Microprocessor having register bank and using a general purpose register as a stack pointer

In a microprocessor having a register bank, and execution means for executing an instruction, register file means for storing data for a task, the register file means comprising:

• stack pointer means for storing an address for the task;
• general purpose register means comprising a plurality of registers for storing data used by the execution means;
• special purpose register means for storing data relating to the task, the special purpose register means comprising a current bank pointer, a processor status word, a preceding bank pointer, and a program counter;
• and
• bank ram means comprising a plurality of bank blocks, each bank block comprising a predetermined number of unit banks, and each bank block being for storing the data from the general purpose register means,
• wherein, when a current task is switched to another task, the stack pointer means of the current task is set as one of the registers in said general purpose register means, and
• wherein a portion of the processor status word, a bank size field, indicates a size of the bank block such that the number of unit banks in the bank block is changed by the contents of the bank size field.

In a microprocessor having a register bank, and execution means for executing an instruction, a register file storing data for a task, the register file comprising:

• a stack pointer for storing an address for the task;
• a general purpose register group comprising a plurality of registers storing data used by the execution means;
• a special purpose register group storing data relating to the task, the special purpose register group comprising a current bank pointer, a processor status word, a preceding bank pointer and a program counter;
• and
• a bank ram comprising a plurality of bank blocks, each bank block comprising a designated number of unit banks, and being for storing data from the register file for the task,
• wherein, when a current task is switched to another task, the stack pointer of the current task is set as one of the registers in the general purpose register group, and
• wherein a portion of the processor status word, a bank size field, indicates a size of the bank block such that the number of unit banks in the bank block is changed by the contents of the bank size field, and
• wherein the set width of the stack pointer can be changed by the contents of a stack pointer size field in the processor status word.