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Re: IDE-Harddiskdriver for MCUs
>>>>> "joel" == joel <joel@OARcorp.com> writes:
joel> On Fri, 4 Jun 1999, Robert J. Brown wrote:
>> I implemented a diskless filesystem last year for a project for
>> a client. I did not have to write persistent data to the
>> filesystem -- only temporary data. I also had the ability to
>> pre-load constant files at system build time. The application
>> was an embedded webserver with CGI capability. We talked about
>> adding tha ability to write flash at runtime, but there are
>> timing issues and interrupt latency problems when you do that,
>> and we might have missed an interrupt her or there. :-(
joel> One of the RTEMS uses has used the TFTP client filesystem to
joel> download a tar image of the initial filesystem contents for
joel> his RTEMS based web server. :)
joel> Your setup sounds very similar to the RTEMS In-Memory File
joel> System (IMFS). Our functionality goal for the IMFS may have
joel> been a bit higher though since one of its primary purposes
joel> was to fully exercise the filesystem infrastructure and
joel> POSIX 1003.1b functionality. So it supports regular files,
joel> device files, directories (readdir family), symbolic links,
joel> permissions, etc.. We needed a filesystem that was easy to
joel> test the entire set of system calls with and IMFS was the
joel> result.
My diskless filesystem was just as minimal as I could get and still
get the webserver to run. I supported filenames with "/" in them like
any other character instead of a nested directory structure. It was
good enough to make the webserver work. I only supported open for
read, open for write, delete, and filesize operations, as that was all
I needed for the task at hand.
Because memory was tight (isn't it always?), I used a psuedo-sector
pool and allocated sectors as needed to grow the file size. I kept
directory entries in their own seperate structure because it was
simpler that way. Number-of-sectors and bytes-per-sector were
parameters that were tunable at build time, so once you knew the sizes
of the canned files and the amount of free space, you could optimize
the space requirements pretty well.
joel> The other filesystem at this point is a TFTP client where
joel> /MNT_POINT/TFTP_SERVER/PATH_ON_TFTP_SERVER is the style of
joel> the names in that filesystem namespace.
--
-------- "And there came a writing to him from Elijah" [2Ch 21:12] --------
R. J. Brown III rj@elilabs.com http://www.elilabs.com/~rj voice 847 543-4060
Elijah Laboratories Inc. 457 Signal Lane, Grayslake IL 60030 fax 847 543-4061
----- M o d e l i n g t h e M e t h o d s o f t h e M i n d ------
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