interfacing USB flash disk

I am designing a microcontroller based device which needs to connect to 
PC, probably by USB, and also needs some removable storage.

My first thought was to use compact flash for the storage because I've 
done that before & know how to use it. But then I wondered about using 
the USB flash disks you can get (the pen-type things built into a USB 
plug). I presume the problem with this would be (A) my device would have 
to be a USB host which adds a lot of complication and (B) getting the 
information on how to communicate with the flash disk. Has anyone tried 
to do this?
-- 
Tim Mitchell

> My first thought was to use compact flash for the storage because I've
> done that before & know how to use it. But then I wondered about using
> the USB flash disks you can get (the pen-type things built into a USB
> plug). I presume the problem with this would be (A) my device would have
> to be a USB host which adds a lot of complication and (B) getting the
> information on how to communicate with the flash disk. Has anyone tried
> to do this?

Yes, you would have to be a host to drive one of these USB flash discs. You
would also have to implement the host portion of the Mass Storage device
class in your system (the specifications for which is downloadable from
www.usb.org). It would be easier to use a CF card (SD/MMC/etc.) as your
storage media. I've not tried the USB-flash disc route myself (preferred CF
card!).

    Andrew

Tim Mitchell wrote:
> I am designing a microcontroller based device which needs to connect to 
> PC, probably by USB, and also needs some removable storage.

As I think you know, when connected to the PC, your device
would need to be a USB "device." When connecting to the
removable storage, your device would need to be a USB host.

> My first thought was to use compact flash for the storage because I've 
> done that before & know how to use it. But then I wondered about using 
> the USB flash disks you can get (the pen-type things built into a USB 
> plug). I presume the problem with this would be 
> (A) my device would have to be a USB host which adds a lot of complication and 

Yep. You need a USB host-controller, and a USB software stack
(non-trivial).

> (B) getting the information on how to communicate with the flash disk. 

The USB mass storage specification is your starting point
for this.

> Has anyone tried to do this?

I have written an OHCI USB host controller framework, that
supports control, bulk, and interrupt transfers (no isochronous
support yet.)

On top of this, I have written a USB mass storage bulk-only
driver. This amounts to running SCSI commands using the USB
Transparent Transport mechanism, over bulk-in and bulk-out
pipes.

However, I have found that there are *many* non-standard
behaviors associated with different devices :-(
Different devices support different sub-sets of SCSI
commands.

After that, I have FAT16 running over a block device
driver adapter.

All of my code is written in C++ running under an RTOS.
The current implementation is running on a powerpc 860
class board.

If you don't need the RTOS and have plenty of resources,
you can always run Linux, and use their USB mass storage
support without so much pain ;-)


-- 
Michael N. Moran           (h) 770 516 7918
5009 Old Field Ct.         (c) 678 521 5460
Kennesaw, GA, USA 30144

"... abstractions save us time working, but they don't
  save us time learning."
Joel Spolsky, The Law of Leaky Abstractions

The Beatles were wrong: 1 & 1 & 1 is 1

> done that before & know how to use it. But then I wondered about using 
> the USB flash disks you can get (the pen-type things built into a USB 
> plug). I presume the problem with this would be (A) my device would have 
> to be a USB host which adds a lot of complication and (B) getting the 
> information on how to communicate with the flash disk. Has anyone tried 

This problem is actually not as intractable as it sounds (for small
values of "not difficult" - anything involving USB is inherently more
difficult than it ought to be, partly because USB is evil, and partly
because vendors of USB hardware only test their products with Windows,
if at all, and frequently assume the existence and/or rely upon the
presence of Microsoft-specific implementation noncompliance).

The hostishness problem can be solved with an embedded USB host
controller. Faced with a similar problem recently, I selected the
Cypress SL811HS. This is available in a 28-pin PLCC (or 48-pin TQFP)
package and is mechanically easy to prototype. It can function as
either a host or a peripheral. It's about $8.50 in qty 1 (price goes
down rapidly with quantity) and readily available. There are other
options too.

The communication problem is "simple" in that there is a vanilla
storage device class, which those pen disks implement. That is why
they don't require drivers when used with Windows Me, 2000 or XP, all
of which include a driver for the generic storage class.

You might want to consider AT45DBCxxx Dataflash cards.
SPI interface, well documented in the datflash datasheets
and low cost.
Only drawback is that the size is currently limited to 8 MBytes.


-- 
Best Regards,
Ulf Samuelsson   ulf@a-t-m-e-l.com
This is a personal view which may or may not be
share by my Employer Atmel Nordic AB


"Tim Mitchell" <timng@sabretechnology.co.uk> skrev i meddelandet
news:PgEKhQVANCYAFAJH@tega.co.uk...
> I am designing a microcontroller based device which needs to connect to
> PC, probably by USB, and also needs some removable storage.
>
> My first thought was to use compact flash for the storage because I've
> done that before & know how to use it. But then I wondered about using
> the USB flash disks you can get (the pen-type things built into a USB
> plug). I presume the problem with this would be (A) my device would have
> to be a USB host which adds a lot of complication and (B) getting the
> information on how to communicate with the flash disk. Has anyone tried
> to do this?
> -- 
> Tim Mitchell

I'm finishing a project that uses the AT89C51SND1 chip.  The dev kit comes
with source code, board, etc as an MP3 player that uses USB and Windows Mass
Storage Device Driver.  It also comes with documenatation on how to hook it
to a CompactFlash card.  I suggest this chip.

Sean


"Tim Mitchell" <timng@sabretechnology.co.uk> wrote in message
news:PgEKhQVANCYAFAJH@tega.co.uk...
> I am designing a microcontroller based device which needs to connect to
> PC, probably by USB, and also needs some removable storage.
>
> My first thought was to use compact flash for the storage because I've
> done that before & know how to use it. But then I wondered about using
> the USB flash disks you can get (the pen-type things built into a USB
> plug). I presume the problem with this would be (A) my device would have
> to be a USB host which adds a lot of complication and (B) getting the
> information on how to communicate with the flash disk. Has anyone tried
> to do this?
> -- 
> Tim Mitchell

does anyone know of a  USB master for embedded use ??

hamilton wrote:
> 
> does anyone know of a  USB master for embedded use ??
> 

i.e. Philips ISP1362 and much time to write an USB host firmware stack. 
There are a few companies offers more or less suitable stacks for 
several platforms...

Steffen
-- 
http://www.da0hq.de

> You might want to consider AT45DBCxxx Dataflash cards.
> SPI interface, well documented in the datflash datasheets
> and low cost.
> Only drawback is that the size is currently limited to 8 MBytes.

I came to the same conclusion. Running a USB host on a 'real' embedded
system (8 & 16 bit) is non-trivial.

Interfacing to Compactflash can be done. Sandisk has got some
application notes on the topic:
http://www.sandisk.com/oem_application_notes.html

Using SD/MMC SPI compatible devices seems to be the simplest solution.
My only problem is that they are a bit to small for my application
(industrial equipment). Having a small card sounds great for a cell
phone. But not so great when you are working in a heavy industry.

Thus anyone know of any other (SPI comp.) form factor ? 

I haven' looked yet, but any suggestions for SD/MMC connectors ?

I was also wondering what happens if you take out the card, is it
directly interfaced to the uP or is there some power-off sequence to
follow ?

Stijn

These comments are intended to be my own opinion and they
may, or may not be shared by my employer, Atmel Sweden.

"hamilton" <hamilton@deminsional.com> wrote in message
news:40625fe3_3@omega.dimensional.com...
>
> does anyone know of a  USB master for embedded use ??


Check out the AT43USB370/380...
Includes a CPU with the USB Stack.
The main CPU needs a library for the different device classes.
Currently Mass Storage is available and Printer in the works.

-- 
Best Regards
Ulf at atmel dot com