MMC read_block problem

f00dstamps · Joined: 28 Mar 2006 Posts: 10 Location: Kansas City, MO

i am having a problem reading a block from MMC. i can successfully RESET, INITialize, and SET_BLOCKLEN.

when i send the command to READ_BLOCK, i never get the FEh start byte. i either get 00h or FFh's.

any ideas?

f00dstamps · Joined: 28 Mar 2006 Posts: 10 Location: Kansas City, MO

bump for help guys.

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

Search the internet for the terms "spi timing" and MMC, this will give you several links to a 3-page document with timing diagrams for the MMC cards in SPI bus mode, for example http://kilm.by.ru/im/flash/mmc/pdf/spitiming.pdf

The sequence for executing the read from MMC is as follows:
- Send the Read command (51h)
- Read 1 to max. 8 bytes of 0xFF until you get a 0x00, this is the command acknowledge.
- Read 1 to many (depending on card) bytes of 0xFF until you get the 0xFE start byte.
- Read all data bytes (length set by CMD16).
- Read the two crc-bytes.

f00dstamps · Joined: 28 Mar 2006 Posts: 10 Location: Kansas City, MO

ckielstra - thanks for your response. i already have the spitiming diagram and i already follow the sequence you outline.

i send the read command until i get 00h returned. after that i send the read command until i get FEh returned. i read up to 8192 times but i have yet to get the FEh.

perhaps i have a problem with my open_file function.

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

Can you post your read function here? If you can't for confidential reasons, then mail it to me using the mail function of this forum.