Special Function Group - Lucent Technologies DSP1617 Information Manual

Information Manual
April 1998
4.5 Instruction Set

4.5.4 Special Function Group

Instructions from the special function group are always executed in one instruction cycle. They require one word of
program memory. The special function instructions are used to implement a number of algorithms that include the
following nonlinear functions: absolute value, signum, minimum and maximum value finder, A-law and µ-law con-
versions, division, half-wave and full-wave rectification, and rounding. Special function instructions are executed
either conditionally or unconditionally. Both the condition and its complement are available for use in special func-
tion instructions. Instructions from this group can be used in the cache.
The special function instructions can be conditioned on the basis of the flags defined in
most recent accumulator or BMU operation prior to the special function instruction establishes the state of the flags
for the conditions associated with logical or mathematical functions.
To write a special function instruction unconditionally, write F2 by itself (see
tion instructions conditionally, write the full form—if CON F2. To use the event counter, write ifc CON F2—mean-
ing:
if CON is true then
c1=c1+1
F2 instruction
c2=c1
}
else {
c1=c1+1
}
Note: If using the event counter (ifc instruction) and if the condition field CON is c0lt or c0ge, c0 is not incre-
mented. Otherwise, if using the event counter (ifc instruction) and if CON is c1lt or c1ge, c1 is incremented
once after the test. For example, ifc c0lt a0 = a1 first tests to see if c0 is less than zero, then increments
c1. If c0 is less than zero, a0 = a1 is executed and c2 is set to the new value of c1. If c0 is ≥0, no further
action occurs. Normally, a test of c0, such as if c0lt goto 0x400, increments c0. In the case of the ifc c0lt
F2 instruction, c0 is not incremented.
Lucent Technologies Inc.
DSP1611/17/18/27/28/29 DIGITAL SIGNAL PROCESSOR
(continued)
{
Special Function Instructions
DRAFT COPY
if CON F2
ifc CON F2
F2
Instruction Set
Table 4-3. The result of the
Table 4-10). To write the special func-
4-19