简单整理了一些嵌入式底层CPU相关的概念。
# CPU
CU. Control Unit. send need-clac-data -> ALU clac -> get result send back -> to save in memory
ALU Arithmetic Logic Unit. Binary clac, such as add/sub/mult(except interger division)
MMU. Memory Management Unit. registers like: MAR MDR PC AC CIR
- MAR. Memory adress register. save will-be-visited-data 's address
- MDR. Memory data register. saveor will-write-in-RAM data or from-RAM-data
- PC. Program Counter. save next-exe-instruction 's address
- AC. Accumulator. save ALU and CU 's middle-result data
- CIR. Current Instruction Register. save current executing instruction
# Bus types
数据总线DB. Data Bus. 传输数据. CPU -- RAM 来回传数据 双向
地址总线AB. Address Bus 传输地址. 指定RAM中存储数据的地址
控制总线CB(系统总线). Control Bus 传输命令(控制信号和时序信号). 将CU的信号传至周边设备
扩展总线. Expansion Bus 计算机和外部设备通信的总线，如ISA PCI(现在已经进化为PCIe)
# Bus tech indicators
Band 单位时间内总线上传送的数据量
Bit 总线能同时传送的二进制数据的位数，like 32位/64位
Working Freq: MHZ为单位
# RAM "random access memory"
SRAM. cpu cache, don not need to reflesh
DRAM. keep reflesh save data
SDRAM. keep reflesh, quick speed, large capacity
DDR SDRAM. dual channal
# ROM "read-only memory"
1.几K到几十K byte的ROM. 存储刚上电时对cpu和一些核心外设进行初始化的代码
2.NOR FLASH. 1M~4M，存放代码，可以由CPU直接取指并执行
3.NAND FLASH. 存放程序/数据，需要CPU加载到内存中使用
# Core peripheral
初始化code存放在ROM中，CLOCK, serial port, MMU, DRAM, FLASH