You must implement the TRAP instruction as
the LC-3b ISA defines in Appendix A. However, you
do not need to implement the TRAP routines. The
trap vector table will be initialized to all zeroes by the
shell code provided. Thus, whenever a TRAP
instruction is processed, PC will be set to 0. The shell code
provided will halt the simulator whenever PC becomes 0.
You do not have to implement the RTI
instruction for this lab. You can assume that the input file
to your simulator will not contain any RTI
instructions.
For this assignment, you can assume that the programmer will always give aligned addresses, and your simulator does not need to worry about unaligned cases.
If you decide to use any of the math functions in math.h, you also have to link the math library by using the command:
gcc -lm -ansi -o assemble assembler.cYou do not need to implement memory mapped I/O for this lab.
You may assume that the code running on your simulator has been assembled correctly and that the instructions your simulator sees comply with the ISA specification.
In your code that you write for lab 2, do not assign the current latches to the next latches. This is already done in the shell code.
The Low16bits macro provided in the shell code
zeroes out the top 16 bits of its argument, like so:
#define Low16bits(x) ((x) & 0xFFFF)You may use this macro to avoid getting values like xFFFFFFFF
in architectural registers. The variables in your C program
are 32-bit values, so the number -1 is xFFFFFFFF.
However, the LC-3b is a 16-bit machine, in which -1 is
represented as xFFFF. Thus, you have to make
sure that when you store a value in a variable representing an
LC-3b register, you mask it properly (for example, using the
macro given above).
LEA should NOT set the machine's condition codes, despite what the current reference documents may say.