Datasheet

753
SAM9263 [DATASHEET]
Atmel-6249N-ATARM-SAM9263-Datasheet_14-Mar-16
39.8.2 Data Transfer Operation
The MultiMedia Card allows several read/write operations (single block, multiple blocks, stream, etc.). These kind
of transfers can be selected setting the Transfer Type (TRTYP) field in the MCI Command Register (MCI_CMDR).
These operations can be done using the features of the Peripheral DMA Controller (PDC). If the PDCMODE bit is
set in MCI_MR, then all reads and writes use the PDC facilities.
In all cases, the block length (BLKLEN field) must be defined either in the mode register MCI_MR, or in the Block
Register MCI_BLKR. This field determines the size of the data block.
Enabling PDC Force Byte Transfer (PDCFBYTE bit in the MCI_MR) allows the PDC to manage with internal byte
transfers, so that transfer of blocks with a size different from modulo 4 can be supported. When PDC Force Byte
Transfer is disabled, the PDC type of transfers are in words, otherwise the type of transfers are in bytes.
Consequent to MMC Specification 3.1, two types of multiple block read (or write) transactions are defined (the host
can use either one at any time):
 Open-ended/Infinite Multiple block read (or write):
The number of blocks for the read (or write) multiple block operation is not defined. The card will
continuously transfer (or program) data blocks until a stop transmission command is received.
 Multiple block read (or write) with pre-defined block count (since version 3.1 and higher):
The card will transfer (or program) the requested number of data blocks and terminate the transaction. The
stop command is not required at the end of this type of multiple block read (or write), unless terminated with
an error. In order to start a multiple block read (or write) with pre-defined block count, the host must correctly
program the MCI Block Register (MCI_BLKR). Otherwise the card will start an open-ended multiple block
read. The BCNT field of the Block Register defines the number of blocks to transfer (from 1 to 65535 blocks).
Programming the value 0 in the BCNT field corresponds to an infinite block transfer.
39.8.3 Read Operation
The following flowchart shows how to read a single block with or without use of PDC facilities. In this example (see
Figure 39-10), a polling method is used to wait for the end of read. Similarly, the user can configure the interrupt
enable register (MCI_IER) to trigger an interrupt at the end of read.