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6.5.4 Memory Scatter-Gather Transfer
In scatter-gather transfer mode, first the DMAC, using the primary data structure, copies a data structure from the
data structure table, which has been prepared with multiple data structures included in advance, to the alternate data
structure, and then it performs DMA transfer using the alternate data structure. The DMAC performs this operation
repeatedly. By programming the transfer mode of the data structure located at the end of the table as a basic transfer,
the DMA transfer can be terminated with a transfer completion interrupt. This mode requires a DMA transfer request
only for starting the first data transfer. Subsequent data transfers are performed by auto-requests.
Figure 6.5.4.1 Example of Data Structure Table for Scatter-Gather Transfer
Transfer using primary data structure
(cycle_ctrl = 0x4, 2
DMA transfer request
Figure 6.5.4.2 Memory Scatter-Gather Transfer Operation Example
S1C31D41 TECHNICAL MANUAL
(Rev. 1.1)
Reserved
Control data
Transfer destination end pointer
Transfer source end pointer
Reserved
Control data
Transfer destination end pointer
Transfer source end pointer
Reserved
Control data
Transfer destination end pointer
Transfer source end pointer
Reserved
Control data
Transfer destination end pointer
Transfer source end pointer
R
= 4, N = 16)
Task A setting
Copy the data structure for
Task A to the alternate data structure.
Task B setting
Copy the data structure for
Task B to the alternate data structure.
Task C setting
Copy the data structure for
Task C to the alternate data structure.
Task D setting
Copy the data structure for
Task D to the alternate data structure.
Seiko Epson Corporation
6 DMA CONTROLLER (DMAC)
Data structure for Task D
Data structure for Task C
Data structure for Task B
Data structure for Task A
Transfer using alternate data structure
(cycle_ctrl = 0x5, 2
Task A
(cycle_ctrl = 0x5, 2
Task B
Auto-request
Auto-request
Auto-request
(cycle_ctrl = 0x5, 2
Task C
(cycle_ctrl = 0x1, 2
Task D
R
= 4, N = 3)
R
= 2, N = 8)
R
= 8, N = 5)
R
= 4, N = 4)
DMA transfer
completion interrupt
6-7
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