TIM Linux driver

1 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.

2 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.

3 Configuration

3.1 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

3.2 Device tree

Refer to the TIM device tree configuration article when configuring the TIM 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 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

6 Source code location

The TIM Linux driver source code is composed of:

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

Multifunction device

Direct Memory Access

Pulse Width Modulation

Industrial I/O Linux subsystem

Analog-to-digital converter. The process of converting a sampled analog signal to a digital code that represents the amplitude of the original signal sample.

Digital-to-analog converter (Electronic circuit that converts a binary number into a continuously varying value.)

Digital Filter for Sigma-Delta Modulator

Register map (Linux registers map abstraction API)

Debug File System (See https://en.wikipedia.org/wiki/Debugfs for more details)

Multifunction device

Direct Memory Access

Pulse Width Modulation

Industrial I/O Linux subsystem

Analog-to-digital converter. The process of converting a sampled analog signal to a digital code that represents the amplitude of the original signal sample.

Digital-to-analog converter (Electronic circuit that converts a binary number into a continuously varying value.)

Digital Filter for Sigma-Delta Modulator

Register map (Linux registers map abstraction API)

Debug File System (See https://en.wikipedia.org/wiki/Debugfs for more details)

Application programming interface