这两天遇到个奇怪的问题，手机电量低于15%的时候，只会弹出低电量的提示框，低电量指示灯并没有闪烁。
查看log
01-01 00:02:36.294016 1253 1286 D lights : set_led_state colorRGB=FFFF0000, onMS=125, offMS=2875
01-01 00:02:36.294087 1253 1286 D lights : blink_red, level=255, onMS=125, offMS=2875
01-01 00:02:36.294147 1253 1286 D lights : write timer to /sys/class/leds/red/trigger
01-01 00:02:36.295306 1253 1286 D lights : write_str open fd=149
01-01 00:02:36.306318 1253 1286 D lights : write timer to /sys/class/leds/red/trigger amt = 5
01-01 00:02:36.308148 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.313706 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.319396 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.324970 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.330605 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.336586 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.342146 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.348308 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.353941 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.359572 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!!
01-01 00:02:36.365457 1253 1286 D lights : RED_DELAY_OFF_FILE doesn't exist or cannot write!! i=10
01-01 00:02:36.365742 1253 1286 D lights : write_int open fd=-1
01-01 00:02:36.366032 1253 1286 D lights : write_int open fd=-1可以看到是因为write_str(RED_TRIGGER_FILE, “timer”); 之后，并没有生成delay_on和delay_off两个文件。
手动用echo测试
先echo timer >> /sys/class/leds/red/trigger 测试，可以生成 delay_on和delay_off两个文件，然后
echo 200 >> /sys/class/leds/red/delay_off
echo 200 >> /sys/class/leds/red/delay_on 这样设置一下时间，指示灯就可以闪烁。
write_int open fd=-1 返回-1 ，意味着没有权限，这两个文件是动态注册权限的，所以看ueventd.mt6735.rc文件，找到下面两句
/sys/devices/platform/leds-mt65xx/leds/red delay_on 0664 system system
/sys/devices/platform/leds-mt65xx/leds/red delay_off 0664 system system通过adb连接设备，发现leds-mt65xx的路径不对，实际上在
/sys/devices/leds-mt65xx，尝试修改上面两句为
/sys/devices/leds-mt65xx/leds/red delay_on 0664 system system
/sys/devices/leds-mt65xx/leds/red delay_off 0664 system system重新编译下载，问题解决。