Unit4: CPU Architecture

Interrupts 中断信号：

• signal to stop CPU to figure out what to do next
• allow computer to multitasking 多任务 （不断的切换任务，模拟同时 ）

紧急任务需要处理 interrupt signal ， 如何判断紧急的程度 priority of interrupt

at the end of F-E cycle, checking if there is an interrupt signal .

• checking the priority of process , if high enough
• saving the register and process states into stack .
• loading the address of ISR （interrupt service routine） into PC,
• once the ISR is completed, resume the interrupted process and run it continually

RTN register transfer notation

MAR <--- [PC]  //the content of PC  is copied into MAR  by  address bus 
MDR <---- [[MAR]] //the content of conent  MAR   is copied into MDR  
CIR <---- [MDR] //the content of MDR  is copied into  CIR  
PC <-- [PC] + 1 //the content of PC  increments 

ACC accumulator 累加器

• contained in ALU
• to store result during calculation temporarily

IX index register

• using indexed addressing
• e.g. finding the address of a [2 ]

SR state register

• showing the state of result after calcualtion
• contain 4 flags : zero , negative, overflow, carry out

Von Neumann architecture (stored program concept)

• CPU , memory , I/O device
• instruction and data are stored into memory
• the instruction can be feteched and executed
• one after another automatically

ALU:

• arithmetic logic unit, do arithmetic operations,
• Do logic operations
• contain ACC register

CU:

• Control Unit
• decoding the instruction and sending control signal

IAS

• immediate access store
• a piece of memory in CPU to store
• data and instruction to be executed temporarily
• Main memory in CPU (Cache)

Bus

• address bus : transfer address unidirectional
• data bus : transfer data bidirectional
• control bus : transfer control signal bidirectional

control signal 控制信号

• read / write signal to memory
• system clock 系统时钟

system clock

• it is an electrical pulse signal to synchronize all the compements
• in computer system and allow them work together
• unit : Hz

two-pass assembler

one pass

• reading one line of code at a time
• allocate the memory for a line of code
• ignoring unnecessary character like extra space , comments
• checking if the opcode is valid according to instruction set
• create / establish symbol table

two-pass

• reading the souce code line by line
• translate the souce code into object code / executable file
• saving or running the object code