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Our methods for simulating host firmware of the IBM System z9™ facilitated rapid development from first power-on of the system to achieving a platform with a functional operating system. Hundreds of code bugs were eliminated before the code was run on System z9 hardware for the first time. This paper describes the methods used in host firmware simulation for early and efficient firmware tests. The central element for firmware simulation is the Central Electronic Complex Simulator (CECSIM), which offers new facilities to manage the hardware of the simulated system. This management includes concurrent configuration changes of processors, memory, and I/O along with the ability to automatically test complex system functions. To verify correct implementation of the z/Architecture™, we introduced a new test-case framework called the Verification Interface for System Architecture, or VISA, which is used in simulations as well as on the actual system. All of these features are used separately and in combination. A comprehensive and flexible regression environment ensures periodic execution of the test scenarios, and code path coverage measurements show the degree to which the code was actually verified.
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