Memory address decoder with storage for memory attribute information

Abstract

A programmable and testable memory address decoder for a computer system where a static random access memory device is used to store memory configuration information. The computer system includes a processor which is coupled to the memory address decoder via data and address lines. The memory address decoder includes an SRAM for storing a memory map which associates memory attributes with memory ranges or blocks of memory. The memory attributes include: memory residence, caching, write protection of memory ranges, and the decoding of other memory modules. The present invention also includes control logic, a read-back register, and a mode register for controlling the loading and read back verification of the SRAM. The control logic operates the memory address decoder in one of four modes. These modes include: 1) power-up mode, 2) programming mode, 3) read back mode, and 4) normal operation mode. One of these modes is selected by loading the mode register with a value corresponding to the desired mode. A default power up mode is entered after power is first applied to the computer system. When the processor specifies a programming mode, the processor may write data directly into the SRAM. When the processor specifies the read back mode, the contents of the SRAM may be read back by the processor through the read back register. A normal mode may be entered in order to enable access to system memory (DRAM) with memory attribute information.