Microprocessor with an external command mode for diagnosis and debugging

A computer circuit including a processor, said circuit operating in a processor-driven mode wherein the circuit executes a series of macroinstructions stored in a computer memory, and also for operating in a probe mode wherein the circuit receives an external signal that may include externally supplied commands, and externally supplied probe mode microinstructions, said circuit comprising:

• a mode selection unit for selecting between the processor-driven mode and the probe mode;
• an access port, including
• means for receiving and sending the external signal,
• means for sending information to the processor and receiving information from the processor, and
• control logic for controlling the interface between the port and the processor;
• a probe instruction register for holding a probe mode microinstruction received in the external signal;
• a probe data register for holding data;
• an execution unit for executing microinstructions;
• and
• a microinstruction multiplexer coupled to the mode selection unit that selects a microinstruction to be provided to the execution unit, said microinstruction multiplexer selecting one of inputs including an input microinstruction decoded from a macroinstruction from the processor-driven path and an input probe mode microinstruction from the probe instruction register.

A microprocessor for selectively operating in a processor-driven mode wherein the microprocessor is responsive to a series of macroinstructions stored in a computer memory, and for operating in an external command mode wherein the microprocessor is responsive to externally supplied microinstructions, said microprocessor comprising:

• means for selecting between the external command mode and the processor-driven mode;
• a decoder for receiving and decoding stored macroinstructions;
• an execution unit for executing microinstructions;
• means for supplying an externally supplied microinstruction to the execution unit directly, thereby bypassing the decoder when the external command mode is selected;
• and
• means for supplying one or more microinstructions from a decoded macroinstruction from the decoder to the execution unit when the processor-driven mode is selected;
• updating means for implicitly updating the processor state information before supplying said decoded microinstruction to the execution unit when said processor-driven mode is selected, said processor state information including an instruction pointer;
• and
• means for bypassing said updating means when the external command mode is selected.

An external command method of operating a microprocessor having a pipelined instruction flow through a processor-driven instruction path that implicitly updates state information, including the instruction pointer, before supplying a microinstruction to an execution unit, said external command method comprising the steps of:

• providing an external instruction path coupling an external signal with the execution unit, said external instruction path bypassing the implicit updating of the processor-driven instruction path which would otherwise result from decoding a stored macroinstruction;
• supplying a microinstruction through the external instruction path for execution in the execution unit, bypassing the macroinstruction decoder in the processor-driven instruction path;
• and
• executing said microinstruction in the execution unit.

A method of operating a microprocessor including a decoder and an execution unit, comprising the steps of:

• selecting a mode of executing microinstructions, said modes including a probe mode method of executing microinstructions supplied by the external path and a processor-driven mode method of executing microinstructions which resulted from the decoding of macroinstructions stored in memory;
• if the processor-driven mode has been selected, then executing microinstructions comprises the steps of
• fetching a macroinstruction from memory and providing it to a decoder,
• decoding the macroinstruction to provide one or more microinstructions that are applied, one after the other, to an execution unit,
• updating processor state information including an instruction pointer, and
• executing microinstructions supplied from the decoder;
• and
• if the probe mode has been selected, then executing microinstructions comprises the steps of
• providing an externally supplied microinstruction to the execution unit, thereby bypassing the decoder and not updating the instruction pointer and other processor state information, and
• executing the externally supplied microinstruction.

A computer circuit including a processor operating in one of a processor-driven mode in which the circuit executes a series of macroinstructions stored in a computer memory and a probe mode wherein the processor receives and processes an external signal, said circuit comprising:

• an external control unit that provides said external signal including an externally supplied command and probe mode instruction;
• an access port coupled to said external control unit, including
• a circuit for receiving and sending the external signal;
• a circuit for sending information to the processor and receiving information from the processor;
• control logic for controlling the interface between the access port and the processor, and
• a probe instruction register for holding a probe mode microinstruction received in the external signal;
• an execution unit for executing microinstructions;
• a mode selection unit for selecting between the processor-driven mode and the probe mode;
• and
• a microinstruction multiplexer that selects a microinstruction to be provided to the execution unit, said microinstruction multiplexer having inputs including a microinstruction decoded from a macroinstruction from the processor-driven path and a probe mode microinstruction from the probe instruction register, said microinstruction multiplexer coupled to the mode selection unit to select one of said inputs.