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Instruction Overview
The
,
LOOP
LOOP_BEGIN
user friendly. The
more compact form.
If
is nonzero when the fetch address equals
LCn
ments
and places the address in
LCn
executes once through because
loop.
There are two special cases for small loop count values. A value of 0 in
causes the hardware loop mechanism to neither decrement or
Loop_Count
loopback, causing the instructions enclosed by the loop pointers to be exe-
cuted as straight-line code. A value of 1 in
loop mechanism to decrement only (not loopback), also causing the
instructions enclosed by the loop pointers to be executed as straight-line
code.
In the instruction syntax, the designation of the loop counter–
determines which loop level is initialized. Consequently, to initialize
, code
Loop0
LC0
In the case of nested loops that end on the same instruction, the processor
requires
Loop0
loop. The user is responsible for meeting this requirement.
For example, if
loop and loop 0 the outer loop.
Just like entries in any other register, loop register entries can be saved and
restored. If nesting beyond two loop levels is required, the user can explic-
itly save the outermost loop register values, re-use the registers for an inner
loop, and then restore the outermost loop values before terminating the
inner loop. In such a case, remember that loop 0 must always be outside of
loop 1. Alternately, the user can implement the outermost loop in soft-
ware with the Conditional Jump structure.
7-16
ADSP-BF53x/BF56x Blackfin Processor Programming Reference
,
LOOP_END
syntax contains the same information, but in a
LSETUP
Loop_Count
; to initialize
Loop1
to describe the outer loop and
, then the processor assumes loop 1 is the inner
LB0=LB1
syntax is generally more readable and
, the processor decre-
LBn
into the
. The loop always
LTn
PC
is evaluated at the end of the
Loop_Count
, code
.
LC1
Loop1
causes the hardware
or
LC0
LC1
to describe the inner
–
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