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| SD Card performance http://www.at91.com/samphpbb/viewtopic.php?f=13&t=780 |
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| Author: | Onitake [ Mon Jun 06, 2005 12:45 pm ] |
| Post subject: | SD Card performance |
i'm having performance issues with the SD Card driver: since write-back caching is disabled, all data gets written immediately. and, in contrary to read access, only in chunks of 1/2 sector or 1 sector (why?). i found out that soft-caching (writing into a buffer of 1MB and calling WriteFile() for this buffer) helps a bit and gives me a maximum data rate of about 1.2MB/s on write and 1.7MB/s on read when doing nothing else. strange thing is, the SD Cards we're using can handle up to 9MB/s on both read and write (or a little less on write). what's causing this discrepancy? is the hardware too slow? or is it just beacuse we're not using write-back caching? there's another small thing: in debug mode, every written chunk produces 4 lines of debug message noise. it would be much better to turn that off or at least reduce it to one line. |
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