Stack and Subroutines

• Work Huang Chapter 4 exercise problems E4.[5, 11] . Notes:
  • First, work the short problem E4.11. Include all the details in the resulting stack frame, including listing each byte with its contents (actual numbers if known), showing SP offsets for every byte, showing the initial and final positions of the SP.
  • For problem E4.5, you should copy and modify as needed the example program (Example 4.6) from the textbook as the heart of the subroutine (code available on the student CD). Note the following corrections you must make to the example:
    • Delete the "buf2" memory location.
    • Delete the line "clr   buf2".
    • Change the line "addd   buf2" to "addd   buf1".
    • Insert "swi" after the line "staa   error", before the "done" label.
  • Write THREE versions (a,b,c) of problem E4.5 as follows.
    • Problem E4.5a will use register parameter passing, exactly as described in the textbook problem, with no stack operations (except for return address); thus not saving state or creating local temp variables on the stack. Note: this is NOT good practice!
    • Problem E4.5b will be identical except that it will use global memory parameter passing plus save/restore all used registers on the stack; but do not create any local temp variables on the stack.  Note: this is NOT good practice, either!
    • Problem E4.5c will be identical except that it will use the stack for parameter passing, register saving, and allocation of all local temporary variables; Note: this IS good practice. As in problem E4.5b, preserve all used registers in the subroutine.
  • For each version of problem E4.5, write both a main calling routine and a called subroutine, both in one source file. Follow all the guidelines about program and subroutine styles and documentation given in our Program Format web page, including pseudocode. As discussed in class, this code should be thoughtfully designed and modular, so isolate everything possible that is related to the subroutine within the subroutine section of the code. The main routine must create a string to be converted, call the subroutine, pass the input parameters to it appropriately, and retrieve the output parameters (results) from the subroutine; if the conversion was successful, store the resulting number in memory and clear the error flag, else set an error flag in memory; then stop execution. The code must be complete assembly language source files, that could be assembled, downloaded, and executed on our Dragon12 board using the D-Bug12 monitor.
  • Copy all your files for problems (E4.5(a,b,c)) to your ClassDrop folder at \\athena.pclab.tntech.edu\classdrops\ECE\ECE3120-Haggard\your-name\HW12\.