Android(Linux)控制GPIO的方法及实时性分析

　　Linux下控制GPIO的方法有N种，详细请参考《RPi GPIO Code Samples》，文中用十多种语言演示了如何控制GPIO，非常全面详尽。因此，这里不再多做赘述，仅把调试过程中整理的脚本贴上并做简单的分析。特别说明，Linux必须有root权限！！！否则会出现/system/bin/sh: can't create /sys/class/gpio/export: Permission denied等错误。

@echo off
echo adb root
adb root >%temp%\_tmp
@findstr "already" %temp%\_tmp
@if NOT errorlevel 1 goto config
timeout /T 10

:config
@echo on
adb shell chmod 0666 /sys/class/gpio/export
adb shell chmod 0666 /sys/class/gpio/unexport

adb shell echo 62 ">" /sys/class/gpio/export
adb shell echo 63 ">" /sys/class/gpio/export

adb shell chmod 0666 /sys/class/gpio/gpio62/direction
adb shell chmod 0666 /sys/class/gpio/gpio63/direction
adb shell chmod 0666 /sys/class/gpio/gpio62/value
adb shell chmod 0666 /sys/class/gpio/gpio63/value

adb shell echo out ">" /sys/class/gpio/gpio62/direction
adb shell echo out ">" /sys/class/gpio/gpio63/direction
adb shell echo 1 ">" /sys/class/gpio/gpio62/value
adb shell echo 1 ">" /sys/class/gpio/gpio63/value

@echo off
:top
adb shell echo 1 ">" /sys/class/gpio/gpio62/value
adb shell echo 1 ">" /sys/class/gpio/gpio63/value
rem @timeout /T 1
for /l %%i in (1,1,768) do echo %%i>nul
rem ping 0.0.0.1 -n 1 -w 500>nul
adb shell echo 0 ">" /sys/class/gpio/gpio62/value
adb shell echo 0 ">" /sys/class/gpio/gpio63/value
rem @timeout /T 1
for /l %%i in (1,1,768) do echo %%i>nul
rem ping 0.0.0.1 -n 1 -w 500>nul
goto top

pause.

　　该批处理文件运行在PC上，通过adb发送shell命令操作/sys/class/gpio以控制GPIO。

　　在MSM8996的开发板上测试，运行结果如下图所示。

　　从图中可以看出，两个GPIO的控制时间间隔相差约40ms，说明GPIO控制延时较为严重。　　

#!/system/bin/sh
chmod 0666 /sys/class/gpio/export
chmod 0666 /sys/class/gpio/unexport

echo 62 > /sys/class/gpio/export
echo 63 > /sys/class/gpio/export

chmod 0666 /sys/class/gpio/gpio62/direction
chmod 0666 /sys/class/gpio/gpio63/direction
chmod 0666 /sys/class/gpio/gpio62/value
chmod 0666 /sys/class/gpio/gpio63/value

echo out > /sys/class/gpio/gpio62/direction
echo out > /sys/class/gpio/gpio63/direction
echo 1 > /sys/class/gpio/gpio62/value
echo 1 > /sys/class/gpio/gpio63/value

while :
do
echo 1 > /sys/class/gpio/gpio62/value
echo 1 > /sys/class/gpio/gpio63/value
usleep 100000
echo 0 > /sys/class/gpio/gpio62/value
echo 0 > /sys/class/gpio/gpio63/value
usleep 100000
done

 　　该脚本运行在MSM8996开发板上，通过操作/sys/class/gpio以控制GPIO，执行结果如下图所示。

　　从图中可以看出，两个GPIO的控制时间间隔相差约0.6ms，说明GPIO控制延时较小。 

　  Android脚本文件可通过如下命令发送到开发板上，并修改其属性。 

pushd %~dp0
adb push .\gpio.sh /data/local/
adb shell chmod 777 /data/local/gpio.sh

 　　参考:

　　How to use GPIO signals(Linux应用程序控制GPIO) PNG
       https://developer.ridgerun.com/wiki/index.php/How_to_use_GPIO_signals

       树莓派上使用多种语言(C、Python、shell)控制GPIO
       http://elinux.org/RPi_GPIO_Code_Samples

       安卓应用程序通过JNI控制GPIO
       http://android.serverbox.ch/?p=972

　　Device Tree Usage

　　http://elinux.org/Device_Tree_Usage

　　BeagleBone Black (BBB) Pin Muxes

　　http://www.valvers.com/embedded-linux/beaglebone-black/step04-gpio

　　Beaglebone Pin Muxes

　　http://www.valvers.com/embedded-linux/beaglebone/step04-gpio1

　　Using Device Trees To Configure PRU IO Pins

　　http://www.ofitselfso.com/BeagleNotes/UsingDeviceTreesToConfigurePRUIOPins.php

　　BeagleBone Black GPIOs

　　http://kilobaser.com/blog/2014-07-15-beaglebone-black-gpios

　　gpio-header

　　https://github.com/nomel/beaglebone/tree/master/gpio-header

　　beaglebone-universal-io

　　https://github.com/cdsteinkuehler/beaglebone-universal-io