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Chapter 7 - Assembly language. The main contents of this chapter include all of the following: Assembly language programming - Moving up a level, an assembly language program, the assembly process, beyond the assembly of a single assembly language program. | Chapter 7 Assembly Language Human-Readable Machine Language Computers like ones and zeros Humans like symbols Assembler is a program that turns symbols into machine instructions. ISA-specific: close correspondence between symbols and instruction set mnemonics for opcodes labels for memory locations additional operations for allocating storage and initializing data ADD R6,R2,R6 ; increment index reg. 0001110010000110 7- An Assembly Language Program ; ; Program to multiply a number by the constant 6 ; .ORIG x3050 LD R1, SIX LD R2, NUMBER AND R3, R3, #0 ; Clear R3. It will ; contain the product. ; The inner loop ; AGAIN ADD R3, R3, R2 ADD R1, R1, #-1 ; R1 keeps track of BRp AGAIN ; the iteration. ; HALT ; NUMBER .BLKW 1 SIX .FILL x0006 ; .END 7- LC-2 Assembly Language Syntax Each line of a program is one of the following: an instruction an assember directive (or pseudo-op) a comment Whitespace (between symbols) and case are ignored. Comments (beginning with “;”) are also ignored. An instruction has the following format: LABEL OPCODE OPERANDS COMMENTS optional mandatory 7- Opcodes and Operands Opcodes reserved symbols that correspond to LC-2 instructions listed in Appendix A ex: ADD, AND, LD, LDR, Operands registers -- specified by Rn, where n is the register number numbers -- indicated by # (decimal) or x (hex) label -- symbolic name of memory location separated by comma number, order, and type correspond to instruction format ex: ADD R1,R1,R3 ADD R1,R1,#3 LD R6,NUMBER BRz LOOP 7- Labels and Comments Label placed at the beginning of the line assigns a symbolic name to the address corresponding to line ex: LOOP ADD R1,R1,#-1 BRp LOOP Comment anything after a semicolon is a comment ignored by assembler used by humans to document/understand programs tips for useful comments: avoid restating the obvious, as “decrement R1” provide additional insight, as in “accumulate product in R6” use comments to separate pieces of program 7- Assembler . | Chapter 7 Assembly Language Human-Readable Machine Language Computers like ones and zeros Humans like symbols Assembler is a program that turns symbols into machine instructions. ISA-specific: close correspondence between symbols and instruction set mnemonics for opcodes labels for memory locations additional operations for allocating storage and initializing data ADD R6,R2,R6 ; increment index reg. 0001110010000110 7- An Assembly Language Program ; ; Program to multiply a number by the constant 6 ; .ORIG x3050 LD R1, SIX LD R2, NUMBER AND R3, R3, #0 ; Clear R3. It will ; contain the product. ; The inner loop ; AGAIN ADD R3, R3, R2 ADD R1, R1, #-1 ; R1 keeps track of BRp AGAIN ; the iteration. ; HALT ; NUMBER .BLKW 1 SIX .FILL x0006 ; .END 7- LC-2 Assembly Language Syntax Each line of a program is one of the following: an instruction an assember directive (or pseudo-op) a comment Whitespace (between symbols) and case are ignored. Comments (beginning with “;”) are also .
