20-10
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
¥
The byte at ( 3) is the source function code register (SFCR). See
Section 20.3.4.1, ÒFunction Code RegistersÑSFCR and DFCR.Ó
¥
The word at ( 4) is the buffer length, containing the number of bytes for
transfer. It must be greater than zero.
¥
The word at ( 8) points to the beginning of the source buffer in internal or
external memory.
Ñ When the source is a peripheral, this Þeld is ignored in single-address mode. In
dual-address mode, this Þeld contains the peripheral address.
¥
The word at ( 0xC) points to the beginning of the destination buffer in
internal or external memory.
Ñ When the destination is a peripheral, this Þeld is ignored in single-address mode.
In dual-address mode, this Þeld contains the peripheral address.
Figure 20-8 shows the descriptor structure.
Table 20-7 describes an IDMA descriptorÕs status-and-control Þeld.
Offset
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0x00
V
Ñ
W
I
L
Ñ
CM
Ñ
Ñ
Ñ
Ñ
Ñ
Ñ
Ñ
Ñ
Ñ
0x02
DFCR
SFCR
0x04
Buffer Length
0x06
0x08
Source Buffer Pointer
0x0A
0x0C
Destination Buffer Pointer
0x0E
Figure 20-8. IDMA Buffer Descriptor Structure
Table 20-7. IDMA BD Status and Control Bits
Bits
Name
Description
0
V
Valid. Ready for processing.
0 Invalid. Not ready for transfer. The user can write to this descriptor and its buffer. When
buffer-chaining, the CP clears the V bit after the buffer has been transferred.
1 Valid for transfer. The user should not write to this descriptor or its buffer once the V bit is set.
Note: When an error condition is detected, the CP clears the V bit.
1
Ñ
Reserved
2
W
Wrap. Marks the end of the BD table.
0 Not the last descriptor in the BD table.
1 Last descriptor in the BD table. After this descriptor has been processed, the CP wraps the
current BD pointer (IBPTR) back to the top of the BD table (IBASE).
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