[comp.sys.3b1] Direct access to floppy

minear@sctc.com (Spence Minear) (05/20/91)

I would like to get a program that would allow me read and write disk
blocks directly to and from the floppy disk.  I need to exchange some
data with other machines and find that the 3b1's GD driver is a bit
picky on what it finds on the disk.

I have been experimenting trying to use the ioctl calls as documented
in the GD(7) man page in the User Manual Vol. 1.  The problem is I
don't know what the options for the XXXXX filds of the commands to the
2729 are.  I do know that using 0 for all of them on a read will cause
the system to panic.

If some one has a simple example program, and/or some documentation on
what the 'x' fields mean and what values can be used for the various
commands supported by GD I would appreciate any help you can provide.

From observation it seems to me that the GD driver as used by any
normal system command insists on finding a struture on block 0 left by
iv when the disk is formated.  If GD can't find this information it
refuses to set the values to some reasonable defaults and try to let
you read the block anyway.  For example if a disk is formated but does
not have the right structure on block zero then the dd and tar
commands fail because GD refuses to set defaults and let you read
blocks anyway.  Does anyone know if this observation is close to what
is going on?

Any and all responses to minear@sctc.com will be appreciated.

-- sem (Spence Minear)
A check on what I think is happening would also be apprecieated.  (So
what do I think is