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Unformatted text preview: original transfer address. In general, using the same register for the base and the index in an addressing mode should be avoided. 5.23 ARM architecture variants
The ARM architecture has undergone a number of revisions in the course of its development. The various architecture versions are described below. Version 1 ARM architecture version 1 describes the first ARM processor, developed at Acorn Computers Limited between 1983 and 1985. These first ARM chips supported only 26-bit addressing and had no multiply or coprocessor support. Their only use in a product was in the ARM second processor attachments to the BBC microcomputer; these were made in very small numbers, but established the ARM as the first commercially exploited single-chip RISC microprocessor. They were also used internally within Acorn in prototypes of the Archimedes personal workstation. 148 The ARM Instruction Set Version 2 The ARM2 chip was sold in volume in the Acorn Archimedes and A3000 products. It was still a 26-bit address machine, but included the 32-bit result multiply instructions and coprocessor support. ARM2 employs the architecture that ARM Limited now calls ARM architecture version 2. The ARM3 chip was the first ARM with an on-chip cache. The architecture was very similar to version 2, but added the atomic load and store (SWP) instruction and introduced the use of coprocessor 15 as the system control coprocessor to manage the cache. The first ARM processor designed by ARM Limited following their establishment as a separate company in 1990 was the ARM6, sold as a macrocell, a stand-alone processor (the ARM60) and as an integrated CPU with an on-chip cache, MMU and write buffer (the ARM600, and the ARM610 used in the Apple Newton). The ARM6 introduced ARM architecture version 3, which had 32-bit addressing, separate CPSR and SPSRs, and added the undefined and abort modes to allow coprocessor emulation and virtual memory support in supervisor mode. ARM architecture version 3 is backwards compatible with version 2a,...
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- Spring '09