Using Simulation to Develop and Port Software

1 Abstract Among the tools developed to support Digital's Alpha AXP program were four software simulators. The Mannequin and ISP instruction set simulators were used to port the OpenVMS and OSF/1 operating systems to the Alpha AXP platform. The Alpha User-mode Debugging Environment (AUD) allowed Alpha AXP user-mode code to be debugged with support from the OpenVMS VAX run-time environment on VAX hardware. AUD was built from a combination of new and existing Digital software components. The Alpha User-mode Debugging Environment for Translated Images (AUDI) allowed translated images to be debugged on a simulator running on a VAX computer. With these debugging environments, user-mode applications and code components could be tested before Alpha AXP hardware and operating system software were available. Digital developed several software simulators to support its Alpha AXP program.[1] These tools enabled engineers to develop and port software for the 64-bit RISC Alpha AXP architecture concurrently with hardware development. The simulators were used for a variety of purposes including porting, testing, verification, and performance analysis. This paper discusses four Alpha AXP software simulators: Mannequin, ISP, AUD, and AUDI. 2 The Mannequin and ISP Simulators Two Alpha AXP instruction set simulators, Mannequin and ISP, were used to port operating systems to the Alpha AXP platform. The OpenVMS group used the Mannequin simulator to port the OpenVMS VAX system to the Alpha AXP platform. Likewise, the OSF/1 group used the ISP simulator in their port of the ULTRIX and OSF/1 operating systems to the Alpha AXP platform. Both simulators were also used for architectural and design verification, and for performance modeling. The Mannequin simulator grew out of a simulator developed for an earlier RISC project at Digital. The ISP simulator was written anew by engineers closely associated with the Alpha AXP architecture. The two development groups were requested to boot their respective operating systems on the simulators before attempting to boot on the Alpha Demonstration Unit (ADU), the Alpha AXP prototype hardware.[2] The simulators were so successful in tracking the Alpha AXP architecture and in rooting out software bugs that the OSF/1 group was able to boot the ULTRIX operating system on the hardware on the first attempt. The OpenVMS group had similar success and booted the OpenVMS AXP operating system in a few hours.