1 Hardware Overview
gpio interface,pin map:
AM335X_I2C0_W_C----------------------MCASP0_AXR1
/*4g-power*/
AM335X_MMC2_DAT0------------------GPMC_A1
/*4g-reset*/
AM335X_MMC2_DAT2------------------GPMC_A3
/*wifi-led*/
AM335X_WIFI------------------------------GPMC_A2
/*system-led*/
AM335X_XDMA_EVENT_INTR1------XDMA_EVENT_INTR1
/*key2 button*/
AM335X_SPI0_CS1-----------------------SPI0_CS1
2 GPIO DRIVER Overview
The gpio-leds driver provide userspace access gpio interface, for example: /sys/class/leds/4g-reset dir, under the dir have brightness、trigger, led trigger mode current triggers are:
"backlight" - LED will act as a back-light, controlled by the framebuffer system
"default-on" - LED will turn on (but for leds-gpio see "default-state"
property in Documentation/devicetree/bindings/gpio/led.txt)
"heartbeat" - LED "double" flashes at a load average based rate
"disk-activity" - LED indicates disk activity
"ide-disk" - LED indicates IDE disk activity (deprecated),in new implementations use "disk-activity"
"timer" - LED flashes at a fixed, configurable rate
The gpio driver can be used to pullup/pulldown led(io) from the User interface as shown by the below diagram..
3 Kernel GPIO porting
PIN MUX
user_leds_s0: user_leds_s0 {
pinctrl-single,pins = <
AM33XX_IOPAD(0x9a8, PIN_OUTPUT_PULLUP | MUX_MODE7) /* mcasp0_axr1.gpio3_20 ----> eeprom_write_control*/
AM33XX_IOPAD(0x844, PIN_OUTPUT_PULLUP | MUX_MODE7) /* gpmc_a1.gpio1_17 ----> 4g-power*/
AM33XX_IOPAD(0x84c, PIN_OUTPUT_PULLUP | MUX_MODE7) /* gpmc_a3.gpio1_19 ---->4g-reset*/
AM33XX_IOPAD(0x848, PIN_OUTPUT_PULLUP | MUX_MODE7) /* gpmc_a2.gpio1_18 ---->wifi-led*/
AM33XX_IOPAD(0x9b4, PIN_OUTPUT_PULLUP | MUX_MODE7) /* xdma_event_intr1.gpio0_20 ---->system-led*/
AM33XX_IOPAD(0x960, PIN_INPUT_PULLUP | MUX_MODE7) /* spi0_cs1.gpio0_6 ----> button */
>;
};
GPIO DTS NODE
leds {
pinctrl-names = "default";
pinctrl-0 = <&user_leds_s0>;
compatible = "gpio-leds";
led1 {
label = "heartbeat";
gpios = <&gpio0 20 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "heartbeat";
};
led2 {
label = "eeprom-write-control";
gpios = <&gpio3 20 GPIO_ACTIVE_HIGH>;
default-state = "off";
};
led3 {
label = "4g-power";
gpios = <&gpio1 17 GPIO_ACTIVE_HIGH>;
default-state = "on";
};
led4 {
label = "4g-reset";
gpios = <&gpio1 19 GPIO_ACTIVE_HIGH>;
default-state = "off";
};
led5 {
label = "wif-led";
gpios = <&gpio1 18 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "heartbeat";
default-state = "off";
};
};
4 User Space Interface
root@am335x-evm:/sys/class/leds/4g-reset# ls
brightness device max_brightness power subsystem trigger uevent