The way you said is very risky. Originally IAP was a high-risk process. In the process from SRAM to Flash, be careful of power failure, and the sooner the action is completed, the better. You can slowly rewrite the contents of Flash while receiving at a low speed, artificially extending the high-risk brushing time by n times.

What's even more frightening is that you don't know anything about Flash. Do you want to write Flash directly without buffering? Don't even use sector buffer? Didn't you indiscriminately ask to erase the whole sector first, and then slowly receive and write byte by byte?

This idea is ok to do papers and research, but if it is really used in products, it will kill a factory.