SD Card performance: generates freezes in TomTom

[edsub]

As mentioned in another thread, my TomTom started freezing after about one week of fine operation.

After investigating al kinds of things related to my new BT GPS, I (with the suggestion of some german forum on PocketPC / MDA) found out that the cause is in the combination of extra POI files (well, just 1!) and storage of the maps on my Kingston 256MB SD card (which in fact is a SD-M256B1 Toshiba manufactured card).
Apparantly the read-speed of the card (or its interface) is too low to get all the data to TomTom in time. The problem gets worse when driving with higher speeds (ie. on the motorway).

:idea:
If you experience the same behaviour try this:

Don't start TomTom, just start TomTomGPS. If it doesnt freeze over a certain amount of distance at motorway speed, then the SD card speed might very well be the problem.

To get extra proof, try to minimize the data that has to be read from the SD card:
1. Disable POI, or
2. Put your map in main-memory

Do the test again, now WITH TomTom: If the cause of the freezes is the SD card speed, it should not happen again.

Final questions that need to be answered:
1. Is the limitation in speed within the MDAII or witin the SD card? Rudegar mentioned somewhere the limitation is within the MDAII, On a German forum it is claimed the MDA has an extremely fast interface thus generating issues with slow SD cards (mostly noticeable with writing the card).
2. Which cards have a high enough read-speed?
3. How to improve the read-performance of any SD-card?

[JRC]

I have the same problem. The SD port has very bad performances ...

[kitarolivier]

Did you tried with a non BlueTooth GPS ?
My father has an iPaq 2210, and if maps are located on SD Card, after +/- 5 mins of driving, the BT GPS freezes and does not update position (BT connection lost). The bug comes from an intense memory access to SD card (reading maps + sound files) during bluetooth access (known bug). To solve the problem, I had to put maps on the CompactFlash card instead of the SD, and now itf works file.

Hope this can help someone.

Regards, and drive carefully :)

Olivier.

[edsub]

My best solution for now is:
Store as much in main memory (at least programs & soundfiles)
Unfragment SD storage (still looking for a freeware tool . . )
optional: Disable POI extra files

and maybe: Faster SD card (but that only helps if the interface is fast enough.

[edsub]

Read speed of my Kingston (Toshiba) 256MB SD card (benchmarked by Pocket Mechanic trial) is avg. 0,89MB/s
Meaning that I am only halfway the 'typical' tranfer rate as advertised of 2MB/sec!!!

Does anyone come near the 'typical' 2MB/s value??


Did not measure write-speed, as that is not critical for TomTom use.

[kitarolivier]

Unfragment SD storage (still looking for a freeware tool . . )


I don't understand the need of UNFRAGMENTING SD Cards, since there is no 'SEEK' time on this kind of storade (in opposite to disks, tapes, etc... where there is a mechanical time to reach the data).

[edsub]

Typical speed-increase might not be as big as with mechanical drives, but still the access-software has to put together the bytes in correct order to the requesting application. That takes time, namely the random acces-time wich is much (relatively speaking) bigger than sequential seek.