Emulating a delayed exception on a digital computer having a corresponding precise exception mechanism

摘要

A digital computer system comprises a precise exception handling processor and a control subsystem. The precise exception handling processor performs processing operations under control of instructions. The precise exception handling processor is constructed in accordance with a precise exception handling model, in which, if an exception condition is detected in connection with an instruction, the exception condition is processed in connection with the instruction. The precise exception handling processor further includes a pending exception indicator having a pending exception indication state and a no pending exception indication state. The control subsystem provides a series of instructions to the precise exception handling processor to facilitate emulation of at least one emulated program instruction. The emulated program instruction is constructed to be processed by a delayed exception handling processor which is constructed in accordance with a delayed exception handling model, in which if an exception is detected during processing of an instruction, the exception condition is processed in connection with a subsequent instruction. The series of instructions provided by the control subsystem in emulation of the emulated program instruction controls the precise exception handling processor toP P(i) determine whether the pending exception indicator is in the pending exception indication state and, if so, to invoke a routine to process the pending exception and condition the pending exception indicator to the no pending exception indication statePP (ii) perform processing operations in accordance with the emulated processing instruction; andPP(iii) if an exception condition is detected during the processing operations, to invoke an exception handler in accordance with the processor's precise exception handling model to condition the pending exception indicator to the pending exception indication state, so that the exception condition will be processed during processing operations for a subsequent emulated program instruction.