LPTIM Linux driver
目录
Article purpose
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.
Short description
The LPTIM[1] Linux driver (kernel space) is based on the PWM and IIO 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]
IIO counter driver:
- handles the quadrature encoder interface[5] as well as the external event counter.
Configuration
Kernel configuration
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):
- 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
-> Counters --->
<*> STM32 low-power timer encoder counter driver
Device tree
Refer to the LPTIM device tree configuration article when configuring the LPTIM 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 trace and debug
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 ... regmap:regmap_reg_read regmap:regmap_reg_write
Source code location
The LPTIM Linux driver is composed of:
- drivers/mfd/stm32-lptimer.c | |}} stm32-lptimer.c driver to handle common resources, such as registers and clock.
- drivers/pwm/pwm-stm32-lp.c | |}} pwm-stm32-lp.c driver to handle PWM channel
- drivers/iio/trigger/stm32-lptimer-trigger.c | |}} stm32-lptimer-trigger.c driver to handle trigger sources for other internal peripherals
- drivers/iio/counter/stm32-lptimer-cnt.c | |}} stm32-lptimer-cnt.c driver to handle quadrature encoder and external event counter
- include/linux/mfd/stm32-lptimer.h| |}} include/linux/mfd/stm32-lptimer.h and include/linux/iio/timer/stm32-lptim-trigger.h| |}} include/linux/iio/timer/stm32-lptim-trigger.h header files
References
<securetransclude src="ProtectedTemplate:PublicationRequestId" params="9230 | 2018-10-16 | AnneJ"></securetransclude> <securetransclude src="ProtectedTemplate:ArticleBasedOnModel" params="Linux driver article model"></securetransclude>
