26.6. Comparison of Macro and Micro Program Execution

So, basically what we can do is that, we can actually write a micro routines which can be shared. For example, as I told you like add and sub. So, most of the case will be similar excepting 1 bit position or the 1 control signal corresponding to add or subtract of the ALU.

In this chunk, we introduce the concept of micro routines and macro instructions. Micro routines are small sequences of instructions that can perform operations like addition or subtraction. The key idea is that many of these routines can share a common structure, differing only slightly based on one or two control signals. For example, the micro routine for 'add' will be very similar to that for 'subtract', with minor differences in control signals.

Imagine you are following a recipe that requires you to either bake cookies or bake a cake. Both involve mixing ingredients, but you may change one or two steps depending on which dessert you're making (e.g., adding baking powder for cake). Here, 'baking cookies' and 'baking cake' represent micro routines sharing a common method.

Now, let us again now actual I will tell you two things, two things are very important over here.

This part emphasizes that understanding how macro instructions are executed through micro instructions is crucial. A macro instruction like 'jump on zero' will be translated into multiple micro instructions that detail each step involved in that jump operation. The importance is not just in how to perform a single instruction but how a complete macro instruction operates within the micro instruction set.

Think of a car's navigation system. In order to reach a destination (the macro instruction), the system provides step-by-step directions (micro instructions) on how to get there, such as turning left, continuing straight, etc. Each step is necessary to achieve the overall goal of reaching the destination.

Secondly, as I told you we also give some idea that how micro instructions can be macro instruct micro instructions corresponding to different type of similar macro instructions can be clubbed.

Here, we discuss the optimization of micro instructions, where similar macro instructions can be grouped together. This means that instead of writing separate micro routines for instructions that are close in function, we can create a shared micro routine that incorporates conditions based on which specific instruction is being executed. This reduces redundancy and improves efficiency.

This is like having a shared family recipe book where you note variations for similar dishes. For example, instead of having a separate recipe for chicken curry and vegetable curry, you can have one base recipe with variations to guide you based on what ingredients you have. This keeps your cooking more efficient.

So, this type of branching will be actually called the implicit jumps we have to do, because you are writing a common micro program for different macro program.

This segment introduces the concept of implicit jumps, which occur when a micro program needs to switch between different macro instructions. These implicit jumps are based on conditions determined by the current instruction being executed and may not be explicitly defined in the instruction set. In contrast, explicit jumps are clear commands written directly as part of the macro instructions.

Consider someone following a flowchart to solve a problem. There are clear paths to follow (explicit jumps) but also side paths that may be taken based on previous answers (implicit jumps). For instance, if one answer leads to a different question instead of following a straight line.

So, these are the control signals to be generated, this is the branch field address; that means, if you have to jump to some location that value will be given over here that will be loaded to the micro program control unit.

In this section, we explain the role of control signals in managing the flow of execution within a micro program. Control signals determine whether a jump occurs or whether the next instruction is simply executed sequentially. The branch address holds critical information about where to jump if needed, building the bridge between macro and micro instructions.

Imagine a train routing system. Control signals act like switches controlling which tracks the train should go to. Depending on the current position and upcoming signals (similar to control signals), it decides whether to continue on its current track or switch to another route.

So, if it is jump on 0 that is 0 flag is set then basically you have to load the program counter corresponding to this.

In this part, the importance of common elements in micro instructions is discussed. When a specific condition like 'jump on 0' is true, it influences the program counter, which directs the flow of control within the micro instruction framework. Understanding these conditions helps to grasp how different micro programs can interact.

Think of a traffic light system. When the light is green (like the jump condition being met), vehicles move (executing the next instructions). Understanding when to stop or go at intersections parallels how micro instructions react to control signals.

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