AN2108 Freescale Semiconductor / Motorola, AN2108 Datasheet - Page 6

• Manufacturer Part Number: AN2108
• Description: AN2108 Programming the DSP56307/DSP56311 EFCOP in C Using Taskings Tool Suite
• Manufacturer: Freescale Semiconductor / Motorola

6
EFCOP Overview
After the EFCOP has been triggered to begin filtering:
Figure 3 depicts the EFCOP operational model, and Figure 4 shows how data is stored in the EFCOP.
Input data samples are fed into the EFCOP to trigger it
into calculating output samples.
The input samples can be transferred from a separate
buffer in memory or from a memory-mapped peripheral
register (for example, A/D converter). Input samples
can be transferred one, two, three, or four words at a
time, since the FDIR is four words deep. The EFCOP
automatically stores these input samples in the FDM
buffer, which is essentially a circular buffer of length N.
This ensures that the EFCOP has access to the N
most recent data samples, which are required to calcu-
late the corresponding output sample.
The output sample is placed into the output register.
Once an output sample is available in the FDOR, it
must be read from the FDOR and can then be stored in
memory or sent to a memory-mapped peripheral regis-
ter (for example, a D/A converter). Data transfers to
and from the EFCOP are initialized using polling, DMA,
or interrupts. These methods for transferring samples
from memory to the FDIR and from the FDOR to mem-
ory are discussed in Section 4 .
It is also important to note the location of the data sam-
ples and filter coefficients in the EFCOP memory
banks. Figure 4 represents both memory banks at an
arbitrary time, k , where x ( k ) is the most recent input
sample, w
length. Note that for the next iteration, FDBA will have
advanced by one word, and the filtering calculation will
involve a wrap-around. Therefore, the value held in
FDBA varies as time progresses.
NOTE: The EFCOP manages the value of FDBA and
the placement of data samples in FDM. The program-
mer need only be concerned with feeding values to the
FDIR
i
are the filter coefficients and N is the filter
Table 2. Overview of Steps in Programming the EFCOP and Its Registers
Step
Programming the DSP56307/DSP56311 EFCOP in C
Freescale Semiconductor, Inc.
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Filter Data Input Register (FDIR)
Filter Data Output Register (FDOR)
Filter Data buffer Base Address (FDBA)
Register