The Processor

(CORE/PROCESSOR.JAVA,

CORE/SAMPROCESSOR.JAVA)

The SaM processor is responsible for the loading of a Program object, and the execution of Instruction objects, enclosed within that Program object. Like a real processor, it also provides registers, which assist program execution.

Program Execution

To execute a program, it must first be loaded by the processor. The following methods allow this to happen:

• void init() - initialize the state of the processor
• void load(Program prog) - load a Program object into the processor
• Program getProgram() - obtain the current Program object

Following the successful loading of a program, it may be executed one instruction at a time or all instructions with one call:

• void step() - Step executes one instruction.
• void run() - Run executes all instructions, until the HALT register becomes nonzero

Registers

The SaM Processor implements several registers that allow the Processor to execute programs. These are not used for data storage, but rather are internal processor registers.

• HALT - Execution Status
  Allowed Value: 0 (running) or 1 (stopped)
  Start Value: 0
  It is used to stop the execution of a program.
• PC - Program Counter
  Allowed Value: 0 <= PC < Program Length
  Start Value: 0
  Used to track the instruction that will be executed next.
• SP - Stack Pointer
  Allowed Value: 0 <= SP < Stack Limit
  Start Value: 0
  Used to track the first free memory location on the stack.
• FBR - Frame Based Register
  Allowed Value: 0 &lt;= FBR &lt; Memory Limit
  Start Value: 0
  Used for relative addressing when constructing frames on the stack

Registers can be manipulated using the following methods:

• void set(int register, int value) - set a register to a given value
• int inc (int register) - increment a register by one, and return the result
• int dec (int register) - decrement a register by one, and return the result
• int[] getRegisters() - obtain the register array