#FAST_FAT on fat.h file

curiousaboutcircuits85 · Joined: 08 Apr 2010 Posts: 13

I read the note that says:
// NOTE For faster writing or appending for an application such as a logger,
// uncomment #FAST_FAT below. This will make the FAT library assume
// there is one file on the card to write or append to, thereby
// making writing and appending much faster. Reading is impossible in
// this mode.
// THIS IS NOT TESTED VERY WELL YET!

When it says reading is impossible in this mode, what is it exactly implying? Reading the file in the PC is impossible? If anyone has experience with this, please let me know. I'm making a datalogger that needs constant appending, so I'd like to use this feature to speed up the process. If this prevents the file from being read on a PC, it's useless to me. Thank you

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Consider the context. For a data logger, normally it would log events
such as temperature. Then after some time, the user would pull the
memory card out of the logger and put it into his PC and read it there.
So for a data logger, it doesn't matter if the PIC can't read the memory
card. It will be read by the PC.

curiousaboutcircuits85 · Joined: 08 Apr 2010 Posts: 13

Again, thanks for your reply.

So, from this, I am getting that if I wanted to make one file and write and append to it, the PIC MCU wouldn't be able to read the data. I am trying to log weight data by personal identification number that will be assigned to many people. For example, Joe has a personal identification number 4556 along with which his weight will be recorded. But, the PIC needs to be able to locate the number so that his weight could be changed when Joe's weight changes. In order for me to do this, would I have to make one file per person, or is it possible for me to do it in one file for all individuals being recorded. Thanks again for your help

Ttelmah · Joined: 11 Mar 2010 Posts: 19537

Yes, but not using FAST_FAT.
The 'point' about FAST_FAT, is you gain speed, by dealing with the FAT storage as a single entity (one file), and just writing to it. What you are talking about is a normal FAT file system...

Best Wishes