If SF’ isn’t equal to SF, SF’ is used as SF. Sectors per FAT(SF’) is recalculated as following: Maximum Cluster Number(MAX) is computed as following: If NOM isn’t equal to BU, NOM is added BU. Number of Sectors in Master Boot Record(NOM) is computed as following: Number of sectors in the system area(SSA) is computed as following: Sectors per FAT(SF) is computed as following:
FAT bits(12, 16) is determined by SC and TS.ħ. Total Sectors(TS) is the number of all sectors of the area.Ħ. Number of Root-directory Entries(RDE) is 512.ĥ. Sectors per Cluster(SC) is determined from the area size.Ģ. Here is an example of one algorithm for FAT12/FAT16 parameters from the standard with proprietary formulas and tables missing.ĭata Area should be formatted by the following steps.ġ. You can't just decide on a partition size and location. The document even specifies the MBR and uses it to control reserved space. It implements the SD associations standard which is specified in a 70 page Confidential document. If you wish you can use my SdFormatter example in SdFat. Linux has tables for handling quirks of USB flash keys and USB hard drives. What I don't understand is why Linux does not have a decent formatter for SD cards. Sadly this is the organization that all the big SD manufactures control and your SD card will be manufactured to their standards.Īs I said before, the SD association specifies a specialized version of FAT16/FAT32 and now exFAT for SDXC cards that is optimal for the flash layout and chips used in SD cards. Ok, ok, now what if you don't happen to be running Windoze or Max OS? And why should you trust that obscure company/organization, when they themselves declare: This command will not work for standard SD cards (2 GB or less). The card is not MBR and file structures are miss-aligned. The mkfs.vfat command suggested by pylon is the worst case.
#SD CARD FORMATTER FAT32 MAC OS X#
I don't have a machine with a new version of OS X so I can't be sure if Mac OS X still formats SD cards incorrectly. I have had OS X format an SD card GPT instead of MBR which is unusable on Arduino. Mac OS X adds lot of non-standard hidden files and directories. The SD standard is for an MBR volume so this is not strictly correct.
#SD CARD FORMATTER FAT32 WINDOWS#
Windows 7/8 formats an erased SD as a super floppy but if you choose the correct cluster size, file structures are aligned well. Windows just cleans the card and preserves the correct SD format. Windows 7/8 does a good job of reformatting a healthy SD card. Here are results of using mkfs.vfat, the SD Association Formatter, and the SdFat formatter Formatted with suggested mkfs.vfat commandįreeSpace: 31907.12 MB (MB = 1,000,000 bytes)ĭata area is not aligned on flash erase boundaries!ĭownload and use formatter from Formatted with SD Associations formatterįreeSpace: 31902.30 MB (MB = 1,000,000 bytes)įreeSpace: 31902.37 MB (MB = 1,000,000 bytes) I was able to access the standard as a consultant and implemented the SdFat formatter example according to this specification. Unfortunately the SD association's standard for formatting SD cards is only available to members. This is done by placing reserved blocks in the correct places in the file system. You can only depend on the SD association's formatter to place file structures correctly to line up with flash chip boundaries. Linux does not correctly format SD cards. It will always produce the optimum format for your card. These are extreme cases but I do often see this type problem so please use this formatter. Maximum latency: 1920 usec, Minimum Latency: 80 usec, Avg Latency: 437 usec Maximum latency: 117636 usec, Minimum Latency: 84 usec, Avg Latency: 1113 usec Maximum latency: 1912 usec, Minimum Latency: 84 usec, Avg Latency: 265 usec Maximum latency: 58888 usec, Minimum Latency: 84 usec, Avg Latency: 273 usec Write takes about four times longer with FAT32 and small clusters. Here are results running the SdFat bench sketch on this card. Same card formatted FAT32 with small clusters on Windows.įreeSpace: 2065.05 MB (MB = 1,000,000 bytes) See for more details on code.įreeSpace: 2093.32 MB (MB = 1,000,000 bytes)
#SD CARD FORMATTER FAT32 FREE#
Time to determine free space with a properly formatted card using the SdInfo sketch. This type performance hit will also be true for seek.
First is an extreme case for determining free space on an SD. Here are some examples that show what can happen. Always format SD cards using SD Formatter.
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