CONTENTS

SYNOPSIS

DESCRIPTION

Commands are implemented to query the current device density settings as well as the underlying device hardware as registered with the driver, to manipulate debugging levels, and to adjust the device density settings. All the operations that manipulate the kernel settings are restricted to the superuser (by the device driver), while all inquiry requests only require read access to device.

In order to add some descriptive text that makes the output better human readable, the flag -v can be added.

Density Control

The second form to specify a device density uses -s fmtstr to explicitly specify each parameter in detail. The argument fmtstr is a comma-separated list of values of the form:

.Sm off sectrac, secsize, datalen, gap, ncyls, speed, heads, f_gap, f_inter, offs2, flags
.Sm on

The meaning of the parameters is:

sectrac	The number of sectors per track.
secsize	The sector size code, 0 = 128 bytes (or less), 1 = 256 bytes, 2 = 512 bytes, 3 = 1024 bytes.
datalen	The actual sector size if the size code is 0, or the (ignored) value 0xFF for larger size codes.
gap	The length of the gap 3 parameter for read/write operations.
ncyls	The number of cylinders.
speed	The transfer speed in kilobytes per second. Can be 250, 300, 500, or 1000, but each drive type only supports a subset of these values.
heads	The number of heads.
f_gap	The length of the gap 3 when formatting media.
f_inter	The sector interleave to be applied when formatting. 0 means no interleave, 1 means 1:1 etc.
offs2	The offset of the sector numbers on side 2 (i.e., head number 1). Normally, sector numbering on both sides starts with 1.
flags	A list from one of the following flag values:

+mfm	Use MFM encoding.
-mfm	Use FM (single-density) encoding.
+2step	Use 2 steps per each cylinder (for accessing 40-cylinder media in 80-cylinder drives).
-2step	Do not use 2 steps per cylinder, i.e., access each physical cylinder of the drive.
+perpend	Use perpendicular recording (for 2.88 MB media, currently not supported).
-perpend	Use longitudinal recording.

Same as above, but with verbose output. Note that the result is about the "drive type", as opposed to a "device density", so it is independent from the actual subdevice being used for device.
$ fdcontrol -v /dev/fd0
/dev/fd0: 1.44M drive (3.5" high-density)

Inquiry about the density settings:
$ fdcontrol -F /dev/fd0
18,512,0xff,0x1b,80,500,2,0x6c,1,0,+mfm

The verbose flag makes this human readable:
/dev/fd0: 1440 KB media type
Format: 18,512,0xff,0x1b,80,500,2,0x6c,1,0,+mfm
Sector size: 512
Sectors/track: 18
Heads/cylinder: 2
Cylinders/disk: 80
Transfer rate: 500 kbps
Sector gap:27
Format gap:108
Interleave:1
Side offset: 0
Flags <MFM>

As indicated, trailing commas in the parameter list may be omitted.

In order to access archaic 160 KB single-density (FM encoded) 5.25 media in a modern 1.2M drive, something like the following definition would be needed. (Note that not all controller hardware is actually capable of handling FM encoding at all.)
# fdcontrol -s 16,128,0x80,0x2,40,300,,0x10,,,-mfm,+2step /dev/fd1.1

HISTORY

AUTHORS