Analog Devices VISUALDSP++ 3.5, Руководство пользователя

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ADSP-219x DSP Booting
3-14 Vi+ Loader Manual
for 16-Bit Processors
The data segment
seg_ext_data
is defined by the
TYPE(DM)
command,
which sets the logical width to 16 bits. Since the
WIDTH(16)
command also
sets the physical width to 16 bit, no data packing and no address multiply
is required. Logical addresses are equal to physical EPROM addresses in
this special case. The 16-bit EPROM image generated by the loader is
described in
Table 3-2 :
!
The DSP cannot access off-chip addresses lower than
0x010000
.
Typically this address space is accessed by taking advantage of
address aliasing. The memory strobe (
/MS0
) covers an address range
from
0x010000
to
0x400000
. For example, if the EPROM size is less
than 4M words and the EPROM is the only device connected to
/MS0
, the first 64K words can be accessed through addresses
0x200000
to
0x20FFFF
.
If a project consists only of two segments (
seg_ext_data
and
seg_ext_code
), a 128K x 16-bit EPROM device would be sufficient to
store all the required data and instructions. If the loader utility is invoked
with the
-maskaddr 17
switch ( on page 3-22 ), all physical address bits
greater than or equal to
A17
are masked out. The loader ANDs all physical
addresses with
0x01FFFF
. The resulting EPROM image maps segment
seg_ext_code
into the unused space below
0x010000
(see Table 3-3 ).
This way, a 128K x 16-bit EPROM can be burned properly. At runtime,
seg_ext_code
aliases back to the addresses above
0x020000
when address
lines
A17
through
A21
are not connected.
Table 3-2. EPROM Image Description
Address range Purpose
0x000000–0x00FFFF
Not used
0x010000–0x01FFFF
seg_ext_data
0x020000–0x02FFFF seg_ext_code