Last edited 2 months ago

LPTIM Linux driver

Applicable for STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

1. Article purpose[edit source]

This article introduces the LPTIM Linux® driver for the LPTIM internal peripheral[1]:

  • 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[edit source]

The LPTIM[1] 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[2], DAC[3], DFSDM[4]

Counter driver:

  • handles the quadrature encoder interface[5] as well as the external event counter.

3. Configuration[edit source]

3.1. Kernel configuration[edit source]

Activate the LPTIM[1] 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):

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[edit source]

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

4. How to use[edit source]

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[edit source]

The LPTIM Linux driver can access LPTIM registers through REGMAP.

It comes with debugfs[6] 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[7]:

$ cd /sys/kernel/debug/tracing
$ cat available_events | grep regmap

6. Source code location[edit source]

The LPTIM Linux driver is composed of:

7. References[edit source]