Read Synchronization Vs. Write Synchronization - Texas Instruments OMAP5912 Reference Manual

DSP DMA
4.13.1

Read Synchronization vs. Write Synchronization

Table 105. Read/Write Synchronization
Channel Synchronization Set by
DMA_CCR sync[4:0]
Not Equal to 00000
No
Yes
Yes
Yes
144 Direct Memory Access (DMA) Support
When a DMA channel is configured for synchronization, the synchronization
event is tied to the element read operation or the element write operation,
depending on the source and destination ports. There are three general cases
(see Table 105):
Case 1: Source port is peripheral; destination port is SARAM, DARAM,
-
EMIF, or MPUI.
The channel waits for the synchronization event before reading from the
peripheral port into the channel FIFO. Once the FIFO has filled, the DMA
channel begins writing to the destination port to empty the FIFO (source
synchronization).
Case 2: Source port is SARAM, DARAM, EMIF, or MPUI; destination port
-
is peripheral.
As soon as the channel is enabled (EN bit set) a read from SARAM port is
performed to feed the channel FIFO. The FIFO writes to the peripheral port
to not begin until the synchronization event is detected. When the channel
is operating in frame-synchronization mode (DMA_CCR_FS = 1), several
prereads can occur to the point of filling the FIFO while the channel is
awaiting the synchronization event (destination synchronization).
Case 3: Source port is SARAM, DARAM, EMIF, or MPUI; destination port
-
is SARAM, DARAM, EMIF, or MPUI.
The channel waits for the synchronization event before reading from the
source port into the channel FIFO. Once the FIFO has filled, the DMA
channel begins writing to the destination port to empty the FIFO (source
synchronization).
Source Port
X
Peripheral port
SARAM, DARAM,
EMIF, or MPUI port
SARAM,DARAM,
EMIF, or MPUI port
Destination Port
X
SARAM,DARAM,
EMIF, or MPUI port
Peripheral port
SARAM,DARAM,
EMIF, or MPUI port
Synchronization
Event Triggers
No synchronization
Source read
Destination write
Source read
SPRU755B