SYSTEM FOR CONTROLLING ACCESS TO A REGISTER MAPPED TO AN I/O ADDRESS SPACE OF A COMPUTER SYSTEM

摘要

A method of providing access to an input/output (I/O) mapped register (60) of a computer system (18) is described. The computer system (18) includes a processor (20) operable in a system management mode (SMM), in which the processor (20) accesses a dedicated system management memory space, a real mode, a protected mode and a virtual 8086 mode. The method includes the steps of firstly receiving an access request at the I/O mapped register (60). Logic circuitry (64) associated with the I/O mapped register (60) then determines whether the processor (20) is operating in SMM by examining the status of a system management interrupt acknowledge (SMIACT#) output of the processor (20). If the logic circuitry (64) determines that the processor (20) is operating in SMM, a first, unrestricted type of access by the processor (20) to the I/O mapped register (60) is provided. Alternatively, if the logic circuitry (64) determines that the processor (20) is not operating in SMM, a second, restricted type of access by the processor (20) to the I/O mapped register (60) is provided. If the first, unrestricted type of access is provided to the processor (20), it performs an operation, under the direction of code stored in the dedicated system management memory address space, on the contents of the I/O mapped register (60).