z/CECSIM: An efficient and comprehensive microcode simulator for the IBM eServer z900

An IBM eServer zSeries system uses various types of microcode (firmware) that implement functions such as the execution of complex instructions in the CPUs, I/O operations performed by the system assist processors (SAPs), the management of logical partitions (LPARs), and control by the support element (SE). Each microcode component must be verified by itself and in conjunction with the others. Tight development schedules and a very limited supply of expensive engineering hardware make it desirable to perform this verification in a simulation environment. For the development of the z900, a new microcode simulator, the z/CECSIM (Central Electronic Complex Simulator), was successfully implemented. Several microcode components are connected in a single simulation environment, thereby allowing an unprecedented amount of development, integration, and testing without the use of engineering hardware. z/CECSIM creates a virtual zSeries CEC on VM/ESA or z/VM that allows the simulation of zSeries microcode. It executes the instruction stream as completely as possible on the underlying hardware. Only instructions that are newly introduced with the system being developed or that perform a microcode-internal function are simulated. Additional software models mimic the behavior of I/O and coupling channels. An optional SE connection allows verification of interactions between the CEC and its support element.