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POUnravelling Assembly Language Spaghetti Code
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copied!<p>I've inherited a 10K-line program written in 8051 assembly language that requires some changes. Unfortunately it's written in the finest traditions of spaghetti code. The program--written as a single file--is a maze of CALL and LJMP statements (about 1200 total), with subroutines having multiple entry and/or exit points, if they can be identified as subroutines at all. All variables are global. There are comments; some are correct. There are no existing tests, and no budget for refactoring.</p> <p>A little background on the application: The code controls a communications hub in a vending application that is currently deployed internationally. It handles two serial streams simultaneously (with the help of a separate communications processor) and can be talking to up to four different physical devices, each from a different vendor. The manufacturer of one of the devices recently made a change ("Yeah, we made a change, but the software's absolutely the same!") which causes some system configurations to no longer work, and is not interested in unchanging it (whatever it was they didn't change).</p> <p>The program was originally written by another company, transferred to my client, then modified nine years ago by another consultant. Neither the original company, nor the consultant, are available as resources.</p> <p>Based on analysis of the traffic on one of the serial buses, I've come up with a hack, which appears to work, but it's ugly and doesn't address the root cause. If I had a better understanding of the program, I believe I could address the actual problem. I have about one more week before the code's frozen to support an end-of-the month ship date.</p> <p>Original question: I need to understand the program well enough to make the changes without breakage. Has anyone developed techniques for working with this sort of mess?</p> <p>I see some great suggestions here, but am limited by time. However I may have another opportunity in the future to pursue some of the more involved courses of action. </p>

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