GXemul

Transcription

Suddenly, the music changes. Hi everyone, Though it should be obvious by now, I am creating an emulator in this video. I will try to provide some interesting commentary, so you can better understand what's going on in this video. In the case that you have never bothered to learn how something that is called a 'CPU' works, I will explain it briefly from a programmer's viewpoint. A CPU (Central Processing Unit) is a device that does the following; Step 1: Read an instruction from system memory. The instruction is a numeric value that simply represents an instruction in a manner specified by the CPU's makers. Step 2: Execute the instruction. An instruction might be, for example, 'Add two values together' or 'Read the next instruction from another location' Step 3: Go to step 1. Of course, this was a simplification. There is more to it, but this explains what happens in the code you see on the screen right now. Many of these operations deal with converting numbers to another format, or applying mathematical transformations to them. These shifts, for example, divide or multiply a value by two. Many of simpler programmers have never heard of a concept called 'delay slot'. A delay slot is a CPU feature, where a branch operation is indeed observed by the CPU, but it doesn't take effect immediately. Instead, the CPU processes one or more intermediate instructions first, and /then/ jumps to the address indicated much earlier. The MicroBlaze has one delay slot, but many branch instructions come with a delay slot option. The operation may be delayed, or it may be immediate. The are memory access operations (loading and storing) for different sizes of data. On this architecture, all of them access 32 bits at once, even if they use only a part of it. With MicroBlaze, there are some exceptionally large number of configuration options, that affect what the processor can do and what it cannot do. My emulator implements some of these features listed here, below, or will soon anyway. Sometimes, quite often really, a device attached to the computer requires immediate attention by the operating system running in the computer. This attention request is called an 'interrupt'. When the aptly named interrupt happens, the CPU interrupts whatever it was doing and begins running a code from a special location, where the operating system creators have placed the code to serve the interrupt. When that issue is dealt with, the CPU resumes what it was doing before the interrupt. An example of a matter requiring urgent attention might be when the user moves the mouse cursor and the operating system must let the window system know, so that it can draw the mouse cursor in another spot on the screen. The memory management unit is the core concept behind what makes the processor able to run modern operating systems. With the memory management unit, it is possible to control which areas of memory the programs can read, write or execute and which cannot. It is also what makes techniques like swapping possible. [quiet] Suddenly, music changes again.