Fast calculation of free size

mpe · Joined: 31 Jul 2007 Posts: 13

The DISKFREE() function can be very slow. I have found about 30 s for an nearly empty 2 GB SD-RAM and the CPU running at 7.3 MHz! Sad

Can anybody suggest a faster way to find the size of the free RAM.

taroosheh · Joined: 16 Mar 2007 Posts: 32 Location: Iran

in my project this problem is very bad because this command get 3 seconds or more than

I had to define a long variable and at startup this function called and any times when generate a file or delete add/minus with this variable but this method not very good

I am working on memory allocation table in FAT independence form AVR-DOS maybe this problem solved with any way

good luck

http://www.electrorc.blogfa.com

oe9vfj · Joined: 17 Jun 2004 Posts: 269 Location: Austria, Hard

DISKFREE counts in all FAT-Sectors the free Cluster entries and calculates the Free Disk-space.
The main factor for the time, which DISKFREE needs to do its job is the count of FAT-sectors to check.
I use a 2GB SD-Card from SanDisk (Speed Class 2) and DISKFREE needs less than 1 second to calculate the free Disk space.
This Card is formatted with FAT16 and have 236 FAT-Sectors.
A Card with 2GB formatted in FAT32 have appr. 3800 FAT Sectors. So DISKFREE uses on a FAT32 appr. 16 times the time to get the free disk space.
Cards up to 2GB can be formatted with FAT16.
FAT16 has one disadvantage if you save a lot of very small files. On a 2GB Card the smallest allocation Unit is 32KB, so every File will need at least 32 KB on a 2GB Card formatted with FAT16.
If the majority of your files have 32KB or more, FAT16 will be the better option to format a 2GB Card.

mpe · Joined: 31 Jul 2007 Posts: 13

I am more or less forced to use FAT32 as most of my files are about 10k and the maximum size is 24k.
But my problem was wrongly formulated. I am not really interested in the total free space, but I only want to know, if there is free space for the next file. Therefore. I am modifying the routine to check for 100k free space. This is fast and gives the information I need. The needed time is also independant of the total free size, so I can optimize the code.

anatom · Joined: 06 Dec 2005 Posts: 93

Tiny · Joined: 10 Nov 2010 Posts: 101 Location: The Netherlands

Please will you share with you have modified, I also only need to know if there is freespace for the next logfile.