Microcontroller Solutions TechZone Magazine, April 2011 - Digikey

Figure 14: Character data fi lter usage.
Using the RSS/XML feed reader
Using the RSS/XML feed reader fi rmware is easy:
Figure 12: RSS/XML datafl ow diagram.
The fi lter takes in an XML or RSS data stream and a list of tags.
It outputs only the character data from the selected tags. The
tag list is an array of pointers to those tag strings that need to
be fi ltered.
Normally the fi lter returns 0. When the fi lter processes the “>” in a
tag in the list, it returns into the fi lter array the index+1 for the tag
that it found. Example: after detecting a tag in an RSS or
XML stream the fi lter will return 1. After detecting a
tag in a stream the fi lter will return 2. The fi lter returns 0 if a tag is
not found.
Const unsigned char *tag_filter[] =
{
{(const unsigned char *)”title”},
{(const unsigned char *)”description”},
{(const unsigned char *)””}
};
Figure 13: Sample tag_fi lter pointer array.
1. Set the variable url to the URL or to the desired RSS or XML server.
static const unsigned char url[] =
“http://www.weather.gov/data/current_
obs/KUGN.rss”;
2. Set the tag_fi lter[] to the type of data you want to display.
For RSS feeds, and would be a fi rst choice.
For XML feeds, this could be any tag name depending on the
information.
const unsigned char *tag_filter[] =
{
{(const unsigned char *)”title”},
{(const unsigned char *)”description”},
{(const unsigned char *)””}
};
3. Set the character buffer size large enough to collect your
fi ltered data.
#define RSS_CHARACTER_BUFF_SIZE2048
4. Compile the project and fl ash it to the board.
After the TCP/IP stack comes up, these actions occur:
1. The DHCP client automatically acquires an IP address and DNS IP
address.
2. It displays and speaks a title screen.
3. It connects to the server specifi ed in the URL.
4. The status of the connection is displayed and spoken.
5. The fi le is downloaded from the server using the HTTP client.
6. After the connection closes, the fi le is displayed and spoken.
7. The RSS/XML feed reader sleeps, waiting for either SW1 or SW2
to be pushed. When that happens, a connection is initiated to
the server specifi ed in the URL that starts the download/display/
speak process all over again.
34