NAME¶
fdc
—
PC architecture floppy disk controller driver
SYNOPSIS¶
device fdc
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
alternatively
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 disabled 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, device 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 inserting 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 media, 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 digits
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 devices 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 automatically determines these values via the
_FDE and _FDI methods, but this can be overridden by specifying a drive type
hint.
Normally, each configured drive will be probed at initialization time, using a
short seek sequence. This is intended to find out about drives that have been
configured but are actually missing or otherwise 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 include the header file
<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 intended for access to the device without the
requirement to have an accessible 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
operations 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 selected 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 superuser 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 autoselection. 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 argument 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 error” kernel logs for failed I/O
operations.
FDOPT_NOERROR
- Do not indicate I/O errors 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 intended
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 meaning. 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.
Only 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 status, if available. 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 later vastly rewritten by
Jörg Wunsch.