From Manuals

Contents 1 Examples using Python 1.1 Blinky Example 1.2 Button Example 1.3 GPIO Example

Examples using Python

The following application note covers the use of Electrum100's peripherals using Python. SYSFS method is used to access the GPIO's. To create the interfaces for GPIO's under /sys/class/gpio/*, the following configuration has to be enabled in the board configuration file

CONFIG_GPIO_SYSFS=y

Blinky Example

User LED is connected to GPIO PA30. An interface for the user LED is created in the kernel by adding the following code in board-electrum-100.c

/*
 * LEDs
 */
static struct gpio_led ek_leds[] = {
	{	/* led1, yellow */
		.name			= "ds1",
		.gpio			= AT91_PIN_PA25,
		.default_trigger	= "heartbeat",
	},
	{	/* led2, green */
		.name			= "ds2",
		.gpio			= AT91_PIN_PA30,
		//.active_low		= 1,
		.default_trigger	= "none",
	}
};

And add the following lines in ek_board_init()

/* LEDs */
	at91_gpio_leds(ek_leds, ARRAY_SIZE(ek_leds));

Python script for Blinky Example:

import sys
import time

print "Blinking User LED"
print "Enter CTRL+C to exit"

def ledon():
        value = open("/sys/class/leds/ds2/brightness","w")
        value.write(str(1))
        value.close()

def ledoff():
        value = open("/sys/class/leds/ds2/brightness","w")
        value.write(str(0))
        value.close()

while True:
        ledon()
        time.sleep(.5)
        ledoff()
        time.sleep(.5)

Button Example

In Electrum100, GPIO PA31 is used for the User Button.

import sys
import time

print "Button Example"
print "Press CTRL + C to exit"

def pins_export():
        try:
                pin1export = open("/sys/class/gpio/export","w")
                pin1export.write(str(63))
                pin1export.close()
        except IOError:
                print "INFO: GPIO 63 already Exists, skipping export gpio"

def read_button():
        fp1 = open("/sys/class/gpio/gpio63/value","r")
        value = fp1.read()
        return value
        fp1.close()

def write_led(value):
        fp2 =  open("/sys/class/leds/ds2/brightness","w")
        fp2.write(str(value))
        fp2.close()

pins_export()
while True:
        button_value =  read_button()
        write_led(button_value)

GPIO Example

The following example, allows the user to set any selected GPIO pin as either Input and Output and reads the values from all the ports configured. As some of the GPIO's have alternate Functions, it is required that, pins have to be initialized as GPIO's before executing the following test example. set-gpio is a C-binary that initializes a single pin at a time. (Default as Input Pin)

import sys
import time
import re

def setpins(pin_no, pin_direction):
        gpioopnum = "gpio%s" % (str(pin_no), )
         pin1dir = open("/sys/class/gpio/"+gpioopnum+"/direction","w")
        if pin_direction == 1:
                pin1dir.write("high")
        else:
                pin1dir.write("in")
        pin1dir.close()

def readpins(pin_no):
        gpioopnum = "gpio%s" % (str(pin_no), )
        pin1val = open("/sys/class/gpio/"+gpioopnum+"/value","r")
        output = pin1val.read()
        print "The value on the PIN %s is : %s" % (str(pin_no), str(output))
        pin1val.close()

def unexport_pins(pins):
        try:
                fp4 = open("/sys/class/gpio/unexport","w")
 fp4.write(str(pins))
                fp4.close()
        except IOError:
                print "GPIO %s is not found, so skipping unexport gpio" % (str(pins), )

def export_pins(pins):
        try:
                fp1 = open("/sys/class/gpio/export","w")
                fp1.write(str(pins))
                fp1.close()
        except IOError:
                print "GPIO %s already Exists, so skipping export gpio" % (str(pins), )

print "Warning: Make sure that the script to enable GPIO ports is executed prior to this. The script may not work as intended if the Ports are not initialized properly"+"\n"
for i in range(1 , len(sys.argv)):
        export_pins(sys.argv[i])
 direction = raw_input(" Configure PIN %s as OUTPUT(1) / INPUT(2) ?: " % (str(sys.argv[i]), ))
        setpins(sys.argv[i], int(direction))

print "\n"+"            Reading PIN values....."
for i in range(1 , len(sys.argv)):
        readpins(sys.argv[i])

for i in range(1 , len(sys.argv) ):
        unexport_pins(sys.argv[i])