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2920 SUPPORT TOOLS
X and Yare variable names. These equations are useful
for propagation and scaling of the digital signal between
stages.
These modules of assembly language code, for each pole
or zero, can be accumulated into a file to be used as
input to the 2920 Assembler. During code generation
for one stage of a filter, it may be desirable to sacrifice a
certain amount of numerical accuracy in order to get a
shorter program. Towards this end, code generation, is
performed subject to constraints which the user can
specify. One such constraint consists of piecewise linear
bounds on the gain, in decibels, as a function of fre-
quency. The Compiler then strives to minimize the
mean-square deviation from these bounds.
Before saving the resulting code into a file, designers
can interactively adjust the number of instructions or
the error constraint in order to achieve the shortest pro-
gram with a tolerable error. This new code can then be
saved into a file.
Filing And Retrieving Code Or Parameters-The
process described above, of specification, display, and
adjustment, is extremely interactive. The file commands
have been structured to facilitate the restart of an inter-
-:F1
SPAC20
SFT
rupted design or test session. They also make it easy to
accumulate, into one or many files, the partial results of
specifying parameters or creating code. Parameter files
saved from an interrupted design session can then be
included at a later date, to resume that design session
with all relevant variables restored to their condition at
the time the session was interrupted.
Compound Commands-SP AS20 contains macro
and compound command facilities which enable multi-
ple and conditional execution of command sequences,
including substitution of varying parameters. These
capabilities enable users to extend the language itself by
defining their own commands and constructs.
Such macros make it possible, for example, to define an
iterative process of moving poles and zeros and graph-
ing the resultant response without having to type all the
commands during each iteration of that process. Condi-
tional code generation and display could be included in
such a procedure. Macros and compound commands
are interruptable at any time via the console ESCape
key, should error or time constraints make that
desirable.
A sample SPAS20 session is shown in Figure 9-3.
ISIS-II 2HO SICNAL PROCESSING APPLICATIONS conPlLER.
VI
0
o
oDEFINE POLE I
•
-707.707
, CREATE A POLE IN CONTINUOUS S-PLANE
o
oP:
• LIST ALL POLES AND ZEROS
POLE
I
•
-707 00000.707 OOOOO.COHT IHUOUS
o
orSCALE •
100.10000
, EsaBL ISHES FREQUEHC\
RANCE OF
INTEREST
.
OY$C~LE
•
-4~.1
, ESTABLISHES nACHI TUDE HSPOHSE RANCE OF
INTEREST
.
oCR';PH CAIN
,
PLOT ftACNITUDE RESPONSE OF POLE
PAIR
CA IN
I 0
--------------------------
-:<
~
-~
"
...
.,
~
"':0
I)
- I l I
-H
;
-I
~
5
-13 -
-20
~
- l l I
-
2~
:<
-2"
'5
-z~
. , .
-] I
,
-H
J
- Jo;
l
-33 4
... 41j
to
... <4?
~
... 45 .,
DB I HZ
I
100
I~O
200
JOO 400 500
700 1000 1400 2000
3000
5000
10000
Figure
9-3.
Sample SPAS20 Session
9-5
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