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我正在尝试监视GPIO引脚,根据Linux文档,我应该能够通过使用select监视/ sys / class / gpio / gpio ## / value文件来完成此操作：
"value" ... reads as either 0 (low) or 1 (high). If the GPIO
is configured as an output,this value may be written;
any nonzero value is treated as high.
If the pin can be configured as interrupt-generating interrupt
and if it has been configured to generate interrupts (see the
description of "edge"),you can poll(2) on that file and
poll(2) will return whenever the interrupt was triggered. If
you use poll(2),set the events POLLPRI and POLLERR. If you
use select(2),set the file descriptor in exceptfds. After
poll(2) returns,either lseek(2) to the beginning of the sysfs
file and read the new value or close the file and re-open it
我试图在Ruby中执行此操作,并且根据IO.Select documentation调用select(2).
所以,凭借这些知识,我将以下测试程序汇集在一起：
fd = File.open("/sys/class/gpio/gpio17/value","r")
loop do
rs,ws,es = IO.select(nil,nil,[fd],5)
if es
r = es[0]
puts r.read(1)
else
puts "timeout"
end
end
但是,它没有检测到任何引脚变化.当我启动这个应用程序时,它将立即进入if块并显示引脚的当前值,然后每5秒打印一次超时.
我读错了文档吗？不应该选择能够监控吗？
最佳答案
在选择将在GPIO引脚上正确触发之前,您需要设置引脚的边沿触发.从the GPIO docs开始：
"edge" ... reads as either "none","rising","falling",or
"both". Write these strings to select the signal edge(s)
that will make poll(2) on the "value" file return.
This file exists only if the pin can be configured as an
interrupt generating input pin.
在Ruby中简单地说：
File.open("/sys/class/gpio/gpio17/edge","w") { |f| f.write("both") }
上面的完整示例如下所示：
fd = File.open("/sys/class/gpio/gpio17/value","r")
File.open("/sys/class/gpio/gpio17/edge","w") { |f| f.write("both") }
loop do
rs,5)
if es
r = es[0]
puts r.read(1)
else
puts "timeout"
end
end
（编辑：安卓应用网）
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