At 03:45 PM 12/29/2007, you wrote:

>On Fri, 2007-12-28 at 20:10 -0800, Vasile Surducan wrote:
> > On 12/28/07, Herbert Graf <mailinglist4@farcite.net> wrote:
> > >
> > > On Fri, 2007-12-28 at 12:06 -0800, Rob Susmilch wrote:
> > > > Hello everyone,
> > > >
> > > > First some background. I'm going to be building a simple stand
> > alone data
> > > > logger for personal use (and the fun of creating it of course)
> > since most stand
> > > > alone loggers are hundreds of dollars. I will most likely be using
> > a pic18f4553
> > > > IIRC, and either interfacing to a ADC chip or using the on-board
> > A/D. I also am
> > > > going to be interfacing to SD card since from what I've read they
> > are easy to
> > > > do.
> > > >
> > > > My question is, and I've searched high and low, how to implement
> > compression on
> > > > this little bugger. Granted I suppose getting a jumbo SD card
> > could negate any
> > > > compression done, but I may perhaps go to a simple serial EEPROM
> > instead. All
> > >
> > > Frankly, once you get the init done, an SD card in SPI mode is not
> > > really much more complicated to use then a serial EEPROM.
> >
> > If you don't implement the FAT. Else...
>
>You don't have to do any FAT stuff. For example, my carmon project
>doesn't even use the FAT:
>
>http://repatch.dyndns.org:8383/pic_stuff/carmon
>
>Once you have the actual sector that the file you want to write to
>starts, you don't have to worry anymore about FS stuff if you set things
>up correctly.
>
>In my case, I simply write a file to the flash card (in my case a CF
>card, I've done the same with an SD card, I can post that code if anyone
>is interested) with a computer that fills the whole card. The file
>contains all zeros.
>
>The PIC simply scans the file, finds the first sector that doesn't have
>zeros, and continues writing.
>
>On the PC side I simply scan the file for all non zero data.
>
>The only limitation to this method is you can't write zero to the file,
>usually not an issue (I just write all ASCII).
>
>The "init" portion consists of reading the partition table (one sector,
>fixed location), reading the boot sector of the first partition (to find
>the location of the root directory) and then scanning the root directory
>for your file.
>
>It all sounds more complicated then it really is. The actually "writing"
>code simply keeps track of how close to the end of the card I am, and
>what sector I want to write to next, barely more complicated then
>writing to an EEPROM.
>
>TTYL
>--

Hi, Herbert:-

I'd be interested in seeing the SD card code. Will it work with the
newer cards with larger sector sizes?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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