I'm curious. Is anyone worrying about connecting a disk drive (floppy or HD) to an embedded system evaluation board? Or is the general approach to just use the Ethernet connection to a host? I've got a few evaluation systems (EZ80, Rabbit, PowerPC, 68332) and I'd like to try providing them with their own, decicated bulk storage. I've looked at USB, but the protocol seems horribly complex.
Or do folks just use flash RAM?
Jack
Smartmedia cards are probably the easiest as they have a SPI type interface. Forget floppies - too fiddly and not enough capacity.
Both ATAPI (IDE) hard disks and compact flash cards use essentially the same fairly simple interface which many people have managed to connect to various microcontrollers - I had one running with a processor hosted in an FPGA for a while. If you only have an 8-bit bus you will probably need something to get at the high half of the data lines, but that shouldn't be too complicated. If you don't need to be compatible with anything else, you can also only use the low 8 data lines and loose half the disk capacity by only utilizing every other byte.
A drive recent enough to support logical block addressing is pretty much just a sea of sectors - you don't absolutely have to implement a file system if you have another storage organization scheme, although you may want to. One common solution is a degenerate FAT file system - readable by a pc, but only writeable by your device as you make simplify assumptions about where everything goes which an operating system FAT driver will not honor (some digital cameras are like this - if you write to the card in a PC, you have to reformat it before the camera can use it again). Also, if you use a custom storage scheme, a PC operating system like linux which allows you to access a physical drive as if it were a file will let you write pc-software to interact with your custom storage format, without having to have an OS driver capable of understanding it.
There are SPI-USB modules available. We are actually exporing such an option right now on an application. There are also SPI to CF modules available.
Depends on specifics of your application and/or budget.
JW
Are these USB master or USB slave ??
THE Jack Crenshaw?
If so, I've got your MATH Toolkit for RT Programming Book. Nice work.
Anyways, check out Atmel's archives for their Applications Journal, Issue 2 - Spring 2004. "Construct an ATA Hard Drive Controller". Here's a link;
The archive is here;
Hope that helps...
- Richard
We normally use Ethernet - it helps that our TCP/IP stack is fairly small. We have prototyped a USB interface to memory sticks using one of the Cypress chips, but found that we could only fit the sector read/write routines into the Cypresss chip internal RAM, and that only after serious hacking of the code supplied by Cypress.
Stephen
-- Stephen Pelc, snipped-for-privacy@INVALID.mpeltd.demon.co.uk MicroProcessor Engineering Ltd - More Real, Less Time
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