A detailed analysis of an impulsive solar flare of 1999 September 17 was carried out using microwave, soft, and hard X-ray data. The flare showed pronounced nonthermal processes and was accompanied by a cusplike structure in soft X-rays in the decay phase, manifesting features attributed to different flare models. The results suggest that important nonthermal and strong thermal processes in the impulsive phase were caused by interactions between low-lying magnetic loops, and that the overlying bright soft X-ray loops accompanied by a cusplike configuration in the decay phase had no relation to major nonthermal and thermal flare processes in the impulsive phase. A possible microwave loop-top source was observed above one of the overlying bright soft X-ray loops. Its time profile was completely different from those of the main microwave and hard X-ray sources.