In my previous post, I finally started to make some progress with my Windows Embedded CE project. I was able to get a simple test application running which could send and receive messages via a serial port on my iCop eBox 2300 computer. I first sent messages to a host computer using an RS232 crossover cable. Once I confirmed that there were no problems sending and receiving messages or changing the baud rate, I cut the cable and plugged in a pair of XBee modules in place of the crossover cable. I wasn't ready to install custom device drivers in my Windows Embedded CE operating system image, so I used an XBee serial explorer ordered from SparkFun to connect an XBee to the eBox computer. After confirming that everything was working as expected, I was ready to modify the serial port test application to run my wireless light controller.



Before I continue, I want to briefly reflect on some of the steps required to get my program to finally work. I initially suspected that I had a serial port buffer overrun problem, since I couldn’t send messages longer than 16 characters. When I noticed that my serial port test program would hang at the end of a serial port transmission of any length, I started to think that the problem may be interrupt related instead of buffer related. If the serial port call was waiting for a “buffer empty” signal before it returned control to my program, hanging at the end of a transmission meant that it never got that signal. Since I had been editing a number of serial port settings in the BIOS and registry while trying to disable or reroute serial debugging messages, I might have inadvertently modified a critical registry key. Rather than retrace my steps and restore the factory settings, I started with a clean copy of the BSP to build the operating system image. I had also notice that many of the build directories for my Visual Studio 2005 installation were pointing to a more recent version of Visual Studio on my computer. After mapping all the directories to the correct location, I rebuilt the operating system using clean copies of all the drivers and BSP.

Finally, everything worked flawlessly when I tested the new operating system with the simple Visual Basic serial port terminal example from Samuel Phung's Windows Embedded CE 6.0 website.




When the button is pressed, a state variable is checked to see if the light corresponding to the button is on or off. If it is currently off, the command to turn it on is sent to the serial port, the state variable is updated, and the button background color is changed to yellow. If the light was on when the button was pressed, the off command is sent, the state variable is updated, and the background color is changed to gray.

I had to think about sending the command data in the appropriate format. My Arduino code is looking for byte values not ASCII text, but the VBSerial.Write() function needs a string as an argument. This is done very easily using the CHR() function.