Alternate Structure
Primary Structure
Primary Structure
Alternate Structure
transfer
continuesusingalternate
BUFFER B
BUFFER A
·
Process data in BUFFERA
·
Reload primary structure
transfers using BUFFERA
BUFFER A
transfers using BUFFERA
transfers using BUFFERB
transfer
continues using alternate
transfer
continues using primary
BUFFER B
transfers using BUFFERB
Pe
rip
hera
l/
DMA
Interru
pt
µ
·
Process data in BUFFERB
·
Reload alternate structure
·
Process data in BUFFERA
·
Reload alternate structure
µ
DMA Controller
Cortex-M3 Processor
T
ime
Peripheral/
DMA
Interrupt
µ
Peripheral/
DMA
Interrupt
µ
SOURCE
DEST
CONTROL
Unused
SOURCE
DEST
CONTROL
Unused
SOURCE
DEST
CONTROL
Unused
SOURCE
DEST
CONTROL
Unused
Functional Description
1156
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
M3 Micro Direct Memory Access ( µDMA)
Figure 16-2. Example of Ping-Pong µDMA Transaction
16.3.6.5 Memory Scatter-Gather
Memory Scatter-Gather mode is a complex mode used when data must be transferred to or from varied
locations in memory instead of a set of contiguous locations in a memory buffer. For example, a gather
µDMA operation could be used to selectively read the payload of several stored packets of a
communication protocol and store them together in sequence in a memory buffer.
In Memory Scatter-Gather mode, the primary control structure is used to program the alternate control
structure from a table in memory. The table is set up by the processor software and contains a list of
control structures, each containing the source and destination end pointers, and the control word for a
specific transfer. The mode of each control word must be set to Scatter-Gather mode. Each entry in the
table is copied in turn to the alternate structure where it is then executed. The µDMA controller alternates