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Figure 15.1 shows the programming model of an 80x86 processor running in real mode. The integer registers are identical to those presented in Chapter 14. In fact, they are saved and restored using the same technique. The only difference between this port and the one presented in Chapter 14 is that we also need to save and restore the FPU registers which is done by using the context switch hook functions.
Development Tools
As in the section 80x86 Port with Emulated FP Support, I used the Borland C/C++ V4.51 compiler along with the Borland Turbo Assembler for porting and testing. This compiler generates reentrant code and provides in-line assembly language instructions that can be inserted in C code. The compiler can be directed to generate code specifically to make use of the FPU. I tested the code on a 300 MHz Pentium-II-based computer running the Microsoft Windows 2000 operating system. In fact, I configured the compiler to generate a DOS executable which was run in a DOS window.
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Table 15.1 shows the Borland C/C++ compiler V4.51 options (i.e., flags) supplied on the command line. These settings were used to compile the port as well as example 4 provided in Chapter 1.Table 15.1, Compiler options used to compile port and examples.
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Table 15.2 shows the Borland Turbo Assembler V4.0 options (i.e., flags) supplied on the command line. These settings were used to assemble OS_CPU_A.ASM.
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