Analog Devices ADSP-BF506F Hardware Reference Manual page 1129

System Reset and Booting
An init block can consist of multiple sections where multiple boot blocks
represent the initcode within the boot stream. Only the last block has the
bit set.
BFLAG_INIT
The elfloader utility ensures that the last of these blocks vectors to the
initcode entry address. The utility instructs the on-chip boot ROM to exe-
cute a instruction to the given target address.
CALL
When the on-chip boot ROM detects a block with the bit set,
BFLAG_INIT
it boots the block into Blackfin memory and then executes it by issuing a
to its target address. For this reason, every initcode must be termi-
CALL
nated by an instruction to ensure that the processor vectors back to
RTS
the on-chip boot ROM for the rest of the boot process.
Sometimes initcode boot blocks have no payload and the field
BYTE COUNT
is set to zero. Then the only purpose of the block may be to instruct the
boot kernel to issue the instruction.
CALL
Initcode routines can be very different in nature. They might reside in
ROM or SRAM. They might be called once during the booting process or
multiple times. They might be volatile and be overwritten by other boot
blocks after executing, or they might be permanently available after boot
time. The boot kernel has no knowledge of the nature of initcodes and has
no restrictions in this regard. Refer to Loader and Utilities Manual for how
this feature is supported by the tools chain.
It is the user's responsibility to ensure that all code and data sections that
are required by the initcode are present in memory by the time the
initcode executes. Special attention is required if initcodes are written in
C or C++ language. Ensure that the initcode does not contain calls to the
runtime libraries. Do not assume that parts of the runtime environment,
such as the heap are fully functional. Ensure that all runtime components
are loaded and initialized before the initcode executes.
ADSP-BF50x Blackfin Processor Hardware Reference 24-25