There is only one thing i not found exactly: how write operation works?
It says in 82077AA doc, controller starts to read the track on floppy, and after it found sector header, it turns on write gate, and injects write data. While this method on IBM PC (3.5" 1.44 MB 500 kbit/sec MFM encoding), only 1 uSec time difference with that data output pulse makes output bits not "00" but "01" on reading back. Since floppy disc is a mechanical thing, it is always imperfect. And all this will be along a floppy cable fully with parasite loading.
Does it really? I feel it as something unclear, or at least tricky. Could you help me to understand this?
Yes it is ! But there are an VFO/PLL circuit between the FDC and the FDD. This help a lot and allow an +/- 15% speed variation. The sync parts on the floppy is to synchronize the VFO / PLL.