The data is oversampled and pulse shaped before passing it on to the RF module. Thus, the
aims of the DSP implemented in software comprise:
1. Initialization of interfaces and interrupts.
2. Initialization of CPLD, PLL, ADC, and DAC. These are done via McBSP.
3. Reception and transfer of data from=to the microcontroller. This is performed over
the HPI.
4. Formation of tag command data frames.
5. Mapping from bytes to symbols. The bit stream is converted into amplitude
modulated (AM) symbols, whereby here an AM mode is employed, although
other modulation modes are possible.
6. Pulse shaping. The symbol stream is moderately oversampled by a factor of 2,
which is required as a minimum by the subsequent mixer hardware, and ?¬?ltered
by a root raised cosine ?¬?lter.
7. Passing data samples to the RF module. The oversampled and pulse-shaped signal
values are passed over to the DAC, and its output is connected to the mixer??™s
input.
8. Reception of I and Q data from ADC. The inphase and quadrature signal values
are received from the ADC via the McBSP=CPLD. These samples are oversampled
by a factor of 4 compared with the symbol rate to permit suf?¬?cient resolution for
timing synchronization.
Steps 1 and 2 are performed at boot level. Initialization of PLL, ADC, and DAC needs to
be done via the McBSP after the CPLD is initialized and functional.
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