中山大學(xué)軟件工程(移動(dòng)信息工程)專業(yè)課導(dǎo)論課件第七節(jié)

1、Chapter 7Low-Level ProgrammingLanguagesChapter GoalsList the operations that a computer can performDiscuss the relationship between levels of abstraction and the determination of concrete algorithm stepsDescribe the important features of the Pep/7 virtual machineDistinguish between immediate mode ad

2、dressing and direct addressingChapter Goals Convert a simple algorithm into a machine-language programDistinguish between machine language and assembly languageDescribe the steps in creating and running an assembly-language programConvert a simple algorithm into an assembly-language programChapter G

3、oals Distinguish between instructions to the assembler and instructions to be translated Describe two approaches to testingDesign and implement a test plan for a simple assembly-language program Computer Operations A computer is a programmable electronic device that can store, retrieve, and process

4、dataData and instructions to manipulate the data are logically the same and can be stored in the same placeStore, retrieve, and process are actions that the computer can perform on data Machine Language Machine language The instructions built into the hardware of a particular computer Initially, hum

5、ans had no choice but to write programs in machine language because other programming languages had not yet been invented Machine LanguageEvery processor type has its own set of specific machine instructionsThe relationship between the processor and the instructions it can carry out is completely in

6、tegrated Each machine-language instruction does only one very low-level task Pep/7: A Virtual Computer Virtual computer A hypothetical machine designed to contain the important features of real computers that we wantto illustratePep/7designed by Stanley Warfordhas 32 machine-language instructionsWe

7、are only going to examine a fewof these instructionsFeatures in Pep/7The memory unit is made up of 4,096bytes Pep/7 Registers/Status Bits CoveredThe program counter(PC (contains the addressof the next instruction to be executedThe instruction register(IR(contains a copy of the instruction being exec

8、utedThe accumulator(A registerStatus bit N(1if A register is negative;0otherwiseStatus bit Z(1if the A register is0;and0otherwiseFeatures in Pep/7 Figure 7.1Pep/7s architectureInstruction FormatThere are two parts to an instruction The 8-bit instruction specifierAnd optionally, the 16-bit operand sp

9、ecifier Instruction Format The instruction specifier is made up ofseveral sectionsThe operation codeThe register specifierThe addressing-mode specifier Instruction FormatThe operation code specifies which instruction is to be carried outThe 1-bit register specifier is 0 if register A (the accumulato

10、r is involved, which is the case in this chapter.The 2-bit addressing-mode specifier says how to interpret the operand part of the instructionInstruction Format Some Sample Instructions Figure 7.3 Subset of Pep/7 instructionsA Program Example Lets write "Hello" on the screen Pep/7 Simulato

11、r A program that behaves just like the Pep/7 virtual machine behavesTo run a program, we enter the hexadecimal code, byte by byte with blanks between each Assembly Language Assembly languages A language thatuses mnemonic codes to representmachine-language instructionsThe programmer uses these alphan

12、umeric codes in place of binary digitsA program called an assembler reads each of the instructions in mnemonic form andtranslates it into the machine-languageequivalentPep/7 Assembly Language Figure 7.5Assembly Process A New Program 7-21 Our Completed Program 7-22 Status Bits Status bits allow a pro

13、gram to make a choice. BRLT Set the PC to the operand, if N is 1 (A register is less than zero BREQ Set the PC to operand, if Z is 1 (A register is equal to zero 7-23 Testing Test plan A document that specifies how many times and with what data the program must be run in order to thoroughly test the program A cod