The Gemini South Adaptive-Optics Imager (GSAOI) has recently been commissioned on the Gemini South telescope. Designed for use with the Gemini GeMS Multi-Conjugate Adaptive Optics System, GSAOI makes use of the HAWAII-2RG (H2RG) On-Detector Guide Window (ODGW) feature where guide windows positioned in each of the four H2RG detectors provide GeMS with tip-tilt and flexure corrections. This paper concentrates on the complex software and firmware required for operating the ODGWs and for delivering the performance required by GeMS. Software architecture, algorithms, performance and the implementation platform for the current on-telescope solution are detailed.