Bootstrap Control Logic; Bootstrap Program - Motorola DSP56156 Manual

Serial Interface SSI0. No access is provided to the bootstrap ROM other than through the
bootstrap process. Control logic will disable the bootstrap ROM during normal operations.
3.1.2.2

Bootstrap Control Logic

The bootstrap mode control logic is activated when the DSP is placed in one of the boot-
strap modes, Mode 0 or Mode 1. The control logic maps the bootstrap ROM into program
memory space until the bootstrap program changes operating modes when the bootstrap
load is completed.
When the DSP exits the reset state in Mode 0 or 1, the following actions occur:
1. The control logic maps the bootstrap ROM into the internal DSP program
memory space starting at location P:$0000. All program fetches during
the bootstrap operation are from the bootstrap ROM.
2. The control logic forces the entire internal program RAM space to be
write-only memory during the bootstrap loading process. All write
operations during the bootstrap program execution are to the PRAM.
3. Program execution begins at location $0000 in the bootstrap ROM. The
bootstrap ROM program performs the load of the internal program RAM
(PRAM) through either the memory expansion port from a byte-wide
external memory, through the Host Interface, or through the
Synchronous Serial Interface SSI0.
4. Upon completing the program RAM load, the bootstrap program
terminates the bootstrap operation by entering Operating Mode 2
(writing to the OMR) and by branching to the internal program RAM
location P:$0000. During the execution of the branch to P:$0000, the
bootstrap ROM is disabled and fetches from the PRAM are re-enabled.
The bootstrap mode may also be selected by setting the OMR bits for Operating Mode 0
or 1. This initiates a timed operation to map the bootstrap ROM into the program address
space after a delay to allow execution of a single instruction and a jump to P:$0000 to start
executing the bootstrap program. This technique allows the user to reboot the internal
PRAM (with a different program if desired).
3.1.2.3

Bootstrap Program

The bootstrap ROM contains the bootstrap firmware program that performs initial loading
of the DSP's internal program RAM (see Appendix A for a listing of the bootstrap code).
The program is written in DSP56100 core assembly language. It contains three separate
methods of initializing the PRAM: loading from a byte-wide memory starting at location
MOTOROLA OPERATING MODES AND MEMORY SPACES
RAM MEMORY DESCRIPTION
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