Datasheet

773
SAM9G45 [DATASHEET]
Atmel-6438O-ATARM-SAM9G45-Datasheet_08-Dec-15
35.8.2 Data Transfer Operation
The High Speed MultiMedia Card allows several read/write operations (single block, multiple blocks, stream, etc.).
These kinds of transfer can be selected setting the Transfer Type (TRTYP) field in the HSMCI Command Register
(HSMCI_CMDR).
These operations can be done using the features of the DMA Controller.
In all cases, the block length (BLKLEN field) must be defined either in the HSMCI_MR, or in the HSMCI Block
Register (HSMCI_BLKR). This field determines the size of the data block.
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 HSMCI_BLKR, otherwise, the card will start an open-ended multiple block read. The BCNT field
of the HSMCI_BLKR 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.
35.8.3 Read Operation
The following flowchart (Figure 35-8) shows how to read a single block with or without use of DMAC facilities. In
this example, a polling method is used to wait for the end of read. Similarly, the user can configure the HSMCI_IER
to trigger an interrupt at the end of read.