LPTIM Linux driver

Applicable for

STM32MP13x lines, STM32MP15x lines

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1 Article purpose

This article introduces the LPTIM Linux^® driver for the LPTIM internal peripheral:

• Which LPTIM features are supported by the driver
• How to configure, use and debug the driver
• What is the driver structure, and where the source code can be found.

2 Short description

The LPTIM Linux driver (kernel space) is based on the PWM, IIO and counter frameworks. It provides several functionalities:

MFD driver:

• handles common resources (registers, clock)

PWM driver:

• handles the PWM output channel (single channel)

IIO hardware trigger driver:

• handles hardware trigger sources (synchronously with PWM) for other internal peripherals such as ADC, DAC, DFSDM

Counter driver:

• handles the quadrature encoder interface as well as the external event counter.

3 Configuration

3.1 Kernel configuration

Activate the LPTIM Linux driver in the kernel configuration using the Linux Menuconfig tool: Menuconfig or how to configure kernel.

Enable the following configurations (as well as their dependencies):

• CONFIG_MFD_STM32_LPTIMER
• CONFIG_PWM_STM32_LP
• CONFIG_IIO_STM32_LPTIMER_TRIGGER
• CONFIG_STM32_LPTIMER_CNT

Device Drivers  --->
   -> Multifunction device drivers  --->
      <*> Support for STM32 Low-Power Timer
   -> Pulse-width modulation (PWM) support  --->
      <*> STMicroelectronics STM32 PWM LP
   -> Industrial I/O support  --->
      -> Triggers - standalone  --->
         <*> STM32 Low-Power Timer Trigger
   -> Counter support  --->
      <*> STM32 LP Timer encoder counter driver

3.2 Device tree

Refer to the LPTIM device tree configuration article when configuring the LPTIM Linux kernel driver.

4 How to use

How to use PWM with sysfs interface

How to set up a TIM or LPTIM trigger using the sysfs interface

How to use the quadrature encoder with the sysfs interface

5 How to trace and debug

The LPTIM Linux driver can access LPTIM registers through REGMAP.

It comes with debugfs entries, which allow dumping registers:

$ cd /sys/kernel/debug/regmap
$ ls
40004000.timer  40009000.timer

$ cd 40009000.timer
$ cat registers
000: 00000003
004: 00000000
008: 00000000
...

It also comes with tracepoints:

$ cd /sys/kernel/debug/tracing
$ cat available_events | grep regmap
...
regmap:regmap_reg_read
regmap:regmap_reg_write

6 Source code location

The LPTIM Linux driver is composed of:

• stm32-lptimer.c driver to handle common resources, such as registers and clock.
• pwm-stm32-lp.c driver to handle PWM channel
• stm32-lptimer-trigger.c driver to handle trigger sources for other internal peripherals
• stm32-lptimer-cnt.c driver to handle quadrature encoder and external event counter
• include/linux/mfd/stm32-lptimer.h and include/linux/iio/timer/stm32-lptim-trigger.h header files