3.4.2 Bursting Peripherals
External
peripheral
9001 0000h
...1_2..1_1..0_2..0_1
EVTx
479_640
478_640
477_640
478_639
479_639
479_638
...
...
...
...
...
...
2_640
...
...
1_639
1_640
0_640
0_639
0_638
...
...
...
...
...
...
...
...
0_3
0_2
1_2
1_1
0_1
2_1
478_1
479_1
477_1
479_2
478_2
479_3
A000 0000h
A000 0500h
A000 0A00h
...
...
A009 5100h
A009 5600h
A009 5B00h
Peripheral Servicing Example
www.ti.com
Higher bandwidth applications require that multiple data elements be presented to the CPU for every
synchronization event. This frame of data can either be from multiple sources that are working
simultaneously or from a single high-throughput peripheral that streams data to/from the CPU.
In this example, a port is receiving a video frame from a camera and presenting it to the CPU one array at
a time. The video image is 640
×
480 pixels, with each pixel represented by a 16-bit element. The image
is to be stored in external memory.
shows this example.
To transfer data from an external peripheral to an external buffer one array at a time based on EVT
n
,
channel
n
must be configured. Due to the nature of the data (a video frame made up of arrays of pixels)
the destination is essentially a 2D entity.
shows the parameters to service the incoming data
with a 1D-to-2D transfer using AB-synchronization. The source address is set to the location of the video
framer peripheral, and the destination address is set to the start of the data buffer. Since the input address
is static, the SRCBIDX is 0 (no modification to the source address). The destination is made up of arrays
of contiguous, linear elements; therefore, the DSTBIDX is set to pixel size, 2 bytes. ANCT is equal to the
pixel size, 2 bytes. BCNT is set to the number of pixels in an array, 640. CCNT is equal to the total
number of arrays in the block, 480. SRCCIDX is 0 since the source address undergoes no increment. The
DSTCIDX is equal to the difference between the starting addresses of each array. Since a pixel is 16 bits
(2 bytes), DSTCIDX is equal to 640
×
2.
Figure 3-9. Servicing Peripheral Burst Example
EDMA3 Transfer Examples
74
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Summary of Contents for TMS320DM357
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