SDMA Channels and IDMA Emulation
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
19-11
Figure 19-8
shows the descriptor structure.
Table 19-7
describes an IDMA descriptor’s status-and-control field.
Offset
0
1
2
3
4
5
6
7
15
0x00
V
—
W
I
L
—
CM
—
0x02
DFCR
SFCR
0x04
Buffer Length
0x06
0x08
Source Buffer Pointer
0x0A
0x0C
Destination Buffer Pointer
0x0E
Figure 19-8. IDMA Buffer Descriptor Structure
Table 19-7. 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
—
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).
3
I
Interrupt. Enable the maskable auxiliary-done (AD) interrupt
0 IDSR[AD] is not flagged after this BD is processed.
1 IDSR[AD] is flagged after this BD is processed.
4
L
Last. Marks the end of a buffer chain and enables the maskable DONE interrupt
0 Not the last BD of a buffer chain
1 Last BD of a buffer chain. When the transfer count is exhausted, IDSR[DONE] is flagged,
regardless of the I bit
5
—
Reserved
6
CM
Continuous mode. Selects buffer-chaining or auto-buffering; see
Section 19.3.4.2, “Auto-Buffering
and Buffer-Chaining
.”
0 Normal mode (buffer-chaining). The CP clears the V bit after this descriptor is processed.
1 Continuous mode (auto-buffering). The CP does not clear the V bit after this descriptor is
processed.
7–15
—
Reserved
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