Public Version
MMC/SD/SDIO Functional Description
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The number of 32-bit accesses to the MMCi.
register that are needed to read (or write) a
data block with a size of MMCi.
[10:0] BLEN, and equals the rounded up result of BLEN
divided by 4.
The maximum block size supported by the host controller is 1024 bytes. This value is hard-coded in the
register MMCi.
[17:16] MBL field and cannot be changed.
A read access to the MMCi.
register is allowed only when the buffer read enable status is
set to 1 (MMCi.
[11] BRE); otherwise, a bad access (MMCi.
[29] BADA) is
signaled.
A write access to the MMCi.
register is allowed only when the buffer write enable status is
set to 1 (MMCi.
[10] BWE); otherwise, a bad access (MMCi.
[29] BADA)
is signaled and the data is not written.
The data buffer has two modes of operation to store and read of the first and second portions of the data
buffer:
•
When the size of the data block to transfer is less than or equal to 512 bytes, meaning the value
written in BLEN is less than or equal to 0x200, two data transfers can occur from one data bus to the
other data bus and vice versa at the same time. The MMC/SD/SDIOi host controller uses the two
portions of the data buffer in a ping pong manner so that storing and reading of the first and second
portions of the data buffer are automatically interchanged from time to time so that data may be read
from one portion (for instance, through a DMA read access on the interconnect bus) while data (for
instance, from the card) is being stored into the other portion and vice versa. When BLEN is less than,
or equal to 0x200 (that is, less than, or equal to 512 bytes), each of the two portions of the buffer that
can be used have a size of BLEN (that is, 32 bits x BLEN div by 4). Do not use a size greater than 2
times this value.
CAUTION
The MMCi.
[4] DDIR bit must be configured before a transfer to
indicate the direction of the transfer.
and
show the buffer management for a write and for a read, respectively.
3386
MMC/SD/SDIO Card Interface
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated