Processor condition sensing circuits, systems and methods

A data processing device, comprising:

• a program counter for holding an address of an instruction currently being processed by said data processing device;
• means for causing said program counter ordinarily to count through a continuous sequence of addresses;
• a control circuit for entering into said program counter an out-of-sequence address that establishes within the sequence of program counter addresses an address discontinuity defined by the out-of-sequence address and the address which immediately preceded the out-of-sequence address in the program counter;
• a program counter stack, and means for selectively pushing an address from said program counter onto said program counter stack;
• and
• a trace stack, said control circuit including means responsive to the address discontinuity for pushing the out-of-sequence address onto said trace stack.

A method of tracing operations of a data processing device having a program counter which normally counts through a continuous sequence of addresses at which instructions to be processed by the data processing device reside, comprising the steps of:

• providing the data processing device with a trace stack which is separate from a program counter stack of the data processing device;
• determining whether a program counter address is an out-of-sequence address that establishes within the sequence of program counter addresses an address discontinuity defined by the out-of-sequence address and the address which immediately precedes the out-of-sequence address;
• and
• responding to a detected address discontinuity by pushing the out-of-sequence address onto the trace stack.