Lpc2000

Perhaps someone who is better versed in MMC SPI stuff should take a good 
look at Philips AN10406.  There appears to be some problems with the 
example code it contains.  Two issues jump right out in the file: 
spi_sd.c...

In mmc_init(), look at the _second_ for() loop:
======== begin mmc_init() ==========
int mmc_init( void )
{
   DWORD i;
   /* Write data pattern for testing */
   for(i=0;i<MMC_DATA_SIZE;i++) {
      MMCWRData[i] = i;
   }
   SDStatus = 0;
#if !USE_CS
   IOCLR0 = 0x00100000; /* clear SPI SSEL */
#endif
   /* Initializes the card into SPI mode by sending 80 clocks */
   for(i=0; i<10; i++) {
      MMCCmd[i] = 0xFF;
   }
   SPI_Send( MMCCmd, 10 );
======== snip =================

The sizeof(MMCCmd) is only 8 bytes, not 10.

While that is not too bad, it gets more interesting as you read the 
mmc_block_write().  During mmc_init(), CMD16 has set the blocksize to 
0x200 (512 bytes), okay?  But, when they write the data during 
mmc_block_write(), they only write 8 bytes.  Then they proceed to hold 
the chipselect down and poll 255 times for a completion status code!  Of 
course, it dies, while the MMC gets deadlocked waiting for the rest of 
the data...

Another issue is that the mmc_write_block() does not look at BUSY from 
the MMC, but assumes a delay loop is an answer to when a write has 
completed!!!

With my understanding of MMC and the reading of the code in AN10406, it 
looks as if mmc_block_write() is never going to write a block to the 
MMC?  After compiling and debugging the code for a few hours, I'm 
satisfied that there are problems with it (appnote code).

The night was not a total loss, working with the app note had made me go 
back and take a critical look at the MMC spec + my code.  Heh, my code 
is working flawlessly now!

IMHO, I strongly urge Philips to remove AN10406 from their website until 
a code review has been performed.


Regards,

TomW




-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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