I have interfaced 256Mb sdcard with stm32f051 using FATFS driver, find_volume() function is giving FR_NO_FILESYSTEM response because ld_word(fs->win + BS_55AA) != 0xAA55. Please give me some solution for this issue.
Yes, it is failing because the routines underneath aren't supplying the right data.
Review/dump the data being read from the media, make sure they are actually an MBR or BPB sector the file system can use.
I'd recommend dumping the data from the read function in the DISKIO layer.