Block Read - ST STM32L4x6 Reference Manual

SD/SDIO/MMC card host interface (SDMMC)
select a different card), which will place the card in the Disconnect state and release the
SDMMC_D line(s) without interrupting the write operation. When reselecting the card, it will
reactivate busy indication by pulling SDMMC_D to low if programming is still in progress and
the write buffer is unavailable.
41.4.6

Block read

In Block read mode the basic unit of data transfer is a block whose maximum size is defined
in the CSD (READ_BL_LEN). If READ_BL_PARTIAL is set, smaller blocks whose start and
end addresses are entirely contained within one physical block (as defined by
READ_BL_LEN) may also be transmitted. A CRC is appended to the end of each block,
ensuring data transfer integrity. CMD17 (READ_SINGLE_BLOCK) initiates a block read and
after completing the transfer, the card returns to the Transfer state.
CMD18 (READ_MULTIPLE_BLOCK) starts a transfer of several consecutive blocks.
The host can abort reading at any time, within a multiple block operation, regardless of its
type. Transaction abort is done by sending the stop transmission command.
If the card detects an error (for example, out of range, address misalignment or internal
error) during a multiple block read operation (both types) it stops the data transmission and
remains in the data state. The host must than abort the operation by sending the stop
transmission command. The read error is reported in the response to the stop transmission
command.
If the host sends a stop transmission command after the card transmits the last block of a
multiple block operation with a predefined number of blocks, it is responded to as an illegal
command, since the card is no longer in the data state. If the host uses partial blocks whose
accumulated length is not block-aligned and block misalignment is not allowed, the card
detects a block misalignment error condition at the beginning of the first misaligned block
(ADDRESS_ERROR error bit is set in the status register).
41.4.7 Stream access, stream write and stream read
(MultiMediaCard only)
In stream mode, data is transferred in bytes and no CRC is appended at the end of each
block.
Stream write (MultiMediaCard only)
WRITE_DAT_UNTIL_STOP (CMD20) starts the data transfer from the SDMMC card host to
the card, beginning at the specified address and continuing until the SDMMC card host
issues a stop command. When partial blocks are allowed (CSD parameter
WRITE_BL_PARTIAL is set), the data stream can start and stop at any address within the
card address space, otherwise it can only start and stop at block boundaries. Because the
amount of data to be transferred is not determined in advance, a CRC cannot be used.
When the end of the memory range is reached while sending data and no stop command is
sent by the SDMMC card host, any additional transferred data are discarded.
1412/1693 DocID024597 Rev 3
RM0351