Message-ID: <000601c17097$7b500960$027efea9@atlantis>
From: "Matthias Paul" <Matthias DOT Paul AT post DOT rwth-aachen DOT de>
To: <opendos AT delorie DOT com>
References: <3BF1743E DOT 32E475BE AT 2net DOT co DOT uk>
Subject: Re: Removable compact flash
Date: Fri, 16 Nov 2001 22:09:23 +0100
Organization: University of Technology, RWTH Aachen, Germany
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Reply-To: opendos AT delorie DOT com

On 2001-11-13, Chris Simmonds wrote:

> I have a system with compact flash as my d: drive. From time to time I
> need to take the CF card out and replace it with another one. The
> problem is that DR-DOS thinks it is a hard disk and gives me a disk
> error when I try to access d: after the change.

Chris, unfortunately I have no first-hand experience with compact
flash cards myself and therefore only limited info about them, but
from your description that DR-DOS sees these flash disks as harddisks
I take it that, while most flash cards need a huge stack of drivers
to function, you can use the card without any dedicated drivers as
a normal ATA device, that is, DOS sees the drive through INT 13h
with DL>=80h.

If this would be the case, doesn´t the same happen under, say,
MS-DOS 6.22/7 or PC DOS 2000 as well (just to make sure it´s not
a problem with DR-DOS as is)? Or do you have a so called Enabler
loaded to make use of the card?

INT 13h drives with unit numbers DL>=80h (that is partitioned media)
are logged into the system during the boot phase, and this code is
discarded later, as harddisk are assumed to be non-removeable.
I strongly assume the same occurs with MS-DOS and PC DOS (but
DOS 5.0+ adds three mostly undocumented device driver functions
(47h, 67h, 68h) which are not supported by DR-DOS up to 7.03,
I doubt this will make a difference).

DOS keeps only the code to log in unpartitioned media, that is
floppy disks, at runtime. These are accessed with unit numbers
DL < 80h, and the log-in occurs after a disk change event.
If you would reformat your disk to look as a super-large floppy,
so called "super-floppies" without a MBR, it might be possible
to write a small TSR that sits on top of INT 13h and lets your
flash card look like, for example, floppy drive B:.

Another - dirty - attempt might be flush buffers, patch the
internal drive tables in DOS´ data area to match the geometry
values of the newly inserted card, and then reset the disk
system, so that it works with the new geometry data. (However,
there may be some problems with applications like Windows,
which don´t like harddisks to be changed without a reboot...)

If the flash card is linked into the system not as a harddisk
but as a DOS block device driver (similar to a RAM disk driver),
things should be a bit easier. (If you would have the sources
for that driver it would be almost trivial.)

> I imagine that there is a device driver or other utility that will
> present the CF as a removable media like a floppy disk or zip drive
> and so dr-dos will be happy. Any ideas?

I´m not up to date in regard to latest achievements in flash
technology, so please correct me if I´m wrong.

Such drivers are called Socket Services & Card Services (SS&CS),
in contrast to simply Enablers or no drivers at all. CS are needed
if you want to hot-plug PC Cards or PCMCIA cards, and Stack Services
are needed for CS to run. You will also need a Flash File System (FFS)
driver.
These are/were available from various vendors, including Award´s
DPMS using Cardware (I have some configuration info about 1.01,
2.0, 2.5, and 5.0, but my personal experience is limited to 2.5
from 1995), SystemSoft´s CardWizard, Phoenix Card Manager, or
similar software from Madge, CSM, IBM (have a look at PC DOS 7
or 2000), etc. Various FFSs are available from vendors like Award,
Microsoft, SCM, CSM, Datalight, and others.
Such drivers are often shipped with the corresponding laptops
or PCMCIA/PC Card interfaces, but sometimes they only ship with
Enablers which (usually) allow to drive a single card, which must
not be re-plugged at runtime.

Hope it helps and greets,

 Matthias

PS. It´s good to know you´re still around here! :-)

-- 

 <mailto:Matthias DOT Paul AT post DOT rwth-aachen DOT de>; <mailto:mpaul AT drdos DOT org>
 http://www.uni-bonn.de/~uzs180/mpdokeng.html; http://mpaul.drdos.org