Introduction to ARM MMU

ARM MMU

The ARM Memory Management Unit (MMU) is a hardware unit of the ARM processor that helps facilitate the virtual memory management of the system. It enables an operating system to create and manage multiple address spaces, and to control which areas of memory are accessible to a process at any given time. The MMU is also responsible for providing memory protection and data sharing across multiple processes.

Features & Functionality

The ARM MMU has a range of features that make it suitable for a variety of applications. These features include:

• Translation lookaside buffer (TLB): This is a mechanism used to cache page table entries, enabling faster translation of virtual addresses into physical addresses.
• Page tables: These are structures used to define how memory is divided and managed.
• Memory protection: This feature enables the MMU to ensure that processes do not access memory locations that belong to other processes.
• Data sharing: The MMU can provide facilities to allow different processes to share memory without necessarily allowing either one to modify the other’s data.
• Virtual memory: The MMU can provide a means of mapping virtual addresses to physical addresses.

Implementation

The ARM MMU is provided as part of the ARMv6 processor core, along with supporting circuitry. This circuitry includes the TLB, which is a memory structure used to cache page table entries. Each entry in the TLB contains an address mapping from the virtual address to the associated physical address.

The MMU also provides access control mechanisms, which can be used to specify which processes have access to specific memory regions. This enables memory protection, so that processes are prevented from accessing memory that does not belong to them. It also allows for data sharing between processes if this is desired.

Finally, the MMU can also provide support for virtual memory. This allows the operating system to create multiple address spaces, and map virtual addresses to physical addresses. This makes it possible for processes to access memory without knowing the exact physical locations of that memory.