Question

我想用D编写的脚本打开和关闭嵌入式Linux板（BeagleBone Black）的led（字符设备）。

通过命令行，可以打开和关闭LED（例如，对于led＆＃34;用户LED D2 0和＃34;），使用：

cd /sys/class/leds/beaglebone:green:usr0
echo none > trigger
echo 1 > brightness
echo 0 > brightness

（echo none > trigger禁用默认＆＃34;心跳＆＃34;闪烁）

在第93页的D Cookbook中，我找到了有关如何通过C接口进行Linux系统调用的信息，如下所示：

void main(){
   import core.sys.posix.unistd;  // analogous to #include <unistd.h>
   string hello = "Hello, world!";
   write(1 /*stdout file descriptor*/, hello.ptr, hello.length);
}

这是访问角色设备的合适方式还是有更好的选择？

Answer 1

The unistd calls are indeed the correct way to do it. A character device in Linux is a special kind of file and is accessed the same way: you open it by path, then read or write to it, and close it when finished.

Note that open is actually inside core.sys.posix.fcntl, while read is in core.sys.posix.unistd.

You could also use std.file.write() from the D standard library to be a bit shorter. There's also chdir in there. So your shell example would literally become:

import std.file;
chdir("/sys/class/leds/beaglebone:green:usr0");
std.file.write("trigger", "none"); // write "filename", "data string"
std.file.write("brightness", "1");
std.file.write("brightness", "0");

You don't strictly have to use std.file.write as the full name with the import, I just like to since write is such a common word it clears up which one we mean.

Anyway, this function just wraps up the unistd calls for you: it opens, writes the string, and closes all in one (just like the shell echo!).

One small difference is shell echo sticks a \n at the end of the string. I didn't do that here. If the code doesn't work, try "1\n" and such instead, maybe the device requires that. But I doubt it.

But the std.file.write vs the core.sys.posix.unistd.write aren't that much different. The former is more convenient, the latter gives more precise control over it.

如何使用D访问linux角色设备？

1 个答案: