This paper describes the use of Wind River Simics, a full-platform functional simulator, for early validation of hardware register specifications. The Simics model becomes one of the first consumers of the registers, and can find several types of errors earlier, and sometimes with a wider scope, than hardwarebased validation. The paper is based on an actual experience of collaboration between Simics model developers and hardware architects within Intel during development of an Intel Xeon chip. Simics was proved valuable as a validation tool and contributed to shift-left (reducing time to market) for hardware development.