fdc(4)

NAME

fdc - PC architecture floppy disk controller driver

SYNOPSIS

device fdc
device fd
In /boot/device.hints:
hint.fdc.0.at="isa"
hint.fdc.0.port="0x3F0"
hint.fdc.0.irq="6"
hint.fdc.0.drq="2"
hint.fdc.0.flags="0x0"
hint.fd.0.at="fdc0"
hint.fd.0.drive="0"
hint.fd.0.flags="0x0"
hint.fd.1.at="fdc0"
hint.fd.1.drive="1"
hint.fd.1.flags="0x0"

DESCRIPTION

Device Usage

This driver provides access to floppy disk drives. Floppy

disks using
either FM (single-density) or MFM (double or high-density)

recording can
be handled.

Floppy disk controllers can connect up to four drives each.

The fdc
driver can currently handle up to two drives per controller

(or four
drives on ACPI). Upon driver initialization, an attempt is

made to find
out the type of the floppy controller in use. The known

controller types
are either the original NE765 or i8272 chips, or alterna

tively enhanced
controllers that are compatible with the NE72065 or i82077

chips. These
enhanced controllers (among other enhancements) implement a

FIFO for
floppy data transfers that will automatically be enabled

once an enhanced
chip has been detected. This FIFO activation can be dis

abled using the
per-controller flags value of 0x1.

By default, this driver creates a single device node

/dev/fdN for each
attached drive with number N. For historical reasons, de

vice nodes that
use a trailing UFS-style partition letter (ranging from `a'

through `h')
can also be accessed, which will be implemented as symbolic

links to the
main device node.

Accessing the main device node will attempt to autodetect

the density of
the available medium for multi-density devices. Thus it is

possible to
use either a 720 KB medium or a 1440 KB medium in a high

density 3.5 inch
standard floppy drive. Normally, this autodetection will

only happen
once at the first call to open(2) for the device after in

serting the
medium. This assumes the drive offers proper changeline

support so media
changes can be detected by the driver. To indicate a drive

that does not
have the changeline support, this can be overridden using

the per-drive
device flags value of 0x10 (causing each call to open(2) to

perform the
autodetection).

When trying to use a floppy device with special-density me

dia, other
device nodes can be created, of the form /dev/fdN.MMMM,

where N is the
drive number, and MMMM is a number between one and four dig

its describing
the device density. Up to 15 additional subdevices per

drive can be created that way. The administrator is free to decide on a

policy how to
assign these numbers. The two common policies are to either

implement
subdevices numbered 1 through 15, or to use a number that

describes the
medium density in kilobytes. Initially, each of those de

vices will be
configured to the maximal density that is possible for the

drive type
(like 1200 KB for 5.25 inch HD drives or 1440 KB for 3.5

inch HD drives).
The desired density to be used on that subdevice needs to be

configured
using fdcontrol(8).

Drive types are configured using the lower four bits of the

per-drive
device flags. The following values can be specified:

1 5.25 inch double-density device with 40 cylinders

(360 KB

native capacity)

2 5.25 inch high-density device with 80 cylinders

(1200 KB native

capacity)

3 3.5 inch double-density device with 80 cylinders

(720 KB native

capacity)

4 3.5 inch high-density device with 80 cylinders

(1440 KB native

capacity)

5 3.5 inch extra-density device with 80 cylinders

(2880 KB native

capacity, usage currently restricted to at most

1440 KB media)

6 Same as type 5, available for compatibility with

some BIOSes

On IA32 architectures, the drive type can be specified as 0

for the
drives. In that case, the CMOS configuration memory will be

consulted to
obtain the value for that drive. The ACPI probe automati

cally determines
these values via the _FDE and _FDI methods, but this can be

overriden by
specifying a drive type hint.

Normally, each configured drive will be probed at initial

ization time,
using a short seek sequence. This is intended to find out

about drives
that have been configured but are actually missing or other

wise not
responding. (The ACPI probe method does not perform this

seek.) In some
environments (like laptops with detachable drives), it might

be desirable
to bypass this drive probe, and pretend a drive to be there

so the driver
autoconfiguration will work even if the drive is currently

not present.
For that purpose, a per-drive device flags value of 0x20

needs to be
specified.

Programming Interface

In addition to the normal read and write functionality, the

fdc driver
offers a number of configurable options using ioctl(2). In

order to
access any of this functionality, programmers need to in

clude the header
file #include <sys/fdcio.h>
into their programs. The call to open(2) can be performed

in two possible ways. When opening the device without the O_NONBLOCK

flag set, the
device is opened in a normal way, which would cause the main

device nodes
to perform automatic media density selection, and which will

yield a file
descriptor that is fully available for any I/O operation or

any of the
following ioctl(2) commands.

When opening the device with O_NONBLOCK set, automatic media

density
selection will be bypassed, and the device remains in a

half-opened
state. No actual I/O operations are possible, but many of

the ioctl(2)
commands described below can be performed. This mode is in

tended for
access to the device without the requirement to have an ac

cessible media
present, like for status inquiries to the drive, or in order

to format a
medium. O_NONBLOCK needs to be cleared before I/O opera

tions are possible on the descriptor, which requires a prior specification

of the density using the FD_STYPE command (see below). Operations

that are not
allowed on the half-opened descriptor will cause an error

value of
EAGAIN.

The following ioctl(2) commands are currently available:

FD_FORM Used to format a floppy disk medium. Third

argument is a

pointer to a struct fd_formb specifying which

track to
format, and which parameters to fill into the

ID fields of
the floppy disk medium.

FD_GTYPE Returns the current density definition record

for the

selected device. Third argument is a pointer

to struct
fd_type.

FD_STYPE Adjusts the density definition of the select

ed device.

Third argument is a pointer to struct

fd_type. For the
fixed-density subdevices (1 through 15 per

drive), this
operation is restricted to a process with su

peruser privileges. For the auto-selecting subdevice 0,

the operation
is temporarily allowed to any process, but

this setting
will be lost again upon the next autoselec

tion. This can
be used when formatting a new medium (which

will require
to open the device using O_NONBLOCK, and thus

to later
adjust the density using FD_STYPE).

FD_GOPTS Obtain the current drive options. Third ar

gument is a

pointer to int, containing a bitwise union of

the following possible flag values:

FDOPT_NORETRY Do not automatically

retry operations

upon failure.

FDOPT_NOERRLOG Do not cause ``hard er

ror'' kernel

logs for failed I/O oper

ations.

FDOPT_NOERROR Do not indicate I/O er

rors when

returning from read(2) or

write(2)
system calls. The caller

is assumed
to use FD_GSTAT calls in

order to
inquire about the success

of each
operation. This is in

tended to allow
even erroneous data from

bad blocks to
be retrieved using normal

I/O operations.

FDOPT_AUTOSEL Device performs automatic

density

selection. Unlike the

above flags,
this one is read-only.

FD_SOPTS Set device options, see above for their mean

ing. Third

argument is a pointer to int. Drive options

will always
be cleared when closing the descriptor.

FD_DEBUG Set the driver debug level. Third argument

is a pointer

to int, level 0 turns off all debugging. On

ly applicable
if the driver has been configured with

options FDC_DEBUG.

FD_CLRERR Clear the internal low-level error counter.

Normally,

controller-level I/O errors are only logged

up to
FDC_ERRMAX errors (currently defined to 100).

This command resets the counter. Requires superuser

privileges.

FD_READID Read one sector ID field from the floppy disk

medium.

Third argument is a pointer to struct

fdc_readid, where
the read data will be returned. Can be used

to analyze a
floppy disk medium.

FD_GSTAT Return the recent floppy disk controller sta

tus, if avail

able. Third argument is a pointer to struct

fdc_status,
where the status registers (ST0, ST1, ST2, C,

H, R, and N)
are being returned. EINVAL will be caused if

no recent
status is available.

FD_GDTYPE Returns the floppy disk drive type. Third

argument is a

pointer to enum fd_drivetype. This type is

the same as
being used in the per-drive configuration

flags, or in the
CMOS configuration data or ACPI namespace on

IA32 systems.

FILES

/dev/fd* floppy disk device nodes

SEE ALSO

fdformat(1), fdread(1), fdwrite(1), ioctl(2), open(2),

read(2), write(2),
fdcontrol(8)

AUTHORS

This man page was initially written by Wilko Bulte, and lat

er vastly
rewritten by Jorg Wunsch.

BSD July 15, 2004

BSD