More fixes in fat1X_mkfs

- CHS are now explicitly set in partutils.py for some well-known 3.5 inch floppy disks, fixing format capabilities in mkfat.py
- less assumptions about heads and sectors per track in mkfat.py

FATtools/mkfat.py

@@ -118,9 +118,10 @@ def fat12_mkfs(stream, size, sector=512, params={}):
     boot.chPhysDriveNumber = 0
     boot.uchSignature = 0x29
     boot.wBootSignature = 0xAA55
-    boot.wSectorsPerTrack = 18 # CAVE! This is true with floppies, not little HDDs (20MB, 120MB etc.)
-    #~ boot.wHeads = 2
-    boot.wHeads = partutils.size2chs(size,1)[1] # not used with LBA
+    c,h,s = partutils.size2chs(size,1)
+    if DEBUG&1: log("fat12_mkfs C=%d, H=%d, S=%d", c, h, s)
+    boot.wSectorsPerTrack = s
+    boot.wHeads = h # not used with LBA
 
     boot.pack()
     #~ print boot
@@ -277,8 +278,10 @@ def fat16_mkfs(stream, size, sector=512, params={}):
     boot.chPhysDriveNumber = 0x80
     boot.uchSignature = 0x29
     boot.wBootSignature = 0xAA55
-    boot.wSectorsPerTrack = 63 # not used w/o disk geometry!
-    boot.wHeads = partutils.size2chs(size,1)[1] # not used with LBA
+    c,h,s = partutils.size2chs(size,1)
+    if DEBUG&1: log("fat16_mkfs C=%d, H=%d, S=%d", c, h, s)
+    boot.wSectorsPerTrack = s
+    boot.wHeads = h # not used with LBA
 
     boot.pack()
     #~ print boot
@@ -448,8 +451,10 @@ def fat32_mkfs(stream, size, sector=512, params={}):
     boot.chPhysDriveNumber = 0x80
     boot.chExtBootSignature = 0x29
     boot.wBootSignature = 0xAA55
-    boot.wSectorsPerTrack = 63 # not used w/o disk geometry!
-    boot.wHeads = partutils.size2chs(size,1)[1] # not used with LBA
+    c,h,s = partutils.size2chs(size,1)
+    if DEBUG&1: log("fat32_mkfs C=%d, H=%d, S=%d", c, h, s)
+    boot.wSectorsPerTrack = s
+    boot.wHeads = h # not used with LBA
 
     fsi = fat32_fsinfo(offset=sector)
     fsi.sSignature1 = b'RRaA'

FATtools/partutils.py

@@ -59,7 +59,27 @@ def lba2chs(lba, hpc=0):
 
 def size2chs(n, getgeometry=0):
     lba = n//512
-    for hpc in (2,16,32,64,128,255): # 2 is typical for 720K DS/DD and 1.44M DS/HD floppies
+
+    # Avoid computations with some well-known IBM PC floppy formats
+    # Look at: https://en.wikipedia.org/wiki/List_of_floppy_disk_formats#Logical_formats
+    if lba == 640:
+        return (80, 1, 8) # 3.5in DS/DD 320KB
+    elif lba == 720:
+        return (80, 1, 9) # 3.5in DS/DD 360KB
+    elif lba == 1280:
+        return (80, 2, 8) # 3.5in DS/DD 640KB
+    elif lba == 1440:
+        return (80, 2, 9) # 3.5in DS/DD 720KB
+    elif lba == 2880:
+        return (80, 2, 18) # 3.5in DS/HD 1440KB
+    elif lba == 3360:
+        return (80, 2, 21) # 3.5in DS/HD 1680KB (MS-DMF)
+    elif lba == 3440:
+        return (82, 2, 21) # 3.5in DS/HD 1720KB
+    elif lba == 5760:
+        return (80, 2, 36) # 3.5in DS/XD 2880KB
+
+    for hpc in (2,16,32,64,128,255):
         c,h,s = lba2chs(lba,hpc)
         if c < 1024: break
     if DEBUG&1: log("size2chs: calculated Heads Per Cylinder: %d", hpc)

FATtools/version.py

@@ -1 +1 @@
-__version__ = '1.0.11'
+__version__ = '1.0.12'