Virtual memory management is always a very essential issue of the modern microprocessor design. A memory management unit (MMU) is designed to implement a virtual machine for user programs, and provides a management mechanism between the operating system and user programs. This paper analyzes the tradeoffs considered in the MMU design of Unity 11 CPU of Peking University, and introduces in detail the solution of pure hardware table walking with two level page table organization. The implementation takes care of required operations and high performances needed by modern operating systems and low costs needed by embedded systems. This solution has been silicon proven, and successfully porting the Linux 2.4.17 kernel, the XWindow system, GNOME and most application software onto the Unity platform.
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