Small Fat/SD library

[Lykos1986]

Hello to everyone!

I was playing with a PIC24F32KA304 micro and the ex_mmcsd.c example.

After the changes at the microcontroller definition and the fuses I try to compile the program but it replies back (MpLab with CCS plug in) that there is not enough memory!!! Is this example so memory hungry that can't fit inside a 16bit 32KB micro?

I've try to decrease a little bit the memory blogs and arrays and I manage to compile and create the hex file (by decreasing the examples functionality as well).

Have you got any other fat/sd driver that is more memory efficient but it is doing almost the same job? I just want to access the SD card and to write/delete data from a txt file.

[Ttelmah]

I just took the example 'as is', changed the processor to yours, made a couple of fuse changes to give a reasonable clock, and compiled it. 12% ROM used, and 36% RAM used. No problems.
What compiler version?. I used 4.141.
It'll fit comfortably in chips with a lot less ROM/RAM than yours.
Then made it into a MPLAB project, and again it worked.

Best Wishes

[Lykos1986]

Sorry, sorry...

I was playing with two SD Card/FAT examples the same day and that's why the mistake! The ex_mmcsd.c is running fine! No problem with the size of the memory at all!

The ex_fat.c is not working because MpLab is saying:
*** Error 74 "SD_Fat.c" Line 486(0,1): Not enough RAM for all variables

CCS Version: 4.140

[jeremiah]

This is a very specialized chip (good for low power and for waking up from sleep with timer1 without an external oscillator among other things). However, one tradeoff for this particular chip is that it has 2k RAM, which means you will need to take special care of how many variables you create and how/where you create them.

I actually use this chip in a lot of applications. The fact that it is 16 bit and 32k ROM space has no impact on the amount of RAM it has.

My guess is that the fat library uses some large buffers that take up all or most of your RAM. If that is the case, then you need to either modify it to work differently or perhaps target a chip better suited for your application.

[Ttelmah]

The code as written, needs just over 1800bytes. Remember as soon as you 'touch' a FAT file system, you need 512bytes for even one sector file, Add the fact that to work the strings have to be 'passed in RAM', and a couple of KB, is needed. The particular problem here is that on the PIC24, RAM is used for the stack. The code will fit on PIC18's with only 2K, but on the PIC24, more RAM is needed for the stack, taking the size required 'up' over the 2K boundary....
It fits merrily on many other 24K chips, but not this one.
The third party library from Brush Electronics, does have an option to minimise the RAM used, basically halving this (but at a speed penalty), and this would fit on the chip, but is not a 'free' library.

Best Wishes

[Lykos1986]

Thank you both for your answers! I will try to find another driver with smaller ROM/RAM footprint. I only need to access a txt file and to write/read text inside it. Nothing else fancy about other FAT functions.

By the way jeremiah, do you know any other PIC24 with the same footprint but better ROM/RAM specs that can replace the one I am using? I will do a research at the Microchips website soon but I am asking in case you know anything about it...

[jeremiah]

In terms of pin count, I've personally used the PIC24FJ64GA004, which has 8k RAM. I've not messed with the FAT or mmcsd libraries however. Also note that a lot changes between the chips (no EEPROM, not as low power, no internal timer1 osc that runs in sleep, some peripheral changes, etc.), so you would need to look at what exactly you need from the chip.

I don't think you will find an exact drop in replacement. Even among chips with the same count, some pins are used differently. Some might be "close" though. It would probably require some soldering magic to get it to fully replace.

[Lykos1986]

Thank you jeremiah and of cource both of you for your help!

I was checking the 24FJ64GA004 datasheet and it needs lot of soldering/hacking in order to fit project but I will find a solution...

[asmallri]

[Ttelmah]

Let me just add here, a 'satisfied customer' using this.

I had a working program, using the CCS code, but needed to add SD/HC support. Realised that the time needed to do this, was vastly larger than the cost of this library, so bought it.

Felt that the examples could be rather improved, but the core library worked very well, - ran first time, and I've got a PIC now running SD SD/HC, FAT16, or FAT32, all without having to worry, and three buffered serials, USB, another I2C bus, yet using less than 2.6KB of RAM....

Best Wishes

[jeremiah]