Basic embedded concepts

1. Modern computer architecture

Three primary keys ：CPU, Memory module , Hard disk

2. Some processor concepts

cpu： a central processor , stay PC It is an independent chip .
MPU (Microprocessor Unit) Microprocessor , The central processing unit in microcomputer （CPU） It's called a microprocessor （MPU）
mcu It's a microcomputer , SCM is similar to

1. CPU(Central Processing Unit)：
   a central processor , stay PC It is an independent chip .
   In embedded systems , It is a unit in the chip , With other modules, such as USB、UART、 Audio constitutes a chip .
2. MPU(Mircro Processor Unit)：
   Microprocessor unit , Its function is equivalent to that in PC The use of CPU, It is just a processor , Need to match memory 、Flash And other peripherals can be used .
   Now? , Except on personal computers CPU, Basically can't find MPU 了 . And we usually don't put the on the computer CPU As MPU, After all, it is also quite big , Does not “ small ”.
3. MCU(Micro Controller Unit)：
   Microcontroller unit , Sometimes it is also called SCM .cpu+ram+flash（rom） etc.
   MCU The processor and various modules are integrated inside , such as USB controller 、UART controller 、 Memory 、Flash wait . Only a small number of external devices are needed , You can build an electronic system .
   C51 chip 、STM32 Wait for the chip , All are MCU.
   MCU Memory inside the chip or Flash, What is the capacity KB、 A few hundred KB、 A few MB The magnitude of , Generally, external memory or Flash.
   
4. Application Processors： Application processor
   The main chip in the mobile phone follows MCU similar , It also integrates processors and various modules .** But its performance has been greatly improved , You can connect several outside GB Of memory 、 A few GB Of Flash.** You can run the operating system
   In the cell phone , This main chip is generally used to process display 、 Input , Run the user's program , So call it “Application Processors”.
   “Application Processors” The concept of can be extended to other scenarios , No longer limited to mobile phones .
   

Follow MCU Compare ,Application Processors There are the following differences ：
a. More modules are integrated ：
Application Processors More modules are integrated inside , For example, for data processing DSP、 For graphic display GPU, There are even multiple processors .
Here is another concept “ System on chip ”(SoC,System on Chip),SoC The original intention of is to build a complete system on one chip .
But this concept is relatively broad in daily use ：MCU Chips can also be called SoC,Application Processors It can also be called SoC, Even if they have to be connected to external memory /Flash And other peripherals can operate .
In previous documents SoC when , It means a more complex system ; Now MCU Do not belong to SoC, because MCU Relatively simple . But the times are developing ,MCU It's getting more and more complicated , So the MCU As well as SoC It's OK, too .
In the circuit board of mobile phone , The available space is very small .Application Processors It can only be used with memory chips , Therefore, a kind of technology called package-on-package (PoP) Technology of ： Weld on the circuit board first Application Processors, stay Application Processors Then solder the memory chip on it , namely 2 The chips are stacked together .

b. The operating system is different ：
MCU Generally, the operating system is not running , Or run some small real-time operating systems with less resource consumption (RTOS).
MCU It is generally used to deal with things with high real-time requirements , Deal with some simple things .
Application Processors Basically, they will run more complex operating systems ( such as Linux), Run multiple on the operating system APP.

3. The concept of embedded system

One sentence leads to the whole embedded system : Support multiple device startup

ROM read-only
RAM Can read but write