Hi Lucas, On Mon, Jul 07, 2014 at 10:53:20AM +0200, Lucas Stach wrote: > This has nothing to do with barebox, but I feel this needs an answer as > a lot of misinformation is spread here. > Thanks for your answer. Yes, it's off-topic but I always feel bad when I heard "eMMC". > Am Montag, den 07.07.2014, 09:06 +0200 schrieb Alexander Aring: > [...] > > > > btw.: that's why eMMC is evil. > > > > Raw-Flash: > > > > Disadvantage: > > - you can't replace it. > > > > Advantage: > > - no mcu in the middle, access the raw Flash. > > This isn't an advantage. If your not working for the NAND flash > manufacturer you will have an extremely hard time getting the wear > leveling parameters right. Having this abstracted behind an MCU that > actually know about the flash chip behind it is a good thing. > yes, but I think that a mtd filesystem can do a better scheduling of erase/write/read cycles than the integrated mcu with an abstracted block device. I need to test it myself, to see what the mcu exactly do and this depends on manufacturer. > > > > > > - MMC/SD: > > > > Disadvantage: > > - mcu in the middle, abstract block device. OS doesn't know about this. > > No disadvantage, see above. > > > > > Advantage: > > - you can replace it. > > > > > > Combines these Disadvantage and Advantage you will get: > > > > Disadvantage: > > - mcu in the middle, abstract block device. OS doesn't know about this. > > - you can't replace it. > > > > Advantage: > > - maybe a little bit cheaper... > > - maybe avoid some bad connections (never expired by using sd cards) > > > You are neglecting the fact that the eMMC interface can be driven with a > lot higher clock speeds compared to an SD card. Also most eMMCs have an > interface width of 8 bits, which is double the SDs 4 bit. > okay, I didn't know that. Does barebox use the 8 bit interface at the moment? > This amounts to a lot more raw speed on the interface side and most > eMMCs are actually capable of supplying data at those rates. > > Also eMMC provides some really useful additional features like the boot > partitions and health checks. > > While SD cards may be convenient for the casual hobbyist user when it > comes to real embedded devices, where speed and reliability matters, > eMMC has a huge lead. > > Raw NAND is only an option if your device manufacturing runs are big > enough that the lower price for NAND stacks up enough to make up the > additional development time (cost) you need to get things right. Note > there is a big difference here between getting it working and getting it > right. > So now I have the question about "Why they don't make a new sd/mmc card holder standard and sells replaceable cards". I could say that to every electronic device, but maybe it's better that there is no new standard. :-) - Alex _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
