Linux/AM3352: PWM driver in U-boot

Ankur Tank

Expert 2985 points

Part Number: AM3352

Tool/software: Linux

We are using Beaglbone black based custom board. We have LEDs connected on the PWM lines.

We are updating our U-Boot from version 2013 to 2017.01. In general there is PWM driver support in U-Boot.

Why pwm driver is not available for am335x in U-Boot code ? Is there a specific reason for same ?

Any future plans for adding pwm driver in U-Boot ?

Thanks,

Regards,

Ankur

over 6 years ago

0 Pavel Botev over 6 years ago

TI__Guru**** 170625 points

Hi Ankur,

I see we have Timer driver in u-boot, and AM335x Timer module can be used for PWM:

u-boot-2017.01/arch/arm/dts/am33xx.dtsi

u-boot-2017.01/drivers/timer/omap-timer.c

Also I see AM335x eCAP module is used in PWM mode for AM335x EVM and SK boards:

u-boot-2017.01/arch/arm/dts/am335x-evm.dts
u-boot-2017.01/arch/arm/dts/am335x-evmsk.dts

u-boot-2017.01/drivers/video/pwm_backlight.c

&epwmss2 {
status = "okay";

ecap2: ecap@48304100 {
status = "okay";
pinctrl-names = "default";
pinctrl-0 = <&ecap2_pins>;
};
};

backlight {
compatible = "pwm-backlight";
pwms = <&ecap2 0 50000 PWM_POLARITY_INVERTED>;
brightness-levels = <0 58 61 66 75 90 125 170 255>;
default-brightness-level = <8>;
};

ecap2_pins: backlight_pins {
pinctrl-single,pins = <
AM33XX_IOPAD(0x99c, MUX_MODE4) /* mcasp0_ahclkr.ecap2_in_pwm2_out */
>;
};

Regards,
Pavel

0 Pavel Botev over 6 years ago in reply to Pavel Botev

TI__Guru**** 170625 points

You can also explore how pxm2 AM335x board is using eCAP module for PWM:

u-boot-2017.01/arch/arm/include/asm/arch-am33xx/cpu.h
u-boot-2017.01/board/siemens/pxm2/board.c

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Linux/AM3352: PWM driver in U-boot