Design Of Embedded Processors In Protected Mode And Address Of The Management Unit

The study and design of the 32-bit embedded microprocessor AMEx86 supporting protected mode is one part of a military SoC system, in which the 32-bit embedded microprocessor is used to control the whole SoC system.The paper describes how to achieve a virtual memory in a 32-bit embedded microprocessor. In spite of lacking information about the protected mode's realization, the author designs the architecture of AMEx86's virtual memory on the base of Intel 80486, which supports read mode, protected mode and virtual 8086 mode simultaneously. Adopting the method of top-down, the virtual memory is divided into memory mange related unit (Segment Unit and Page Unit) and protection mode related unit (Protection Test Unit, Debug Test Unit and Exception Detect Unit). Data buses and control bused are designed separately for all of the units. VHDL codes are written and simulated. The functional correction is guaranteed by using enough test benches.According to the function's difference of each unit, the author chooses different implement methods. Segment Unit is used to translate the virtual address into linear address, so the adder under the control of microinstruction is introduced to deal with the complex address mode in the x86. Page Unit is used to translate the linear address into the physical address, and the mechanism is fixed correspondingly, so the TLB under the control of the Finite State Machine is introduced. Protection Test Unit is used to accelerate the protection test in complex instructions, so the protection test hardware mechanism under the control of microinstructions is introduced. Debug Exception Unit is used to check if an instruction or data breakpoint is met; so four comparators are introduced to compare four breakpoints at the same time. Exception Detect Unit is used to check all the exceptions in the microprocessors, so a priority circuit is introduced to estimate which exception is reported to the micro controller.As a result, the design turns a 32-bit embedded microprocessor into reality, which is compatible with Intel 80486, supports real mode, protected mode and virtual 8086 mode, supports both 16-bit tasks and 32-bit tasks. According to the characteristics of embedded microprocessors, the Static Instruction Translation method is used in the design of Protection Test Unit, which can decrease the area and complexity of the whole design, so it is suitable for the SoC system.The dissertation work is carried out for 32-bit microprocessor design supporting protected mode inland, which plays a great significance for studying the military microprocessors with own intellectual property. The research work offers design considerations and technological reserves for further advanced microprocessor designs with x86 architectures.