Data Storage

kmp84 · Joined: 02 Feb 2010 Posts: 346

Hello,

For now I have to store about 2000 rfid tags numbers 10 bytes long.
On my hardware I have x2 FM24W256 i2c F-RAMs, AT45DB041E SPI memory and SD Card.
Which memory will be the best choice?
I have made some tests with i2c F-RAM and when I get a new card number and have to compare if it exists, it takes about 5 sec. which is acceptable, but if cards are more (10 000)?

P.S I have no driver for AT45DB041 and SD card.

Best Regards!

newguy · Joined: 24 Jun 2004 Posts: 1907

If you swap the I2C FRAM for SPI FRAM, you should be able to cut your search time by a factor of ~10. 400kHz clock vs 5MHz+.

dluu13 · Joined: 28 Sep 2018 Posts: 395 Location: Toronto, ON

If you use SD card and you don't want to buy a driver, mmcsd.c driver provided by CCS works after a number of tweaks. There are a bunch of sticky threads on the topic. I was never able to get fat.c working with it though.

temtronic · Posted: Sat Aug 29, 2020 1:30 pm

How fast is the PIC running ?

What kind of 'compare' algorithm are you using ??

My 'gut' says 5 seconds for a search/compare is way too long. I was accessing 6000 item databases, 10 byte 'stock number' and it was a lot faster than 5 seconds on a Z80 running 2MHz clock.

Hmm, which PIC ? as one with lots of RAM and EEPROM should be faster than external I2C or SPI devices.

kmp84 · Joined: 02 Feb 2010 Posts: 346

kmp84 · Joined: 02 Feb 2010 Posts: 346

kmp84 · Joined: 02 Feb 2010 Posts: 346

newguy · Joined: 24 Jun 2004 Posts: 1907

temtronic · Posted: Sat Aug 29, 2020 2:55 pm

re: ...

Ttelmah · Joined: 11 Mar 2010 Posts: 19506

Lets think for a moment. A memcmp on ten bytes, should only take perhaps
50 instruction times.
Assume the 'search for' value is sitting in an array, and the 'search in'
value is read in on I2C. Reading these at 400KHz, will take 2000*10*
2.5uSec * 2(say) *8 (bit versus byte) *1.5 (address) = 1.2 seconds.
So perhaps 1.2 seconds. Then if the processor is running at (say)
32MHz (8 MIPS), the search would add an average (assuming you average
searching half the records), of perhaps a tenth of a second. So it should be
totally easy to do this in well under 1.5 seconds.
The figure of 5 seconds, suggests something is slowing this a lot. Possibly the
I2C is only being run at 100KHz, or software I2C is being used?.

kmp84 · Joined: 02 Feb 2010 Posts: 346

Hi mr."Ttelmah",

Yes Software i2c are used. Also i have i2c bus speed limits max=400 Khz because on the same bus has RTC (mcp79410).

Ttelmah · Joined: 11 Mar 2010 Posts: 19506

Seriously use hardware I2C.....
Even if it means changing the chip.
Software I2C, even if set for 400KHz, is likely to only be doing something
like 130KHz. Hardware will make a huge difference to the performance.
I'd expect the time to be well under half of what you currently have,
if you can switch to using the hardware.....

kmp84 · Joined: 02 Feb 2010 Posts: 346

Hi,

What will be the appropriate i2c speed when switch to hardware i2c?
(Max speed for MCP79410 = 400kHz). Pull res. = 2k at 3v3?
Is it a good idea to switch to SPI AT45DB041E? (Some working driver?)

Best Regards!

Ttelmah · Joined: 11 Mar 2010 Posts: 19506

Just set the I2C, to 400K. This is the maximum for standard I2C 'FAST' mode.
Yes, using an SPI chip would be a lot faster. Data transfer times perhaps
5* faster in the 'real' world. The I/O part of the driver would need
tweaking.
There are other things that could make a lot of difference though. If the data
is sequential use a 'page mode' driver for your existing chip. This will boost
the overall performance possible 50%, Removes the need to keep sending
the address to be read. These have been published here before.

kmp84 · Joined: 02 Feb 2010 Posts: 346

Thank you All for suggestions!
I'll try to decrease time for searching in "F-RAM DB".

Best Regards!