driver itself, then hooking the INT 13h (disk driver) and INT 15h
(memory query) BIOS interrupts.
-To use it, type on the SYSLINUX command line:
+MEMDISK allows for an OS to detect the MEMDISK instance. (See the
+"Additional technical information" section below.)
+
+To use it, type on the Syslinux command line:
memdisk initrd=diskimg.img
a) The disk image can be uncompressed or compressed with gzip or zip.
-b) If the disk image is one of the following sizes, it's assumed to be a
- floppy image:
-
- 368,640 bytes - 360K floppy
- 737,280 bytes - 720K floppy
- 1,222,800 bytes - 1200K floppy
- 1,474,560 bytes - 1440K floppy
- 1,720,320 bytes - 1680K floppy (common extended format)
- 1,763,328 bytes - 1722K floppy (common extended format)
- 2,949,120 bytes - 2880K floppy
- 3,932,160 bytes - 3840K floppy (extended format)
-
- For any other size, the image is assumed to be a hard disk image,
- and should typically have an MBR and a partition table. It may
- optionally have a DOSEMU geometry header; in which case the header
- is used to determine the C/H/S geometry of the disk. Otherwise,
- the geometry is determined by examining the partition table, so the
- entire image should be partitioned for proper operation (it may be
- divided between multiple partitions, however.)
+b) If the disk image is less than 4,194,304 bytes (4096K, 4 MB) it is
+ assumed to be a floppy image and MEMDISK will try to guess its
+ geometry based on the size of the file. MEMDISK recognizes all the
+ standard floppy sizes as well as common extended formats:
+
+ 163,840 bytes (160K) c=40 h=1 s=8 5.25" SSSD
+ 184,320 bytes (180K) c=40 h=1 s=9 5.25" SSSD
+ 327,680 bytes (320K) c=40 h=2 s=8 5.25" DSDD
+ 368,640 bytes (360K) c=40 h=2 s=9 5.25" DSDD
+ 655,360 bytes (640K) c=80 h=2 s=8 3.5" DSDD
+ 737,280 bytes (720K) c=80 h=2 s=9 3.5" DSDD
+ 1,222,800 bytes (1200K) c=80 h=2 s=15 5.25" DSHD
+ 1,474,560 bytes (1440K) c=80 h=2 s=18 3.5" DSHD
+ 1,638,400 bytes (1600K) c=80 h=2 s=20 3.5" DSHD (extended)
+ 1,720,320 bytes (1680K) c=80 h=2 s=21 3.5" DSHD (extended)
+ 1,763,328 bytes (1722K) c=82 h=2 s=21 3.5" DSHD (extended)
+ 1,784,832 bytes (1743K) c=83 h=2 s=21 3.5" DSHD (extended)
+ 1,802,240 bytes (1760K) c=80 h=2 s=22 3.5" DSHD (extended)
+ 1,884,160 bytes (1840K) c=80 h=2 s=23 3.5" DSHD (extended)
+ 1,966,080 bytes (1920K) c=80 h=2 s=24 3.5" DSHD (extended)
+ 2,949,120 bytes (2880K) c=80 h=2 s=36 3.5" DSED
+ 3,194,880 bytes (3120K) c=80 h=2 s=39 3.5" DSED (extended)
+ 3,276,800 bytes (3200K) c=80 h=2 s=40 3.5" DSED (extended)
+ 3,604,480 bytes (3520K) c=80 h=2 s=44 3.5" DSED (extended)
+ 3,932,160 bytes (3840K) c=80 h=2 s=48 3.5" DSED (extended)
+
+ A small perl script is included in the MEMDISK directory which can
+ determine the geometry that MEMDISK would select for other sizes;
+ in general MEMDISK will correctly detect most physical extended
+ formats used, with 80 cylinders or slightly more.
+
+ If the image is 4 MB or larger, it is assumed to be a hard disk
+ image, and should typically have an MBR and a partition table. It
+ may optionally have a DOSEMU geometry header; in which case the
+ header is used to determine the C/H/S geometry of the disk.
+ Otherwise, the geometry is determined by examining the partition
+ table, so the entire image should be partitioned for proper
+ operation (it may be divided between multiple partitions, however.)
You can also specify the geometry manually with the following command
line options:
s=# Specify number of sectors (max 63)
floppy[=#] The image is a floppy image[**]
harddisk[=#] The image is a hard disk image[**]
+ iso The image is an El Torito ISO9660 image (drive 0xE0)
# represents a decimal number.
bigraw Use raw access to protected mode memory, and leave the
CPU in "big real" mode afterwards.
+ int Use plain INT 15h access to protected memory. This assumes
+ that anything which hooks INT 15h knows what it is doing.
+
safeint Use INT 15h access to protected memory, but invoke
INT 15h the way it was *before* MEMDISK was loaded.
+ This is the default since version 3.73.
e) MEMDISK by default supports EDD/EBIOS on hard disks, but not on
floppy disks. This can be controlled with the options:
edd Enable EDD/EBIOS
noedd Disable EDD/EBIOS
+f) The following option can be used to pause to view the messages:
+
+ pause Wait for a keypress right before booting
+
+g) The following option can be used to set the real-mode stack size.
+ The default is 512 bytes, but if there is a failure it might be
+ interesting to set it to something larger:
+
+ stack=size Set the stack to "size" bytes
+
+h) Some systems without a floppy drive have been known to have
+ problems with floppy images. To avoid that those problems, first
+ of all make sure you don't have a floppy drive configured on the
+ BIOS screen. If there is no option to configure that, or that
+ doesn't work, you can use the option:
+
+ nopass Hide all real drives of the same type (floppy or hard disk)
+ nopassany Hide all real drives (floppy and hard disk)
+
Some interesting things to note:
If you're using MEMDISK to boot DOS from a CD-ROM (using ISOLINUX),
you might find the generic El Torito CD-ROM driver by Gary Tong and
-Bart Lagerweij useful:
-
- http://www.nu2.nu/eltorito/
-
+Bart Lagerweij useful. It is now included with the Syslinux
+distribution, in the dosutil directory. See the file
+dosutil/eltorito.txt for more information.
Similarly, if you're booting DOS over the network using PXELINUX, you
can use the "keeppxe" option and use the generic PXE (UNDI) NDIS
The MEMDISK info structure currently contains:
- [ES:DI] word Total size of structure (currently 28 bytes)
+ [ES:DI] word Total size of structure (currently 30 bytes)
[ES:DI+2] byte MEMDISK minor version
[ES:DI+3] byte MEMDISK major version
[ES:DI+4] dword Pointer to MEMDISK data in high memory
- [ES:DI+8] dword Size of MEMDISK data in 512-byte sectors
+ [ES:DI+8] dword Size of MEMDISK data in sectors
[ES:DI+12] 16:16 Far pointer to command line
[ES:DI+16] 16:16 Old INT 13h pointer
[ES:DI+20] 16:16 Old INT 15h pointer
[ES:DI+24] word Amount of DOS memory before MEMDISK loaded
[ES:DI+26] byte Boot loader ID
+ [ES:DI+27] byte Sector size as a power of 2
+ (If zero, assume 512-byte sectors)
+ [ES:DI+28] word If nonzero, offset (vs ES) to installed DPT
+ This pointer+16 contains the original INT 1Eh
+
+Sizes of this structure:
-MEMDISK 3.00 and higher has the size of this structure as 27; earlier
-versions had size 26 and did not include the boot loader ID.
+3.71+ 30 bytes Added DPT pointer
+3.00-3.70 27 bytes Added boot loader ID
+pre-3.00 26 bytes
In addition, the following fields are available at [ES:0]:
The following code can be used to "disable" MEMDISK. Note that it
does not free the handler in DOS memory, and that running this from
-DOS will probably crash your machine (DOS doesn't like drives
-suddenly disappearing from underneath):
+DOS will probably crash your machine (DOS doesn't like drives suddenly
+disappearing from underneath.) This is also not necessarily the best
+method for this.
mov eax, 454D0800h
mov ecx, 444D0000h
mov byte [es:bx], 0EAh ; FAR JMP
mov [es:bx+1], eax
sti
+
+MEMDISK supports the Win9x "safe hook" structure for OS detection.
+(See "Safe Master Boot Record INT 13h Hook Routines," available at
+http://www.osronline.com/ddkx/w98ddk/storage_5l6g.htm as of
+December 7th, 2009.) An OS driver can take a look at the INTerrupt table
+and try to walk along the chain of those hooks that implement the "safe hook"
+structure. For each hook discovered, a vendor can be identified and the OS
+driver can take appropriate action. The OS driver can mark the "flags" field
+of the "safe hook" to indicate that the driver has reviewed it already. This
+prevents accidental re-detection, for example.
+
+MEMDISK adds one additional extension field to the "safe hook" structure, a
+pointer to a special MEMDISK structure called the "mBFT." The mBFT is the
+"MEMDISK Boot Firmware Table" (akin to the iSCSI iBFT and the AoE aBFT). An
+OS driver looking at MEMDISK's "safe hook" should know that this field will
+be present based on the fact that MEMDISK is the vendor identifier.
+
+The mBFT is little more than an ACPI table to prefix MEMDISK's traditional
+MEMDISK info structure (the "MDI"). The ACPI table's details are:
+
+ OEM ID. . . .: MEMDSK
+ OEM Table ID : Syslinux
+
+There is a 1-byte checksum field which covers the length of the mBFT all
+the way through to the end of the MEMDISK info structure.
+
+There is also a physical pointer to the "safe hook" structure associated
+with the MEMDISK instance. An OS driver might use the following logic:
+
+ 1. Walk INT 13h "safe hook" chain as far as possible, marking hooks as
+ having been reviewed. For MEMDISK hooks, the driver then follows the
+ pointer to the mBFT and gathers the RAM disk details from the included
+ MDI.
+ 2. The OS driver scans low memory for valid mBFTs. MEMDISK instances that
+ have been "disconnected" from the INT 13h "safe hook" chain can be thus
+ discovered. Looking at their associated "safe hook" structure will
+ reveal if they were indeed reviewed by the previous stage.
projects / profile / ivi / syslinux.git / blobdiff