Blinky, Button & GPIO examples using Python
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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 read the values from all the pins 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])
Procedure:
electrum100:/home/python# set-gpio 32 PIOA 0 set as Input electrum100:/home/python# set-gpio 55 PIOA 23 set as Input
Before Connecting the Short cable between PA0 and PA23
electrum100:/home/python# python gpio1.py 32 55
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
Configure PIN 32 as OUTPUT(1) / INPUT(2) ?: 1
Configure PIN 55 as OUTPUT(1) / INPUT(2) ?: 2
Reading PIN values.....
The value on the PIN 32 is : 1
The value on the PIN 55 is : 0
After connecting the Short cable between PA0 and PA23
electrum100:/home/python# python gpio1.py 32 55
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
Configure PIN 32 as OUTPUT(1) / INPUT(2) ?: 1
Configure PIN 55 as OUTPUT(1) / INPUT(2) ?: 2
Reading PIN values.....
The value on the PIN 32 is : 1
The value on the PIN 55 is : 1
The convention used to represent the Pin numbers using SYSFS procedure is explained with examples.
PA Base - 32
PB Base - 64
PC Base - 96
Ex: To intialize PA1, use PA-Base + 1 = 32 + 1 = 33
PA31, use 32 + 31 = 63
PB0, use PB-Base + 0 = 64 + 0 = 64
PC10, use 96 + 10 = 106