Learning ARM bare metal is a complicated matter, and the conceptual and basic knowledge of the introduction must be understood in order to facilitate the understanding of the latter knowledge.
ARM concept
ARM was first and foremost a company that designed CPUs and licensed them to various CPU manufacturers, so ARM is a CPU design company. At the same time, ARM is also the abbreviation of the CPU series designed by ARM.
ARM version distinction
The ARM version number can be divided into three categories:
· Kernel version number, such as ARMv5, ARMv7, ARMv7a, ARMv8a...
· Soc version number, such as Cortex-A8, Cortex-A9...
· Chip models, such as 2410, 2440, 6410, S5PV210...
Soc
Soc is short for System on Chip, the system on chip. Soc mainly includes a CPU central processor and various peripheral modules. The CPU and peripherals are placed in one chip through an integrated circuit.
There is no pure CPU now, it is SoC.
The core that ARM sells is actually the CPU (of course, the bus is also needed), and various peripherals are added by the semiconductor manufacturers themselves.
The difference between microcontroller and embedded
Platform difference:
The mainstream MCU platforms are 51, PIC, STM32, AVR, MSP430,
The mainstream embedded platforms are ARM, PPC, MIPS
Resources, prices, application areas
The resources of the single-chip chip are limited, the price is low, and the application fields are mostly small household appliances and terminal equipment.
The embedded on-chip resources are abundant, the price is high, and the application fields are wide, which can be basically applied to any field.
Development model
Microcontrollers are generally developed in bare metal, and the program size is small. RTOS will only be used on relatively high-end chips.
Embedded development generally uses embedded systems
Technical characteristics
The MCU mainly uses the C language and simple assembly, and the C language and the standard C are slightly different, and the advanced features of the C language are rarely used.
Embedded is more complex, generally layered design and development, divided into the underlying, application layer, different books may use different development languages, such as C + + and Java, more advanced features of C language
CPU design principle and bus
The CPU mainly includes an arithmetic unit, a controller, and a memory connected to the flash and the memory through a bus.
The bus is similar to the road in the CPU. The data is transferred between the CPU and the peripheral through the bus. The CPU is also connected to other peripherals in the SOC through the internal bus. For example, the UART device has an internal anti-interference capability due to the internal bus. , the operation speed is faster.
There are two types of buses: address bus and data bus:
The address bus is used to transfer the address. The CPU is addressed by the address bus, telling the device which address the data to fetch. The number of bits in the address bus determines the addressing range.
The data bus is used to transfer data. The CPU exchanges information with the outside through the data bus, and sends the data required by the device to the other party through the bus. The number of bits of the data bus determines the amount of information that can be exchanged by the CPU for one single communication.
The speed of the bus determines the speed at which the CPU and peripherals exchange information.
The address bus of the CPU and the number of bits of the data bus can be different, and the number of bits of the CPU refers to the number of bits of the data bus.
The 32-bit CPU has an address range of 4G, so it supports up to 4G of memory. The data bus is 32-bit. The efficiency of transmitting an int and transferring a char is the same.
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