GPIO更改状态时，如何更新sysfs? [英] How is sysfs updated when a GPIO changes state?

问题描述

假定可以在sysfs中将gpio X导出为输入引脚，然后在/sys/class/gpio/中创建一个名为gpioX的目录. gpioX/包含少量文件，例如"value"，它们代表gpio X的当前状态(高或低).

Assume that the gpio X can be exported in sysfs as an input pin, after doing that a directory called gpioX will be created into /sys/class/gpio/. gpioX/ contains few file such as "value" which represents the current state of the gpio X (high or low).

当施加到引脚X的信号改变其状态(例如，从低到高)时，会发生什么(在内核空间中)?

What happens (in kernel space) when the signal applied to the pin X changes its state (for example from low to high)?

我的意思是，在转换前gpioX/value包含"low"，但之后它将包含"high"值.操作系统如何更新此文件?

I mean, before the transition gpioX/value contains "low", but after that it will contain "high" value. How is this file updated by the OS?

我认为需要一个中断机制.它是否使用中断机制来更新sysfs?

I think that an interrupt mechanism is required.Does it use an interrupt mechanism to update sysfs?

推荐答案

操作系统如何更新此文件?我认为需要一种中断机制.

How is this file updated by the OS? I think that an interrupt mechanism is required.

除非支持轮询，否则不需要中断机制( man poll )或备用的异步通知.至少在大多数版本中，/sys/class/gpio/仅在有人读取文件时才读取GPIO级别.

It does not require an interrupt mechanism unless it supports polling (man poll) or alternate asynchronous notifications. At least with most version, the /sys/class/gpio/ only does a read of the GPIO level when someone reads the file.

sysfs ， debugfs ， configfs ， procfs 等是虚拟文件系统.当您访问文件时，Linux内核中的代码将运行以提供该值. sysfs 仅提供类似于接口的文件；这并不表示它已得到支持的实际状态.状态是可以随时读取的GPIO级别.

sysfs, debugfs, configfs, procfs, etc are virtual file systems. When you access the file, code within the Linux kernel runs to provide the value. sysfs only provides a file like interface; that doesn't mean it is backed with actual state. The state is the GPIO level which can be read at any time.

gpio .txt 获取更多信息(尤其是您的特定Linux版本).

gpio_value_show() appears to be the current implementation. What you describe with interrupts is possible. It can be done through the sysfs_set_active_low() function or the sysfs file /sys/class/gpio/gpioN/edge. Writing to the file may return an error if the GPIO doesn't support interrupts. See gpio.txt for more (especially for your particular version of Linux).

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