The radiofrequency (RF) acceleration system of the Large Hadron Collider (LHC) comprises 8 superconducting 400MHz cavities in each of the two LHC rings, with each cavity driven by a klystron amplifier. The phase and radial position of the beam and the accelerating voltage and phase in the cavities are controlled by a complex system of feedbacks collectively known as the low-level RF (LLRF) system. The LLRF system is implemented in mixed analogue and digital hardware modules using a custom form factor based on the VMEbus platform. The control system, from the crate controller CPU and timing modules, through the front-end software and communications middleware to the application software interface, is implemented using tools and components provided by the CERN accelerator controls group, such as the new Front-End Software Architecture (FESA). This paper describes the controls architecture of the LLRF system and discusses the hardware and software choices made in its implementation
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