[uClinux-dev] 5282 and 2GB SD cards

[Steve Bennett]

Hi Wolfgang,

Works like a charm --  use READ_BL_LEN for calculating the card size,
but just use 512 bytes blocks for I/O .

Thanks,
Steve

On 21/02/2007, at 7:27 AM, Wolfgang Mües wrote:

> Hi Bob,
>
> On Montag, 19. Februar 2007, Bob Furber wrote:
>> Hi Wolfgang,
>>
>>> please note that ALL SD cards have 512 bytes blocksize. All I/O is
>>> in 512 Byte blocks.
>>>
>>> The blocksize of 1KByte which is reported for 2GB cards is ONLY to
>>> compute the capacity of the card.
>>
>> Good stuff!
>>
>> Does this mean that if the csd.c_size read from the card should be
>> doubled on 2GB cards? Then the 2GB card can be treated by the
>> software exactly as if it were a 1GB card, but, with twice as many
>> blocks?
>
> Use the official formula for calculating the size in bytes for the SD
> card:
>
>> C_SIZE (Device Size)—This parameter is used to compute the card
>> capacity (does not include security protected area). The memory
>> capacity of the card is computed from the entries C_SIZE, C_SIZE_MULT
>> and READ_BL_LEN as follows:
>>          memory capacity = BLOCKNR * BLOCK_LEN
>>
>>          Where:
>>          BLOCKNR    = (C_SIZE+1) * MULT
>>          MULT           = 2^C_SIZE_MULT+2      (C_SIZE_MULT < 8)
>>          BLOCK_LEN = 2^READ_BL_LEN        (READ_BL_LEN < 12)
>> Therefore, the maximum capacity which can be coded is 4096*512*2048 =
>> 4 GBytes. Example: A four MByte card with BLOCK_LEN = 512 can be
>> coded with C_SIZE_MULT = 0 and C_SIZE = 2047.
>
> As you can see, if you want to code 2 GByte you MUST use a  
> BLOCK_LEN of
> 1024. 4 GByte must use BLOCK_LEN of 2048.
>
> But for doing the actual I/O, all SD cards are using 512 byte sectors.
> Don't use BLOCK_LEN or READ_BL_LEN for this!
>
>> The little information that I have found indicates that the SDHC
>> (High Capacity) has not yet caught on
>
> There _is_ a first data sheet for SDHC cards available from transcend.
> _AND_ I assume that for SDHC cards, the argument of read/write  
> commands
> is not the position in units of bytes, but in units of 512 bytes.  
> So it
> should be possible to extend linux SD drivers to SDHC right now.
>
> regards
>
> Wolfgang
> -- 
> Das Leben kann nur rückwärts verstanden,
> muß aber vorwärts gelebt werden.
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