Analog Devices VisualDSP++ 3.5 Manual page 225

Memory Overlays and Advanced LDF Commands
the transfer to complete (if necessary) and then executes the overlay func-
tion. If the symbol is set for load, the core returns to the instructions
immediately following the location of the function load reference.
Every overlay function call requires initializing the load/execute flag
buffer. Here, the function calls are delayed branch calls. The two slots in
the delayed branch contain instructions to initialize the flag buffer. Regis-
ter is set to the value placed in the flag buffer, and the value in
P0
stored in memory;
each overlay function call, the load buffer must be updated.
The following code (set for Blackfin processors) is from the main FFT
subroutine. Each of the four function calls are execution calls so the
pre-fetch (load) buffer is set to zero. The flag buffer in memory is read by
the overlay manager to determine whether the function call is a load or an
execute.
R0 = 0 (Z);
p0.h = prefetch;
p0.l = prefetch;
[P0] = R0;
call fft_first_2_stages;
R0 = 0 (Z);
p0.h = prefetch;
p0.l = prefetch;
[P0] = R0;
call fft_middle_stages;
R0 = 0 (Z);
p0.h = prefetch;
p0.l = prefetch;
[P0] = R0;
call fft_next_to_last;
R0 = 0 (Z);
p0.h = prefetch;
p0.l = prefetch;
[P0] = R0;
call fft_last_stage;
VisualDSP++ 3.5 Linker and Utilities Manual
for 16-Bit Processors
indicates a load, and
1
indicates an execution call. At
0
is
P0
5-19