Data processor and method of controlling the same

A method of controlling a data processor comprising:

• a buffer for storing said branch instructions and a plurality of instructions;
• a first controller for decoding instruction other than said branch instructions read from said buffer and controlling execution of said instruction other than said branch instructions;
• a first storage unit having at least a plurality of registers for writing addresses and data required for execution of said plurality of instructions, and a register with a particular number assigned to one of said plurality of registers and for writing target addresses required for execution of said branch instructions therein, and having a plurality of write ports and read ports for selecting registers with numbers designated by said first controller;
• a second storage unit connected to a particular read port of said plurality of read ports, for storing contents of a register read out into said particular read port temporarily;
• a register number selecting means for controlling said particular read port so as to connect said register with said particular number to said second storage unit when said first controller is not using said particular read port;
• a second controller for interpreting said branch instructions from said buffer to control execution of said branch instructions based on said target address stored in said second storage unit;
• and
• a flag register for indicating whether said register number designated by said first controller coincides with particular register number into which said target address is written,
• wherein branch control comprises the steps of:
• selecting said register number designated by said first controller from said first storage unit by said write port in said first storage unit;
• writing said target address into selected register number, detecting whether said designated number coincides with said particular number, and resetting said flag register if both numbers coincide with each other or if contents of said register with said particular number, by said first controller;
• controlling said particular read port so as to connect said register with said particular number to said second storage unit unless said particular read port is being used by said instruction other than said branch instructions, by said register number selecting means;
• controlling said flag register into a set state when contents of said register with said particular number is copied in said second storage unit, by said first controller;
• and
• utilizing contents of said second storage unit as said target address by said second controller if said target address using said contents of a register in said first storage unit as said target address is detected and said register number designated by said target address coincides with said particular number and then a coincidence between said contents in said second storage unit and said contents of said register with said particular number is confirmed by said flag register.