DMA Programming Model
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
14-49
—
20–19
Reserved. Write to zero for future compatibility.
BTSZ
18–16
Basic Transfer Size
The basic transfer size issued by the request. If BTSZ is greater
than TSZ, the DMA controller uses the TSZ value.
000
64 bytes.
001
1 byte.
010
2 bytes.
011
4 bytes.
100
8 bytes.
101
16 bytes.
110
32 bytes.
111
64 bytes.
—
15–11
Reserved. Write to zero for future compatibility.
LAST
10
Last Buffer In Chain
Set this bit only to avoid an endless task condition when CONT is
set and CONTD is smaller than BD.
0 Not the last buffer in the chain.
1 Last buffer in the chain.
BD
9–8
Buffer Dimension
Indicates the dimension of the buffer.
00 1 dimension.
01 2 dimensions.
10 3 dimensions.
11 4 dimensions.
SSTD
7–6
Set Status Dimension
When BD_MD_SIZE reaches zero and BD_MD_ATTR[SST] = 1,
the status bit is set for the channel in DMASTR. For details, see
page 14-36. The SSTD field defines the dimension on which the
status bit is set.
00 BD_MD_SIZE reached zero, 1D.
01 M2D_COUNT reached zero, 2D.
10 M3D_COUNT reached zero, 3D.
11 M4D_COUNT reached zero, 4D.
FRZD
5–4
Freeze Dimension
When the selected dimension is processed, the internal logic
masks all channel requests and freezes the channel. The host
must defrost the channel for further service.This field is valid only
if FRZ is set in the BD_MD_ATTR.
00 Mask and freeze channel when first
dimension ends.
01 Mask and freeze channel when second
dimension ends.
10 Mask and freeze channel when third
dimension ends.
11 Mask and freeze channel when fourth
dimension ends.
CONTD
3–2
Continuous Buffer Mode Dimension Select
Indicates the dimension after which the channel switches to the
next multi-dimensional BD. This field is valid only if CONT is set in
the BD_MD_ATTR.
Notes: 1.
The value must not be greater than BD.
2.
When NBD is equal to the current BD and CONT is
set, CONTD must equal BD.
3.
If CONT is set and CONTD < BD, the BD area is
updated by the DMA controller. Do not access this
area until the DMA task is completed.
4.
If CONT is set, CONTD < BD, and NPRT is different
from the current port, MR must be set an MRD must
be equal to CONTD.
00 Switch to next BD when BD_MD_SIZE
reaches zero, 1D
01 Switch to next BD when M2D_COUNT
reaches zero, 2D.
10 Switch to next BD when M3D_COUNT
reaches zero, 3D.
11 Switch to next BD when M4D_COUNT
reaches zero, 4D.
Table 14-31. BD_MD_ATTR Field Descriptions (Continued)
Bits
Description
Settings
Содержание MSC8144E
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