Simulations and software development for the Hard X-ray Imager onboard ASO-S

China's first solar mission, the Advanced Space-based Solar Observatory (ASO-S), is now changing from Phase B to Phase C. Its main scientific objectives are summarized as '1M2B', namely magnetic field and two types of bursts (solar flares and coronal mass ejections). Among the three scientific payloads, Hard X-ray Imager (HXI) observes images and spectra of X-ray bursts in solar flares. In this paper, we briefly report on the progresses made by the HXI science team (data and software team) during the design phase (till May 2019). These include simulations of HXI imaging, optimization of HXI grids, development of imaging algorithms, estimation of orbital background, as well as in-orbit calibration plan. These efforts provided guidance for the engineering, improved HXI's imaging capability and reduced the cost of the instrument.