NS32FV16 Datasheet, PDF (13/104 Pages) Texas Instruments – Advanced Imaging/Communication Signal Processors

2 0 Architectural Description (Continued)
Although memory is addressed as bytes it is actually orga-
Normally the linker program specifies the locations of the
nized as words Therefore words and double-words that are
three components The Static Data and Link Table typically
aligned to start at even addresses (multiples of two) are
reside in RAM the code component can be either in RAM or
accessed more quickly than words and double-words that
in ROM The three components can be mapped into non-
are not so aligned
contiguous locations in memory and each can be indepen-
2 2 1 Address Mapping
dently relocated Since the Link Table contains the absolute
addresses of external variables the linker need not assign
The NS32FX164 supports the use of memory-mapped pe-
absolute memory addresses for these in the module itself
ripheral devices and coprocessors Such memory-mapped
they may be assigned at load time
devices can be located at arbitrary locations within the
16-Mbyte address range available externally
To handle the transfer of control from one module to anoth-
er the NS32FX164 uses a module table in memory and two
Addresses marked as Reserved in Figure 2-15 are not avail-
registers in the CPU
able in the present implementation of the NS32FX164 and
should not be used The top 8-Mbyte block is reserved by
National Semiconductor Corporation and only a few loca-
tions within this block are presently used to access the on-
chip RAM array and DSP Module registers Figure 2-15
shows the NS32FX164 address mapping
Start Address
(HEX)
00000000
Memory and I O
00FFFE00
Interrupt Control
te ^01000000
Reserved
FFFE0000
DSPM Internal RAM
FFFE1000
Reserved
FFFF8000
DSPM Dedicated Registers
FFFF8028
Reserved
le ^FFFF9000
DSPM Control Status Registers
FFFF9014
Reserved
FIGURE 2-15 NS32FX164 Address Mapping
2 3 MODULAR SOFTWARE SUPPORT
The NS32FX164 provides special support for software mod-
o ^{ules and modular programs}
Each module in a NS32FX164 software environment con-
sists of three components
1 Program Code Segment
s This segment contains the module’s code and constant
data
2 Static Data Segment
Used to store variables and data that may be accessed
by all procedures within the module
b 3 Link Table
This component contains two types of entries Absolute
Addresses and Procedure Descriptors
An Absolute Address is used in the external addressing
mode in conjunction with a displacement and the current
O ^{MOD Register contents to compute the effective address}
The Module Table is located within the first 64 kbytes of
memory This table contains a Module Descriptor (also
called a Module Table Entry) for each module in the ad-
dress space of the program A Module Descriptor has four
32-bit entries corresponding to each component of a mod-
ule
 The Static Base entry contains the address of the begin-
ning of the module’s static data segment
 The Link Table Base points to the beginning of the mod-
ule’s Link Table
 The Program Base is the address of the beginning of the
code and constant data for the module
 A fourth entry is currently unused but reserved
The MOD Register in the CPU contains the address of the
Module Descriptor for the currently executing module
The Static Base Register (SB) contains a copy of the Static
Base entry in the Module Descriptor of the currently execut-
ing module i e it points to the beginning of the current
module’s static data area
This register is implemented in the CPU for efficiency pur-
poses By having a copy of the static base entry or chip the
CPU can avoid reading it from memory each time a data
item in the static data segment is accessed
In an NS32FX164 software environment modules need not
be linked together prior to loading As modules are loaded
a linking loader simply updates the Module Table and fills
the Link Table entries with the appropriate values No modi-
fication of a module’s code is required Thus modules may
be stored in read-only memory and may be added to a sys-
tem independently of each other without regard to their in-
dividual addressing Figure 2-16 shows a typical
NS32FX164 run-time environment
2 4 INSTRUCTION SET
2 4 1 General Instruction Format
Figure 2-17 shows the general format of a Series 32000
instruction The Basic Instruction is one to three bytes long
and contains the Opcode and up to two 5-bit General Ad-
dressing Mode (‘‘Gen’’) fields Following the Basic Instruc-
tion field is a set of optional extensions which may appear
depending on the instruction and the addressing modes se-
of an external variable belonging to another module
lected
The Procedure Descriptor is used in the call external pro-
cedure (CXP) instruction to compute the address of an
external procedure
Index Bytes appear when either or both Gen fields specify
Scaled Index In this case the Gen field specifies only the
Scale Factor (1 2 4 or 8) and the Index Byte specifies
which General Purpose Register to use as the index and
which addressing mode calculation to perform before index-
ing
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