fdrawcmd - send raw commands to the floppy disk controller
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fdrawcmd [drive= drive] [rate=rate]
[length= length] [repeat=repeat]
[cylinder= physical-cyl] command [parameters ...] [mode]
fdrawcmd is used to send raw commands to the floppy disk controller, after
having selected a given drive. You must have write permission to the selected
When writing to a disk, data is read from stdin; when reading, data is printed
to stdout. Diagnostic messages, return values from the controller, and the
value of the disk change line after the command are printed to stderr.
All numbers may be given in octal (0211), decimal (137), or hexadecimal (0x89).
- Selects the drive. The default is drive 0
- Selects the data transfer rate. Use 0 for high density
disks, 1 for double density 5 1/4 disks (or 2 Mbps tapes, if the
appropriate rate table is selected), and 2 for double density 3 1/2
- Describes the length of the transferred data for commands
reading from and writing to the disk. The default is to continue until end
- Repeat the command count times. This only works
correctly for commands which don't do any data transfer.
- Seek to the given cylinder before executing the
- The name of the command to send. command may be a
spelled out name (like read or write), or a number representing the
commands floppy disk controller opcode. A named command has already a mode
associated with it, whereas for a number the mode parameter should be
described using the mode option.
- The parameters for the command (optional, not all commands
- Various flags or'ed together describing the properties of
The description of the various floppy commands given in this manpage is very
sketchy. For more details get the 82078 spec sheet which can be found at:
Look for the chapter COMMAND SET/DESCRIPTIONS. Older FDCs only support a subset
of the commands described therein, but the syntax for the commands that do
exist is the same.
- read drvsel cyl head sect szcod spt rw-gap szcod2
- Reads length bytes of data from the disk.
drvsel is the drive selector. Bit 0 and 1 describe the drive, and
bit 2 describes the head. The remaining parameters give the cylinder, head
(yes, again), sector, size of the sector (128 * 2 ^ szcod), sectors
per track (spt, this is used to switch to the second head when the first
side has been read), and size of the read-write gap. szcod2 should
be 0xff. read returns ST0 ST1 ST2 and cyl head sect
szcod of the next sector to be read; see
- N.B. Certain newer floppy disk controllers are buggy, and
do not correctly recognize the end of transfer when operating in virtual
DMA mode. For these, you need to set spt to the id of the last sector to
be read (for example, if you intend to read sectors 2, 3, 4, set spt to 4,
even if the disk has more sectors), and set the no-mt flag.
- write drvsel cyl head sect szcod spt rw-gap szcod2
- Analogous to read.
- sense drvsel
- Returns the third status byte (ST3)
- recalibrate drvsel
- Recalibrates the drive and returns ST0 ST1.
- seek drvsel cyl
- Moves the head to cyl and returns ST0
- specify drvsel spec1 spec2
- Specify various parameters to the drive.
- format drvsel szcod sect-per-track fmt-gap fmt-fill
- Formats the cylinder. The new sectors are filled with
fmt-fill. The header information comes from the input, which is
made up of cyl head sect szcod quadruples. The szcod
parameter from the command line is used to describe the actual size of the
sectors, and the szcod from the input is used to write into the
header. However, the first write to these sectors will use the header
information, and might overwrite the following sectors if the szcod
parameter from the command line was too small.
- readid drvsel
- reads the first sector header that comes and returns ST0
ST1 ST2 and cyl head sect szcod of the encountered
- Prints the contents of the FDCs registers, if
- configure conf1 conf2 conf3
- Configures FIFO operation.
- Echoes 0x90 if the FDC is more recent than 82072A, and 0x80
- perpendicular rate
- Sets the perpendicular mode. Use 0 for normal, 2 for
500kb/s perpendicular, and 3 for 1 Mb/s perpendicular.
- seek_out drvsel n
- does a relative seek of n cylinders towards cylinder
- seek_in drvsel n
- does a relative seek of n cylinders away from
- Locks the FIFO configuration, so that it survives a FDC
- Unlock the FIFO configuration
- echoes a byte describing the type of the FDC in the 3 high
bits, and the stepping in the three low bits.
- powerdown powerconf
- configures automatic power down of the FDC. The old
configuration is echoed
- option iso
- enables/disables ISO formats. Odd values of iso
enable these formats, whereas even values disable them. ISO formats don't
have index headers, and thus allow to fit slightly more data on a
- prints out 16 internal registers of the FDC.
- restore r1 r2 r3 ... r16
- restores the 16 internal registers of the FDC.
- format_n_write drvsel szcod sect-per-track fmt-gap fmt-fill
- formats the cylinder and writes initial data to it. The
input data is made up of a sequence of headers (4 bytes) and data:
header1 data1 header2 data2 ... headern datan
- drivespec dspec1 dspec2 ... specn terminator
- chooses rate tables for various drives. Each dspec byte
describes one drive. Bits 0 and 1 say which drive is described. Bits 2 and
3 describe the rate table. Only tables 0 and 2 are interesting. Both
tables only differ in the meaning of rate 1. For table 0 (the default)
rate 0 is 300 kb/s (used for 5 1/4 DD disks), whereas for table 1 it is 2
Mbps (used for fast floppy tape drives). Bit 4 is the precompensation
table select bit. It should be set to 0. Bit 5-7 should be zero as well.
The terminator byte ends the drivespec command. It is either 0xc0
or 0x80. If it is 0xc0, no result phase follows; if it is 0x80, the
current data rate table configuration for the four drives is echoed.
The mode option is only needed when you describe the command as a numerical
value. Some mode names are also valid command names. They are considered as
command name if the command name has not yet been given, and as mode name
If you give a command name followed by explicit modes, both the implicit flags
of the command name, and the explicit modes are or'ed together.
If on the other hand you give a command name preceded by explicit modes, only
the explicit modes are or'ed together.
- Read data from disk using DMA.
- Write data to the disk.
- Wait for an interrupt.
- wait for the disk to spin up
- Aborts the operation if no disk is in the drive. This only
works if you also chose a physical cylinder to seek to.
- Don't switch on the drive motor while issuing the
- Switch off the motor immediately after the command
- Uses the FM version of the read, readid, write and format
- Do not use MT (multitrack) mode for the read, readid and
write commands. This is needed on certain broken FDC's which don't
recognize end of transfer when running in nodma mode. In order to use
these safely, set no-mt, and chose the id of the last sector to be read as
fdrawcmd opens the device node with the NDELAY flag. This means that the driver
should not try to autodetect the disk type (it might not be formatted), and
that it should not reset the FDC. If a reset was needed, the command simply
fails. If that happens, execute floppycontrol --resetnow 0 , and try again.
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