Analog Devices ADSP-BF53x Blackfin, Reference

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ADSP-BF53x/BF56x Blackfin Processor Programming Reference 4-23
Program Sequencer
Listing 4-1. Loop Example
P5 = 0x20 ;
LSETUP ( lp_start, lp_end ) LCO = P5 ;
lp_start: R5 = R0 + R1(ns) || R2 = [P2++] || R3 = [I1++] ;
lp_end: R5 = R5 + R2 ;
When executing an
LSETUP
instruction, the program sequencer loads the
address of the loop’s last instruction into
LBx
and the address of the loop’s
first instruction into
LTx
. The top and bottom addresses of the loop are
computed as PC-relative addresses from the
LSETUP
instruction, plus an
offset. In each case, the offset value is added to the location of the
LSETUP
instruction.
The
LC0
and
LC1
registers are unsigned 32-bit registers, each supporting
2
32
–1 iterations through the loop.
[
When
LCx = 0
, the loop is disabled, and a single pass of the code
executes. If the loop counter is derived from a variable with a range
that may include zero, it is recommended to guard the loop against
the zero case.
P5 = [P4];
CC = P5 == 0;
IF CC JUMP lp_skip;
LSETUP (lp_start, lp_end) LC0 = P5;
lp_start: ...
lp_end: ...
lp_skip: /* first instruction outside the loop */