fdrawcmd - send raw commands to the floppy disk controller
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fdrawcmd [drive=drive] [rate=rate]
[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 drive.
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
Selects the drive. The default is drive 0 (‘/dev/fd0’).
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
Describes the length of the transferred data for commands
reading from and writing to the disk. The default is to
continue until end of file.
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 command
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 need
mode Various flags or’ed together describing the properties of the
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
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.
Commands available on all FDCs
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.
Returns the third status byte (ST3)
Recalibrates the drive and returns ST0 ST1.
seek drvsel cyl
Moves the head to cyl and returns ST0 ST1.
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.
reads the first sector header that comes and returns ST0 ST1 ST2
and cyl head sect szcod of the encountered header.
Commands available on 82072 and later
Prints the contents of the FDCs registers, if supported.
Commands available on 82072A and later
configure conf1 conf2 conf3
Configures FIFO operation.
Commands available on 82077 and later
Echoes 0x90 if the FDC is more recent than 82072A, and 0x80
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 0.
seek_in drvsel n
does a relative seek of n cylinders away from cylinder 0.
Commands available on 82077AA and later
lock Locks the FIFO configuration, so that it survives a FDC software
Unlock the FIFO configuration
Commands available on 82078
echoes a byte describing the type of the FDC in the 3 high bits,
and the stepping in the three low bits.
configures automatic power down of the FDC. The old
configuration is echoed
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
save 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 og 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
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 otherwise.
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
If on the other hand you give a command name preceded by explicit
modes, only the explicit modes are or’ed together.
read Read data from disk using DMA.
write Write data to the disk.
intr Wait for an interrupt.
spin wait for the disk to spin up
disk 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 command
Switch off the motor immediately after the command returns.
fm Uses the FM version of the read, readid, write and format
no-mt 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 sect-per-track.
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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