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Alternate User Interfaces
CS423
Dick Steflik
User Interfaces
Traditional User Interfaces for Devices
Allow the user control of/over the internal state of
the device
Buttons/Keys
Lamps, LEDs, LCD panels
Knobs, sliders
On devices with embedded microcontrollers this
can also be done via a web based user
Interface (web page)
Common Gateway Interface
A specification that describes how a web server
exchanges data with a web program
How data from a web form is sent to a web
server
What the web server does with the data
How the web server activates a specific
program
How the program gets the user data and how it
responds
http://hoohoo.ncsa.uiuc.edu/cgi/
CGI
Standard HTTP used
can use GET or POST methods to send data
GET sends data (as name/value pairs) attached to URL
POST send data (as name/value pairs) in the HTTP body
Server will receive the request packet and place the data in an
environment variable called QUERYSTRING and place it in
SYSIN so that it can be retrieved by the processing program
SYSOUT is connected to the outgoing socket of the web server
so that whatever is sent to sysout will go back as the body of
the response packet (this could be a subsequent web page or
just a positive response)
Pictorially
Request Packet
SYSIN
Web Server
Browser
Response Packet
SYSOUT
C Program
cgipio.c
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define BUFFERSIZE 257
#define LED_OFFSET 19
int main(int argc, char *argv[])
{
int i = 0;
int pio = 0;
int retval = 0;
int toggle = 0;
int led_on = -1;
int read_bytes = 0;
unsigned int pio_buffer;
char buffer[BUFFERSIZE];
/* Read in stuff from stdinn */
while ((i = read(0, buffer, BUFFERSIZE-1)) != 0) {
read_bytes += i;
}
buffer[read_bytes] = '\0';
if(strstr(buffer, "toggle=1") != 0) {
toggle = 1;
}
(cont.)
/* Print basic headers */
printf("HTTP/1.0 200 OK\n");
printf("Content-type: text/html\n\n");
printf(
"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"
"<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.1//EN\" \"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd
"<html xmlns=\"http://www.w3.org/1999/xhtml\">\n"
"<link rel=\"stylesheet\" type=\"text/css\" media=\"screen\" href=\"/webif.css\" />"
"<?xml-stylesheet href=\"/include/style.css\" type=\"text/css\" media=\"screen\" ?>"
"<head>\n"
"<title>AVR32 NGW pin toggler</title>\n"
"</head>\n"
"<body style=\"margin: 30px; color: #C3C4D2; background-color: #213242;\">\n"
);
printf("<h1>AVR32 NGW pin toggler</h1>\n");
printf("<p><a style=\"color: inherit;\" href=\"/\">Back to home...</a></p>\n");
printf("<br />");
printf("<p>");
(cont.)
/* Get status on LED */
pio = open("/dev/gpio1", O_RDWR|O_NONBLOCK);
get_status:
if (pio < 0) {
printf("Error: I could not open the GPIO device.</p>\n");
goto error;
} else {
retval = read(pio, &pio_buffer, 4);
if (retval == 4) {
led_on = pio_buffer & (1<<LED_OFFSET) ? 0 : 1;
} else {
if (retval >= 0) {
printf("Error: I could only read %d bytes from the GPIO device.</p>\n", retval);
} else {
if (errno != EAGAIN) {
printf("Error: I could not read from the GPIO device (%d).</p>\n", errno);
}
}
}
}
if (led_on) {
printf("LED is on => ");
} else {
printf("LED is off => ");
}
if (toggle == 1 && led_on == 1) {
unsigned int off = 1<<LED_OFFSET;
write(pio, &off, 4);
printf("turning LED off => ");
toggle = 0;
goto get_status;
}
else if (toggle == 1 && led_on == 0) {
unsigned int on = 0;
write(pio, &on, 4);
printf("turning LED on => ");
toggle = 0;
goto get_status;
}
else if (toggle == 1) {
printf(
"LED was ordered to be toggled, but I could "
"not find out if I was supposed to turn it "
"off or on, I am very sorry :'("
);
}
else if (led_on) {
printf("do you want to turn it off?");
} else {
printf("do you want to turn it on?");
}
printf("</p>\n");
printf("<br />\n");
printf(
"<div><form method=\"post\" action=\"cgipio.cgi\" "
"name=\"cgipio\">\n"
"<input type=\"hidden\" name=\"toggle\" value=\"1\" />\n"
"<input type=\"submit\" value=\"Change LED\" />\n"
"</form></div>\n"
);
close(pio);
error:
printf("</body></html>\n");
return 0;
}
(cont.)
