Looking for a simple write-only file system

From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2003-06-19 10:31:50

Good news everyone: the prototype of the combined 32 kB SRAM and 4 MB Flash ROM
cartridge for the VIC-20 works.  In principle, it's the same design that we
already had two years ago, but there have been various practical problems.
This prototype uses three chips: 62256 SRAM, Am29F032B flash and Lattice 1016
programmable logic.

The menu software I wrote over two years ago supports one directory only.
I thought that it'd be nice to have subdirectories, since it is a bit hard
to keep track of 4 megabytes of compressed data.  I have an idea how the
subdirectories could be implemented without wasting a lot of space, but I'd
also look for existing solutions.

The Am29F032B has 64-kilobyte sectors, but I wouldn't be making use of the
"sector erase" feature.  With a 38,400 bps C2N232 connection, the entire
flash can be reprogrammed in less than 20 minutes.

I'd interleave the directory entries with the data (like in the archiving
programs lha and tar) and provide each entry with links to the next and
previous entry.  The data would be aligned on a byte boundary.  The last
entry would have a link $ffffff, so that new files can be appended without
reprogramming the entire flash.  Also files could be deleted by programming
some "file type" bits to all zero.

Does anyone have some write-only file system code that I could use?  I'm
going to release the design and all program code under the GNU General
Public License.  Assembled and tested devices will hopefully be available
by September or October for 50 to 60 EUR a piece.


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