Image Number 3 for United States Patent #5729760.
A method of providing access to an input/output (I/O)-mapped register of a computer system is described. The computer system includes a processor operable in a system management mode (SMM), in which the processor 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. Logic circuitry associated with the I/O-mapped register then determines whether the processor is operating in SMM by examining the status of a system management interrupt acknowledge (SMIACT#) output of the processor. If the logic circuitry determines that the processor is operating in SMM, a first, unrestricted type of access by the processor to the I/O-mapped register is provided. Alternatively, if the logic circuitry determines that the processor is not operating in SMM, a second, restricted type of access by the processor to the I/O-mapped register is provided. If the first, unrestricted type of access is provided to the processor, 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.