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Communication Processor Module
MOTOROLA
MPC823 USER’S MANUAL
16-29
DSP
COMMUNICATION
16
PROCESSOR
MODULE
16.3.2.1 HARDWARE. The RISC microcontroller’s hardware contains special DSP
processing units, such as a multiplier and accumulator that is capable of handling real or
complex numbers, and an address generator that can access cyclic buffer structures in
dual-port RAM.
16.3.2.2 SOFTWARE. Your software interfaces to the DSP via the function descriptor that
is described in system memory. The function descriptor defines the sequence and data flow
of your DSP task.
16.3.2.3 FIRMWARE. The RISC microcontroller’s firmware is a set of DSP functions that
have been compiled to form a library of basic building blocks and each function within the
library is implemented by a microcode routine stored in the internal ROM. In addition, a
software interface is defined that enables parameters to be passed between the core and
communication processor module. Several functions can be chained together to reduce
software intervention and interrupt rates, assuming that all data structures reside in the
dual-port RAM.
Table 16-6 lists the DSP functions that are included in the library.
16.3.3 Programming the DSP Functions
Similar to the SCC2 buffer descriptor, a function descriptor (FD), is used to specify the DSP
function and pass the parameters. A table of such descriptors forms a circular queue with a
programmable length. The descriptors are stored in external memory. There are two
function descriptor tables (also referred to as chains)—one for the transmitter and one for
the receiver. The core prepares a chain of function descriptors in the system memory and a
special host command notifies the RISC microcontroller when to execute the chain. A
maskable interrupt is generated once the chain is completed. As shown in
Figure 16-8, the
pointer to the transmit (TX) chain must be written into the FDBASE field of the DSP2
parameter RAM and the pointer to the receive (RX) chain must be written into DSP1.
Table 16-6. DSP Functions
FUNCTION
OPCODE
INPUT
COEFFICIENT
OUTPUT
APPLICATION
FIR1
00001
Real
Decimation, RX Interpolation
FIR2
00010
Complex
Real
Complex
TX Filter, RX Filter
FIR3
00011
Complex
Real/Complex
EC Computation, Equalizer
FIR5
00011
Complex
Real/Complex
Fractionally Spaced Equalizer
FIR6
00110
Real
Complex
—
IIR
00111
Real
Biquad Filter
MOD
01000
Complex
Real/Complex
TX Modulation
DEMOD
01001
Real
Complex
RX Demodulation
LMS1
01010
—
EC Update, Equalizer Update (T/2, T/3)
LMS2
01011
—
Equalizer Update (2T/3)
WADD
01100
Real
—
Real
Interpolation