storing massive amount of data

Guest · Posted: Wed Nov 23, 2005 11:00 am

hi,

my code needs to access big size arrays, say one of them has nearly 700 elements, which are used to plot some graphics on LCD. I am finding trouble storing them coz' I am defining these arrays as constant which means they are stored in flash memory ( I am using 18f) but at the mean time I am running out of rom!

I am considering taking these big arrays out of rom and store them somewhere else. I considered eeprom but speed is demanding for the code which means refleshing the LCD with different bit maps in a high speed. Storing in eeprom would mean loading from eeprom which reduces the speed.

Any good thoughts at all?

Neutone · Joined: 08 Sep 2003 Posts: 839 Location: Houston

How many bytes do you need to store? How large is your code without the Arrays? What chip are you using?

Log into the forum.

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

Check out thread http://www.ccsinfo.com/forum/viewtopic.php?p=51453&highlight=#51453 It starts on a differenr topic, but at the end a few mass-storeage methods are discussed.

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

If you have exhausted the choice of 18F PICs (such as those with 256K program memory) you might want to look at MMC/SD. This gives you access to several GB per card. Because you do not need PC compatibility (do not need FAT file system), reading and writing is straight forward and at high speed.
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http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

ye · Joined: 11 May 2005 Posts: 57 Location: london

Sorry neutone, now I log on.

I am using 18f8722 and so far I've used 60% of rom. I've roughly estimated that without all the constant arrays, there will be a reduction of nearly 20% - 25% of the entire rom space.

asmallri, I did think about MMC and actually I have some modules of code implementing MMC in hand. However the problem is not about the size of external memory, it's about the speed of loading and saving instead.

As I stressed all these templates are used as bit maps on LCD which means the speed is pretty critical.

I don't know in which way I could store these big arrays while keeping a good speed......

Cheers

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

ye · Joined: 11 May 2005 Posts: 57 Location: london

what about storing them in internal rom using #rom or external eeprom, considering the speed again?

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

Retrieval is much faster than storage for all these technologies.

internal rom and internal EEPROM are the fastest and are effectively equal in speed.

Other methods are slower because of the media access mechanisms and bus access speeds. For example, if you are using an external EEPROM with 1 400K I2C bus then your access speed is limited principly by the bus. A 24LCxx at 1M I2C bus will be ten times slower than a 25LCxx with a 10M SPI bus.

For an equal bus speed, an EEPROM will be faster than a SD Card.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

ye · Joined: 11 May 2005 Posts: 57 Location: london

Thank you guys, I think I have got the answers to this problem which has been haunting me for long.

All the best