Undocumented Property Dangers
Designed chips often contain features, which are not completely qualified. These “improvements” are sometimes discovered by accident or through an exhaustive study. At times, the improvements are only discovered because of the user’s unique perspective. In any case, it is important to use these features carefully. Otherwise, there may be consequences.
It happens often that there are additional instructions present in microprocessor or microcontroller instruction sets. For some reason, these instructions don’t get added in the documentation even after they have been included by the designers, and they get left out.
It was first revealed when there were some missing instructions in the Intel 8085, and manufacturers admitted that even though these instructions could be helpful, they are not always guaranteed to be a part of the instruction set. There was a concept of second sourcing that existed a few years ago, but with that, there was no way of telling whether the masks would be entirely identical or if they would be slightly different depending on the source. There was also a concern with whether or not a set of instructions related to software development could be used across various processors.