Emulation is an attempt to imitate a device on a specific system. There are three ways to build emulators: dynamic and static recompilation and interpretation. To achieve the maximum speed effect when working, it is recommended to use all three methods. Let's consider an example of writing a typical processor emulator.
Instructions
Step 1
Select a programming language. The recommended and probably the only alternative is C and Assembler. In C, you can make code that will be ported to other platforms. It is relatively simple to understand and easy to debug, but much slower than others. The assembler is distinguished by its high speed of work, it uses processor registers, which contributes to the approximation of the program to the recompiling one. However, it is very difficult to track and fix codes in it. It is important to know the chosen language well and optimize the code well for speed.
Step 2
Assign an initial value to the cyclic and program counter. The cyclic counter counts the number of clock cycles after which the interrupt occurs, and the software PC shows the memory area in which the next opcode instruction lies.
Step 3
After you receive the opcode, subtract the number of clock cycles from the cyclical counter that it takes to execute the opcode. Please note that some commands differ in number of ticks depending on the arguments. For such commands, change the counter in the run code later.
Step 4
After successful execution of the opcode, check the need to trigger interrupts. At this point, complete the tasks that urgently need to be synchronized in time.
Step 5
Check each pass of the cycle for the need to complete its work. Remember that the program should be modular, since most computers are made up of modules, and a typical emulator should, if possible, be the same as the original system. This will provide faster and easier debugging of the program, and you can use the same modules for different emulators, because many computers are based on the same processor or video processor models.
