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NS32FX16-15 Datasheet(PDF) 11 Page - National Semiconductor (TI) |
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NS32FX16-15 Datasheet(HTML) 11 Page - National Semiconductor (TI) |
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11 / 88 page  20 Architectural Description (Continued) Address (Hex) 00000000 Memory and IO 00FFFE00 Interrupt Control 01000000 Address Not Available Off-Chip (Do Not Use) FF800000 Reserved FFFFD000 On-Chip RAM Array FFFFD200 Reserved FFFFD4XX DSP Module Reserved FFFFFFFF FIGURE 2-9 NS32FX16 Address Mapping 23 MODULAR SOFTWARE SUPPORT The NS32FX16 provides special support for software mod- ules and modular programs Each module in a NS32FX16 software environment consists of three components 1 Program Code Segment 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 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 MOD Register contents to compute the effective address of an external variable belonging to another module The Procedure Descriptor is used in the call external pro- cedure (CXP) instruction to compute the address of an external procedure Normally the linker program specifies the locations of the three components The Static Data and Link Table typically reside in RAM the code component can be either in RAM or in ROM The three components can be mapped into non- contiguous locations in memory and each can be indepen- dently relocated Since the Link Table contains the absolute addresses of external variables the linker need not assign absolute memory addresses for these in the module itself they may be assigned at load time To handle the transfer of control from one module to anoth- er the NS32FX16 uses a module table in memory and two registers in the CPU 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 ie 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 NS32FX16 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 2-10 shows a typical NS32FX16 run-time environment 11 |
Similar Part No. - NS32FX16-15 |
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Similar Description - NS32FX16-15 |
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