In the previous chapter we saw that the second operand of most arithmetic instructions can use a shift operator which allows us to shift and rotate bits. In this chapter we will continue learning the available indexing modes of ARM instructions. This time we will focus on load and store instructions.
ARM architecture has been for long targeted at embedded systems. Embedded systems usually end being used in massively manufactured products (dishwashers, mobile phones, TV sets, etc). In this context margins are very tight so a designer will always try to spare as much components as possible (a cent saved in hundreds of thousands or even […]
Control structures In the previous chapter we learnt branch instructions. They are really powerful tools because they allow us to express control structures. Structured programming is an important milestone in better computing engineering (a foundational one, but nonetheless an important one). So being able to map usual structured programming constructs in assembler, in our processor, […]
Branching Until now our small assembler programs execute one instruction after the other. If our ARM processor were only able to run this way it would be of limited use. It could not react to existing conditions which may require different sequences of instructions. This is the purpose of the branch instructions.
As we advance learning the foundations of ARM assembler, our examples will become longer. Since it is easy to make mistakes, I think it is worth learning how to use GNU Debugger gdb to debug assembler. If you develop C/C++ in Linux and never used gdb, shame on you. If you know gdb this small […]
We saw in chapter 1 and chapter 2 that we can move values to registers (using mov instruction) and add two registers (using add instruction). If our processor were only able to work on registers it would be rather limited.
Registers At its core, a processor in a computer is nothing but a powerful calculator. Calculations can only be carried using values stored in very tiny memories called registers. The ARM processor in a Raspberry Pi has 16 integer registers and 32 floating point registers. A processor uses these registers to perform integer computations and […]
In my opinion, it is much more beneficial learning a high level language than a specific architecture assembler. But I fancied learning some ARM assembler just for fun since I know some 386 assembler. The idea is not to become a master but understand some of the details of what happens underneath.