ARM.SoC.Architecture

Provided these sets do not overlap the cache and mmu

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Unformatted text preview: ation scheme was used on the early ARM memory controller chips used in the Acorn Archimedes machines. Referring to Figure 10.12 on page 288, the translation hardware can be a CAM; the physical page number store is a simple hardwired encoder, and the CAM has one entry for each physical page. The Acorn memory controller chips had CAMs with 128 entries and a page size that varied according to the amount of physical memory in the system. A 1 Mbyte system had 8 Kbyte pages, a 4 Mbyte system had 32 Kbyte pages. To extend beyond 4 Mbytes, the page size stayed at 32 Kbytes and a second memory controller was added. The CAMs were maintained by software, so no complex table-walking hardware was required. The full translation tables were entirely defined by software. Example 10.1 Exercise 10.1.1 Exercise 10.1.2 Example 10.2 Exercise 10.2.1 Estimate the die area of a 128-entry inverted page table compared with a 64 entry TLB, assuming that one bit of CAM requires twice the area of one bit of RAM. Architectural Support for Operating Systems Summary of chapter contents The role of an operating system is to provide an environment where several programs may run concurrently with a minimal risk of unwanted interference between them but with support for safe data sharing. The operating system should also provide a clean interface to the hardware facilities of the machine. Interference between processes is minimized by memory management and protection schemes which enable each process to access only its own area of memory. The process is given its own view of the system memory, and when a process switch takes place the memory view is dynamically transformed to that of the new process, with all the memory used by the previous process being removed from sight. This requires sophisticated hardware support if it is to operate efficiently. Data sharing implies a loophole in the protection scheme which must be controlled with great care. Haphazard access to shared structures can lead to the most obscure form...
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This document was uploaded on 10/30/2011 for the course CSE 378 380 at SUNY Buffalo.

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