11.4 Pipeline Timing and Throughput
The DMA consists of a 4-stage pipeline as shown in
. The one exception to this is when a DMA
channel is configured to have the McBSP as its data source. A read of a McBSP DRR register stalls the DMA
bus for one cycle during the read portion of the transfer, as shown in
Out
SRC
addr
(N)
Read
SRC
data
(N)
Out
DST
addr
(N)
Out
SRC
addr
(N+1)
Write
DST
data
(N)
Gen
SRC
addr
(N+1)
Gen
DST
addr
(N+1)
Gen
SRC
addr
(N+2)
Read
SRC
data
(N+1)
Out
DST
addr
(N+1)
Out
SRC
addr
(N+2)
Write
DST
data
(N+1)
Gen
DST
addr
(N+2)
Gen
SRC
addr
(N+3)
Read
SRC
data
(N+2)
SYSCLK
Addr bus
Data bus
Generate
address
Figure 11-3. 4-Stage Pipeline DMA Transfer
Out
SRC
addr
(N)
Read
SRC
data
(N)
Out
DST
addr
(N)
Write
DST
data
(N)
Gen
SRC
addr
(N+1)
Gen
DST
addr
(N+1)
Gen
SRC
addr
(N+2)
Out
DST
addr
(N+1)
Write
DST
data
(N+1)
Gen
DST
addr
(N+2)
SYSCLK
Addr bus
Data bus
Generate
address
Out
SRC
addr
(N+1)
Read
SRC
data
(N+1)
Figure 11-4. 4-Stage Pipeline With One Read Stall (McBSP as source)
In addition to the pipeline there are a few other behaviors of the DMA that affect it’s total throughput
• A 1-cycle delay is added at the beginning of each burst
• A 1-cycle delay is added when returning from a CH1 high priority interrupt
• 32-bit transfers run at double the speed of a 16-bit transfer (that is, it takes the same amount of time to
transfer a 32-bit word as it does a 16-bit word)
• Collisions with the CPU may add delay slots (see
For example, to transfer 128 16-bit words from ADC to RAM a channel can be configured to transfer 8 bursts of
16 words/burst. This will give:
8 bursts * [(4 cycles/word * 16 words/burst) + 1] = 520 cycles
If instead the channel were configured to transfer the same amount of data 32 bits at a time (the word size is
configured to 32 bits) the transfer would take:
8 bursts * [(4 cycles/word * 8 words/burst) + 1] = 264 cycles
Direct Memory Access (DMA) Module
732
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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