Figure 39. Fifo Structure - ST STM32F405 Reference Manual

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RM0090
10.3.12
FIFO
FIFO structure
The FIFO is used to temporarily store data coming from the source before transmitting them
to the destination.
Each stream has an independent 4-word FIFO and the threshold level is software-
configurable between 1/4, 1/2, 3/4 or full.
To enable the use of the FIFO threshold level, the direct mode must be disabled by setting
the DMDIS bit in the DMA_SxFCR register.
The structure of the FIFO differs depending on the source and destination data widths, and
is described in
B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Source: half-word
H7 H6 H5 H4 H3 H2 H1 H0
Source: half-word
H7 H6 H5 H4 H3 H2 H1 H0
Figure 39: FIFO
structure.

Figure 39. FIFO structure

Empty
byte lane 3
Source: byte
byte lane 2
byte lane 1
byte lane 0
W3
Empty
byte lane 3
Source: byte
byte lane 2
H7
byte lane 1
byte lane 0
H6
Empty
byte lane 3
byte lane 2
byte lane 1
byte lane 0
W3
Empty
byte lane 3
byte lane 2
H7
byte lane 1
byte lane 0
H6
RM0090 Rev 18
4 words
1/4
1/2
3/4
B15
B 11
B7
B14
B10
B6
B13
B9
B5
B12
B8
B4
W2
W1
4 words
1/4
1/2
3/4
B15
B 11
B7
B14
B10
B6
H5
H3
B13
B9
B5
B12
B8
B4
H4
H2
4 words
1/4
1/2
3/4
H7
H5
H3
H6
H4
H2
W2
W1
4-words
1/4
1/2
3/4
B15
B 11
B7
B14
B10
B6
H5
H3
B13
B9
B5
B12
B8
B4
H4
H2
DMA controller (DMA)
Full
B3
Destination: word
B2
W3, W2, W1, W0
B1
B0
W0
Full
B3
Destination: half-word
B2
H1
H7, H6, H5, H4, H3, H2, H1, H0
B1
B0
H0
Full
Destination: word
H1
W3, W2, W1, W0
H0
W0
Full
B3
Destination: byte
B2
H1
B15 B14 B13 B12 B11 B10 B9 B8
B1
B7 B6 B5 B4 B3 B2 B1 B0
B0
H0
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