Reverse Engineering the ARM1, with History, Simulator, Barrel Shifting, and More
Almost every smartphone uses a processor based on the ARM1 chip created in 1985. The Visual ARM1 simulator shows what happens inside the ARM1 chip as it runs; the result is fascinating but mysterious. In this article, I reverse engineer key parts of the chip and explain how they work, bridging the gap between the puzzling flashing lines in the simulator and what the chip is actually doing. I describethe overall structure of the chip and then descend to the individual transistors, showing how they are built out of silicon and work together to store and process data.
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