DMA controller (DMA) RM0090
316/1731 DocID018909 Rev 11
memory 0 to 1 (or from 1 to 0) depending on the value of CT in the DMA_SxCR register in
accordance with one of the two above conditions.
For all the other modes (except the Double buffer mode), the memory address registers are
write-protected as soon as the stream is enabled.
10.3.10 Programmable data width, packing/unpacking, endianess
The number of data items to be transferred has to be programmed into DMA_SxNDTR
(number of data items to transfer bit, NDT) before enabling the stream (except when the
flow controller is the peripheral, PFCTRL bit in DMA_SxCR is set).
When using the internal FIFO, the data widths of the source and destination data are
programmable through the PSIZE and MSIZE bits in the DMA_SxCR register (can be 8-,
16- or 32-bit).
When PSIZE and MSIZE are not equal:
• The data width of the number of data items to transfer, configured in the DMA_SxNDTR
register is equal to the width of the peripheral bus (configured by the PSIZE bits in the
DMA_SxCR register). For instance, in case of peripheral-to-memory, memory-to-
peripheral or memory-to-memory transfers and if the PSIZE[1:0] bits are configured for
half-word, the number of bytes to be transferred is equal to 2 × NDT.
• The DMA controller only copes with little-endian addressing for both source and
destination. This is described in Table 46: Packing/unpacking & endian behavior (bit
PINC = MINC = 1).
This packing/unpacking procedure may present a risk of data corruption when the operation
is interrupted before the data are completely packed/unpacked. So, to ensure data
coherence, the stream may be configured to generate burst transfers: in this case, each
group of transfers belonging to a burst are indivisible (refer to Section 10.3.11: Single and
burst transfers).
In direct mode (DMDIS = 0 in the DMA_SxFCR register), the packing/unpacking of data is
not possible. In this case, it is not allowed to have different source and destination transfer
data widths: both are equal and defined by the PSIZE bits in the DMA_SxCR MSIZE bits are
don’t care).
Table 45. Source and destination address registers in Double buffer mode (DBM=1)
Bits DIR[1:0] of the
DMA_SxCR register
Direction Source address Destination address
00 Peripheral-to-memory DMA_SxPAR
DMA_SxM0AR /
DMA_SxM1AR
01 Memory-to-peripheral
DMA_SxM0AR /
DMA_SxM1AR
DMA_SxPAR
10 Not allowed
(1)
1. When the Double buffer mode is enabled, the Circular mode is automatically enabled. Since the memory-
to-memory mode is not compatible with the Circular mode, when the Double buffer mode is enabled, it is
not allowed to configure the memory-to-memory mode.
11 Reserved - -
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