Debugger - Hardware Support For Debugging

Hardware Support For Debugging

Most modern microprocessors have at least one of these features in their CPU design to make debugging easier:

• hardware support for single-stepping a program, such as the trap flag.
• An instruction set that meets the Popek and Goldberg virtualization requirements makes it easier to write debugger software that runs on the same CPU as the software being debugged; such a CPU can execute the inner loops of the program under test at full speed, and still remain under debugger control.
• In-System Programming allows an external hardware debugger to reprogram a system under test (for example, adding or removing instruction breakpoints). Many systems with such ISP support also have other hardware debug support.
• Hardware support for code and data breakpoints, such as address comparators and data value comparators or, with considerably more work involved, page fault hardware.
• JTAG access to hardware debug interfaces such as those on ARM architecture processors or using the Nexus command set. Processors used in embedded systems typically have extensive JTAG debug support.
• Microcontrollers with as few as six pins need to use low pin-count substitutes for JTAG, such as BDM, Spy-Bi-Wire, or debugWIRE on the Atmel AVR. DebugWIRE, for example, uses bidirectional signaling on the RESET pin.