Difference between revisions of "National Semiconductor 16550 UART"
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The XINU backends have been equipped with serial ports that are representative of the National Semiconductor 16550 UART. Documentation on the 16550 UART can be found at [http://www.national.com/ds.cgi/NS/NS16C552.pdf http://www.national.com/ds.cgi/NS/NS16C552.pdf]. | The XINU backends have been equipped with serial ports that are representative of the National Semiconductor 16550 UART. Documentation on the 16550 UART can be found at [http://www.national.com/ds.cgi/NS/NS16C552.pdf http://www.national.com/ds.cgi/NS/NS16C552.pdf]. | ||
Revision as of 21:31, 11 July 2007
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This page may require cleanup to meet academic/public standards. A page requiring cleanup may have been hastily added or difficult to understand by outsiders. More information can be found on the talk page. |
The XINU backends have been equipped with serial ports that are representative of the National Semiconductor 16550 UART. Documentation on the 16550 UART can be found at http://www.national.com/ds.cgi/NS/NS16C552.pdf.
Why serial ports are added
A normal user will interact with the WRT54GL using a pretty web interface, which runs as a stripped down web server that listens to port 80 and provides access to basic configuration opitions.
When we load our own code to be executed, we are starting with a blank slate--anything we want the hardware to do we have to code ourselves. This makes the first steps very difficult: we can't exactly check the web interface to see if we're doing things right. How can we know that our code is working properly if there is no way of getting feedback?
Enter the serial console. A serial connection is essentially two wires (transmit, and receive) over which two computers can agree on timing and transmit bytes to each other. In our case, these bytes will represent characters, and the characters will be the output and input of a console. LinkSys actually includes the hardware for two serial ports on the WRT54GL as headers on the circuit board. OpenWRT (and LinkSys..?) runs a console on first serial port by default, so that once a serial connection is properly made, all one has to do is press enter for a console to appear.
The serial device is a much more basic service than say, communicating over the network, so it is a likely candidate for our first form of communication to achieve. We could have also tried for maybe the LED lights, but it would be incredibly difficult to intepret output and also impossible to get input using them. So the serial port was the goal.
