PRIM system - A framework for emulation - based debugging tools

For some applications the native machine is not the system of choice in which to develop software, as when the target machine is unavailable (because it is still being developed, is obsolete, or is inaccessible) or inconvenient (as when there is minimal target-system support for debugging). In such cases, simulation or emulation may be preferred. Simulation has the advantage of giving the user intimate access to the target machine, usually through a rich debugging package. Typically this richness is achieved at a high development cost for the simulator and at a target-system performance degradation of f~ur or more orders of magnitude. Emulation can offer processing speeds comparable to the target system (even faster, for slow target machines), but typically does not support a rich debugging environment. In designing the PRIM system, we have attempted to retain the best features of both the simulation and emulation approaches while at the same time minimizing their disadvantages. PRIM provides a sharable, uniform framework for running emulations of target machines; within that framework is a rich user interface that supports interactive targetsystem and emulator debugging. When the user is not engaged in debugging, the target system runs at emulator speeds, but a sophisticated debugging package is available immediately when needed. PRIM was developed within a . modem timesharing system so as to provide convenient access, a file system, resource management, and a large set of utilities without the cost of developing yet another operating system.