13 Hardware Examples
13 – 2
13.2
BOOT LOADING FROM HOST USING BUS REQUEST & GRANT
All ADSP-2100 family processors that have internal program memory
RAM support boot loading. With boot loading, the processor reads
instructions from a byte-wide external memory device (usually an
EPROM) over the memory interface and stores the instructions in the 24-
bit wide internal program memory. Once the external memory device is
set up to provide bytes in the proper order, the boot operation can run
automatically and transparently at reset or when forced in software. See
Chapter 10, “Memory Interface.”
In some systems where the ADSP-21xx is controlled by a host processor, it
is necessary to boot the DSP directly from the host. In this case the host,
rather than an EPROM, is the source of bytes to be loaded into on-chip
memory. If the ADSP-21xx has a host interface port (such as the ADSP-
2111), it can perform automatic boot loading through this port. If the
processor does not have a host interface port, however, it can still boot
through the memory interface using the bus request signal, as described
below.
This example shows a simple way to download programs from a host
processor to the internal program memory of an ADSP-21xx. There are
several techniques for connecting a DSP processor to a host. The choice of
which technique to use depends upon the I/O structure of the host,
availability of I/O port lines, and the amount of address decoding logic
already available in the system.
Figure 13.1 illustrates a minimal system implementation to allow a
microcontroller to boot an ADSP-21xx. The only hardware required is a D-
type flip-flop and a 5 k
Ω
resistor. The resistor is used to pull the ADSP-
21xx’s
BMS
pin (Boot Memory Select) high.
The ADSP-21xx automatically enters its booting sequence after the
processor is reset (when the MMAP pin is tied low) or when software
initiates a reboot operation. When the ADSP-21xx begins to fetch a byte
from external boot memory (in this case, the host processor), it asserts
BMS
. When
BMS
goes low, the flip-flop is preset and the
Q
output
brought low. This low signal asserts
BR
(bus request) on the ADSP-21xx.
When bus request is recognized by the ADSP-21xx, the current execution
cycle is allowed to finish and then processor operation is suspended. The
ADSP-21xx then asserts
BG
(bus grant) in the next cycle (after
BR
is
recognized).