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DX
FSX
CLKX
DR
FSR
CLKR
Element 4
Element 3
Element 2
Element 1
DXR-to-XSR copy
DXR-to-XSR copy
DXR-to-XSR copy
DXR-to-XSR copy
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RBR-to-DRR copy
RBR-to-DRR copy
RBR-to-DRR copy
RBR-to-DRR copy
Architecture
1207
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
Table 25-9. Receive/Transmit Element Length Configuration
(R/X)WDLEN1/2
Element Length (Bits)
000
8
001
12
010
16
011
20
100
24
101
32
110
Reserved
111
Reserved
25.2.5.5.4 Data Packing Using Frame Length and Element Length
The frame length and element length can be manipulated to effectively pack data. For example, consider
a situation in which four 8-bit elements are transferred in a single-phase frame, as shown in
.
In this case:
•
(R/X)PHASE = 0, indicating a single-phase frame
•
(R/X)FRLEN1 = 000 0011b, indicating a 4-element frame
•
(R/X)WDLEN1 = 000b, indicating 8-bit elements
In this example, four 8-bit data elements are transferred to and from the McBSP by the CPU or the EDMA
controller. Four reads of DRR and four writes of DXR are necessary for each frame.
Figure 25-11. Single-Phase Frame of Four 8-Bit Elements
The example in
can also be viewed as a data stream of a single-phase frame of one 32-bit
data element, as shown in
. In this case:
•
(R/X)PHASE = 0, indicating a single phase frame
•
(R/X)FRLEN1 = 0, indicating a 1-element frame
•
(R/X)WDLEN1 = 101b, indicating 32-bit elements
In this example, one 32-bit data element is transferred to and from the McBSP by the CPU or the EDMA
controller. Thus, one read of DRR and one write of DXR is necessary for each frame. As a result, the
number of transfers is one-fourth that of the previous example (
). This manipulation reduces
the percentage of bus time required for serial port data movement.