out the high level language program, even if you cannot compile it for the machine in question. It is not necessary or desirable for the programming of embedded microprocessors to be done in assembly language. Indeed, assembly language should be regarded as a last resort, to be used when compilers are not available, or in very special circumstances. It is, however, necessary for computing scientists and software engineers to have a good understanding of computer architecture, and some exposure to assembly language programming is an important part of achieving overall system programming knowledge. The layout of the assembly language code should follow the high level language structure where possible and sections of code should be marked out clearly in relation to their function. They should be as self contained as possible, and could for example correspond to procedures in the high level language form. Each routine or function should have exactly one exit point. Branches and jumps should remain within a routine or function. They should never be used to jump out, except possibly in the case of errors which require special exception handling. A routine or function may, of course, call another routine or function. A call is generally made by storing parameters and executing a JSR or BSR instruction. The main entry point to a program should normally be to its first instruction, so that when the program is loaded, the entry point can be presumed to be at its lowest address in memory. Symbolic names (defined by labels and equate statements) should be chosen to convey meaning, in exactly the same way that we choose names in a high level language program. Equate statements should be used to define constants or to name registers where they would improve readability of the program. Appropriate comments are even more important in assembly language programming than in high level language programming....
