PCI HARDWARE SUPPORT IN LIA-2 CONTROL SYSTEM

LIA-2 control system is built on cPCI crates with x86compatible processor boards running Linux. Slow electronics is connected via CAN-bus, while fast electronics (4MHz and 200MHz fast ADCs and 200MHz timers) are implemented as cPCI/PMC modules. Several ways to drive PCI control electronics in Linux were examined. Finally a userspace drivers approach was chosen. These drivers communicate with hardware via a small kernel module, which provides access to PCI BARs and to interrupt handling. This module was named USPCI (User-Space PCI access). This approach dramatically simplifies creation of drivers, as opposed to kernel drivers, and provides high reliability (because only a tiny and thoroughly-debugged piece of code runs in kernel). LIA-2 accelerator was successfully commissioned, and the solution chosen has proven adequate and very easy to use. Besides, USPCI turned out to be a handy tool for examination and debugging of PCI devices direct from command-line. In this paper available approaches to work with PCI control hardware in Linux are considered, and USPCI architecture is described.