-; BOOT_DRIVE, part_table_entry and bp must be set up by the code using this driver.
-; first_data_sec is to be set up by calling get_1st_data_sec.
+; BOOT_DRIVE, si and bp must be set up by the code using this driver.
+; (Specifically, si must be a pointer to the partition's partition
+; table entry and bp must be a pointer to the BPB.)
+; Before reading any cluster chains, callers must call get_1st_data_sec
+; and must be careful not to trash ecx after calling it.