36-30
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
36.17.3 WADD Applications
Table 36-29 shows the linear functions available using different
a
and
b
values.
36.18 DSP Performance Using the Core Alone Versus
Using the CPM
A DSP task on the MPC860 can be done with the core alone, or with the help of the built-in
DSP capabilities of the CPM. A V.32 modemÕs Tx data pump ßow is used for comparing
DSP performance using the core alone versus using the CPM. Figure 36-36 shows the Tx
Þlter example application, consisting of three subÞlters.
Figure 36-36. Example DSP ApplicationÑTx Filter
36.18.1 Tx Filter Example (Core Only)
Implementing the Þlter using the following C code on the core takes 476 instructionsÑ371
for the Þlter and 105 for the modulation. The transmission symbol rate requires running the
Þlter 2,400 times a second. Thus, implementing the Þlter in software alone requires the core
to execute 1.14 million instructions per second.
void tx_filter ()
{
S16 *coefr
S16 *samplr, *sampli
S16 *coefend;
S32 filtoutr, filtouti;
U8 subcount, sampleindex;
extern S16 mult(S16 p1, S16 p2); /* in-line invocation */
coefr=txfiltcoef_str;
coefend=txfiltcoef_end;
samplr=&txfiltdly[REAL][txfiltptr];
Table 36-29. WADD Applications
a
b
Function
0
£ a £
1
1-
a
Linear interpolation.
a
0
y(n)=
a
x(n) scalar multiply.
1
-1
y(n)=x
1
(n)-x
2
(n) vector subtract.
MOD
1 INPUT / BAUD
3 OUTPUTS / BAUD
3 OUTPUTS / BAUD
Tx Filter
cos
w
nT, sin
w
nT
Содержание MPC860 PowerQUICC
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