Data Packing Using Frame Length and Word Length
11-3
Data Packing Examples
SPRU592E
Two 16-bit data words are transferred to and from the McBSP by the CPU or
by the DMA controller. Therefore, two reads, from DRR2 and DRR1, and two
writes, to DXR2 and DXR1, are necessary for each frame. This results in only
half the number of transfers compared to the previous case. This manipulation
reduces the percentage of bus time required for serial port data movement.
Note:
When the word length is larger than 16 bits, make sure you access
DRR2/DXR2 before you access DRR1/DXR1. McBSP activity is tied to
accesses of DRR1/DXR1. During the reception of 24-bit or 32-bit words,
read DRR2 and then read DRR1. Otherwise, the next RBR[1,2]-to-DRR[1,2]
copy occurs before DRR2 is read. Similarly, during the transmission of 24-bit
or 32-bit words, write to DXR2 and then write to DXR1. Otherwise, the next
DXR[1,2]-to-XSR[1,2] copy occurs before DXR2 is loaded with new data.
Figure 11
−
2.One 32-Bit Data Word Transferred To/From the McBSP
DRR2 copy
RBR2 to
DRR1 copy
RBR1 to
DXR0 to XSR0
copy
DXR1 to XSR1
copy
Word 1
CLKR
FSR
DR
CLKX
FSX
DX
Содержание TMS320VC5509
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