line 23: Line 31:
};
};
</source>
</source>
 
This will attach a driver to actually drive that pin that is now configured for PWM.  After rebuilding and installing this device tree you will now have a directory "/sys/class/pwm/pwmchip0".  This can be used to control the PWM.
After rebuilding and installing this device tree you will now have a directory "/sys/class/pwm/pwmchip0".  This can be used to control the PWM.
<source lang=bash>
<source lang=bash>
# Each PWM controller has "1" pwm which will be pwm channel 0
# Each PWM controller has "1" pwm which will be pwm channel 0
Line 54: Line 61:
</source>
</source>


A common use of the PWM is for backlight control which is specified in the device tree.  Our TS-TPC-8390 [https://github.com/embeddedarm/linux-3.10.17-imx6/blob/imx_4.1.15_1.0.0_ga/arch/arm/boot/dts/imx6qdl-ts4900-ts8390.dtsi#L256 baseboard device tree] can be used as an example.
A common use of the PWM is for backlight control which is specified in the device tree.  Our TS-TPC-8390 [https://github.com/embeddedTS/linux-3.10.17-imx6/blob/imx_4.1.15_1.0.0_ga/arch/arm/boot/dts/imx6qdl-ts4900-ts8390.dtsi#L256 baseboard device tree] can be used as an example.


In addition to setting up the PWM as demonstrated above, the PWM is connected to the pwm-backlight driver.
In addition to setting up the PWM as demonstrated above, the PWM is connected to the pwm-backlight driver.
Line 66: Line 73:
};
};
</source>
</source>
This specifies PWM3 to run at 5MHz with duty cycles specified in brightness-levels up to 255.  This example creates 8 levels of brightness for the backlight, but more duty cycles can be added if more levels are needed.
This specifies PWM3 to run with 5000000 ns periods (200hz) with duty cycles specified in brightness-levels up to 255.  This example creates 8 levels of brightness for the backlight, but more duty cycles can be added if more levels are needed.

Latest revision as of 16:34, 17 January 2022

The PWM controller is accessed through the Linux driver. PWM is available on these pins:

  • CN1_19 (channel 1) (LCD Data 8)
  • CN1_21 (channel 2) (LCD Data 9)
  • CN2_74 (channel 2) (replaces USB_OTG_ID)
  • CN1_57 (channel 3)

This will require modifying the kernel or device tree to set up these pins as PWM. See the #Compile the Kernel section to get a build environment working. You will then need to modify either a baseboard specific device tree, or the fallback arch/arm/boot/dts/imx6qdl-ts4900.dtsi. This example will assume the latter.

In this case this is the example PWM channel 3 on the TS-4900 on CN1_57. First the pin must be configured to be PWM and not a GPIO. Add the pinctrl_pwm3 after the imx-ts4900 {: 

iomuxc {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_hog>;

	imx6-ts4900 {
		pinctrl_pwm3: pwm3grp {
			fsl,pins = <
				MX6QDL_PAD_SD4_DAT1__PWM3_OUT		0x1b088
			>;
		};

The MX6QDL_PAD_SD4_DAT1__PWM3_OUT pad name comes from imx6q-pinfunc.h (or imx6dl-pinfunc.h). The format follows MX6QDL_PAD_<CPU Pad Name>__<Function of that pad>. This specifies SD4_DAT1 to be used as PWM3's output.

At the end of the file enable the PWM controller, and point at this pinctrl: 

&pwm3 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_pwm3>;
	status = "okay";
};

This will attach a driver to actually drive that pin that is now configured for PWM. After rebuilding and installing this device tree you will now have a directory "/sys/class/pwm/pwmchip0". This can be used to control the PWM. 

# Each PWM controller has "1" pwm which will be pwm channel 0
echo 0 > /sys/class/pwm/pwmchip0/export

This will create a pwm0 directory under pwmchip0 which has these files:

period Total period, inactive and active time in the PWM cycle specified in nanoseconds.
duty_cycle Active time of the PWM signal specified in nanoseconds. Must be less than the period.
enable Write 1 to enable, 0 to disable
polarity When the pwm is disabled this can be written as "normal" for default behavior or "inversed" to invert the signal.

As an example, this will set a 50khz signal with 50 percent duty cycle. 

# 20us is the period for 50khz
echo 20000 > /sys/class/pwm/pwmchip0/pwm0/period
echo 10000 > /sys/class/pwm/pwmchip0/pwm0/duty_cycle
echo 1 > /sys/class/pwm/pwmchip0/pwm0/enable

A common use of the PWM is for backlight control which is specified in the device tree. Our TS-TPC-8390 baseboard device tree can be used as an example.

In addition to setting up the PWM as demonstrated above, the PWM is connected to the pwm-backlight driver. 

	backlight_lcd {
		compatible = "pwm-backlight";
		pwms = <&pwm3 0 5000000>;
		brightness-levels = <0 128 140 160 180 200 220 240 255>;
		default-brightness-level = <8>;
		power-supply = <&reg_3p3v>;
	};

This specifies PWM3 to run with 5000000 ns periods (200hz) with duty cycles specified in brightness-levels up to 255. This example creates 8 levels of brightness for the backlight, but more duty cycles can be added if more levels are needed.

Retrieved from "http://docs.embeddedTS.com/index.php?title=I.MX6_PWM&oldid=14680"