On Fri, Mar 27, 2009 at 11:21:59AM -0700, Bob Furber wrote: > Bobby Clark wrote: > >> Did a little bit more checking. The smallest block size appears to be >> 512 bytes. The more common block size is 1024 bytes to 2048 bytes for >> the larger cards. >> > > While they may exist, I have not yet encountered a SD card with a block > length > 512 bytes. A 2GB SD card is accessed 512 bytes at a time even > though the block length is stated as 1024 bytes as a hack to calculate > the total number of bytes. The spec for SDHC cards is a fixed block > length = 512 bytes: > > Simplified physical layer specification > <http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf> > > > (http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf) > > pg 41: > "In High Capacity Cards, the 32-bit argument of memory access commands > uses the memory > address in block address format. Block length is fixed to 512 bytes,.." > > Keep in ming that it is getting increasingly difficult to purchase SC > cards that are smaller than 2GB. Tomorrow it will be difficult to > purchase SD cards that are smaller than 4GB. So we may want to think > about getting used to SDHC cards.
Well I suspect that given the number of no SDHC compatible devices out there, the market for 2GB SD cards won't dissappear for a while, although smaller cards likely will go away. Certainly any new device I buy better be SDHC compatible (if it uses the SD form factor that is). -- Len Sorensen _______________________________________________ uClinux-dev mailing list [email protected] http://mailman.uclinux.org/mailman/listinfo/uclinux-dev This message was resent by [email protected] To unsubscribe see: http://mailman.uclinux.org/mailman/options/uclinux-dev
