5. The following code is executed by an ARM processor with each instruction exec

Question

5. The following code is executed by an ARM processor with each instruction executed exactly once: MOV r0,#0 LDR r1,#10 MOV r2,#0 ADR r3,c ADR r5,x ; loop test ; use r0 for i, set to 0 get value of N for loop termination test ; use r2 for f, set to 0 ; load r3 with address of base of c array ; load r5 with address of base of x array loop CMP r0,rl BGE loopend ;ifi N, exit loop loop body LDR r4,[r3,r0] LDR r6,[r5,r0] MUL r4.r4.r6 ADD r2,r2,r4 get value of clil get value of xi] compute cl*xi] add into running sum f update loop counter ADD r0,ro,#1 B loop ; add 1 toi ; unconditional branch to top of loop Assume that the following code fragment was loaded at 0x0000 MOV r0, #0 LDR r2, #10 MOV r2, #0 0001 0010 0011 0100 0101 loop CMP rO, r1 0110 ADR r5, x BGE loopend

Explanation / Answer

ARM machines have a history of living up to the expectations of their developers, right from the very first ARM machine ever developed. It all began in the 1980s when Acorn Computers Ltd., spurred by the success of their platform BBC Micro wished to move on from simple CMOS processors to something more powerful, something that could stand strong against the IBM machines launched in 1981. The solutions available in the market like the Motorola 68000 were not powerful enough to handle graphics and GUIs leaving only one option with the company, make their own processor.

Inspired by the making of 32 bit processors by some undergraduates at Berkeley and a one man design center Western Design Center, Phoenix, Steve Furber and Sophie Wilson of Acorn Ltd. set out to make their own processors. Sophie developed the instruction set and simulated it on the BBC Basic which convinced many in the company that it was not just anything half hearted shot aimed in darkness. With the support and permission of the then CEO Hermann Hauser, the ARM project formally took off in 1983 with VLSI Technology as their silicon partner, to produce an ARM processor with latencies as low as that of the 6502. The first ARM core dubbed as ARM1 was delivered by VLSI Technology in 1985. This processor used in conjunction with the BBC Micro helped in the development of the next generation called ARM2. 1987 saw the release of ARM Archimedes.

Acorn floated a new company Advanced RISC Machines Ltd. solely dedicated for ARM core development. In 1992, Acorn won the Queen’s Award for Technology for the ARM. Apple and ARM collaborated to develop the ARM6 cores on which the Apple Newton PDAs were based. Later, the technology was also transferred to Intel over a settlement of lawsuit. Intel further modified it and developed its own high performance line XScale, now sold to Marvell. ARM Inc. is involved with developing cores primarily while its licensees make microcontroller and processors, the most popular being the ARM7TDMI machines. Some prominent licensees of ARM machines are Alcatel Lucent, Apple, Atmel, Cirrus Logic, Freescale, DEC, Intel, LG, Marvell, Microsoft, Nvidia, Qualcomm, Samsung, Sharp, ST microelectronics, Symbios Logic, Texas Instruments, VLSI Technology, Yamaha, Zilabs etc.

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