TIM Linux driver

Article purpose

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

• Which TIM 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.

Short description

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

MFD driver:

• handles registers, clock and DMA resources
• detects the TIM counter resolution, e.g. 16 or 32 bits.

PWM driver:

• detects the number of TIM channels.
• handles PWM output channels.
• handles PWM capture channels (input). Note that the PWM capture relies on DMA, which is handled by the MFD core.

IIO driver:

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

Configuration

Kernel configuration

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

Enable the following configurations (and their dependencies):

• CONFIG_MFD_STM32_TIMERS
• CONFIG_PWM_STM32
• CONFIG_IIO_STM32_TIMER_TRIGGER

Device Drivers  --->
  -> Multifunction device drivers  --->
     <*> Support for STM32 Timers
  -> Pulse-width modulation (PWM) support  --->
     <*> STMicroelectronics STM32 PWM
  -> Industrial I/O support  --->
     -> Triggers - standalone  --->
        <*> STM32 timer trigger

Device tree

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

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

How to trace and debug

The TIM Linux driver can access the timer registers through REGMAP.

It comes with debugfs entries, which allow dumping registers:

$ cd /sys/kernel/debug/regmap
$ ls
40004000.timer  44000000.timer

$ cd 44000000.timer
$ cat registers
000: 00000081
004: 00000000
008: 00000000
00c: 00000000
...

It also comes with tracepoints:

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

Source code location

The TIM Linux driver source code is composed of:

• drivers/mfd/stm32-timers.c | |}} stm32-timers.c MFD driver to handle common resources: registers, clock, dmas.
• drivers/pwm/pwm-stm32.c | |}} pwm-stm32.c PWM driver to handle PWM channel(s).
• drivers/iio/trigger/stm32-timer-trigger.c | |}} stm32-timer-trigger.c IIO driver to handle trigger source for other internal peripherals and quadrature encoder interface.
• include/linux/mfd/stm32-timers.h| |}} include/linux/mfd/stm32-timers.h and include/linux/iio/timer/stm32-timer-trigger.h| |}} include/linux/iio/timer/stm32-timer-trigger.h header files

References

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