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EMBEDDED MULTITASKING

The Easy Way
by Charles Kosina

Start ý An Example ý State Machine Control ý Keyboard Scanning ý Receive Serial Data ý LCD Module ý Transmit Data ý Debugging Techniques ý Other Options ý Sources and PDF

DEBUGGING TECHNIQUES

The built-in JTAG programming and emulation support on the ýF000 make debugging a dream rather than the nightmare it can be with other chips. But, you donýt always get this luxury. Debugging techniques have been covered in previous Circuit Cellar articles, so I wonýt go into too much detail here. [1, 2]

One technique that works well is to send out a character to a serial port representing the current state of a state machine. Listing 6 shows how this is done. It is similar to Listing 3 with added debug instructions. By comparing the current state with the previous state, you send out the debug character only once. State 0 will send out the ASCII character A and so on. This way, you can trace the program flow within a state machine. The penalties are a reduction of the program execution speed and having to use a serial port that may be required for other tasks. Nevertheless, this is one technique that has served me well numerous times.

If you donýt have a UART available, there are other options. A spare I/O port bit can be used with bit-banger software to emulate a serial port. An LCD module can also be used to show the current state. In any case, use the highest bits per second possible to reduce the speed penalty.

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