Điện, điện tử - Chapter 3: Assembly language programming

Chapter 3 Assembly language programming 3.1 Introduction to Assembly Microcomputer principles and applications High level vs. Assembly High level languages Assembly language • More programmer friendly. • Lower level, closer to ISA. • More ISA independent. • Very ISA-dependent. • Each high-level statement translates to several instructions in the ISA of the computer. • Each instruction specifies a single ISA instruction. • Makes low level programming more user friendly. • More efficient code. 3.1 Introduction to Assembly Microcomputer principles and applications Assembler syntax {label[:]} mnemonic {operand list} {;comment} • Symbols: ⋄ Used as labels, constants, and substitution values and stored in a symbol table. ⋄ A symbol name is a string of up to 200 alphanumeric characters (A-Z, a-z, 0-9, $, and _), cannot contain embedded blanks, is case sensitive. ⋄ The first character cannot be a number. • Labels: ⋄ Labels are symbols. 3.1 Introduction to Assembly Microcomputer principles and applications Assembler syntax {label[:]} mnemonic {operand list} {;comment} • Labels: ⋄ Begined in column 1 and is optionally followed by a colon. ⋄ The value of a label is the current value of the Location Counter (address within program). ⋄ A label on a line by itself is a valid statement. ⋄ Labels used locally within a file must be unique. • Mnemonics: ⋄ Cannot start in column 1. If it does, it is interpreted as a label. 3.1 Introduction to Assembly Microcomputer principles and applications Assembler syntax {label[:]} mnemonic {operand list} {;comment} • Mnemonics: ⋄ Contains one of the following items: Instruction, Assembler directive, Macro directive, Macro invocation. ⋄ A label on a line by itself is a valid statement. ⋄ Labels used locally within a file must be unique. • Operands: ⋄ Contains one or more operands. ⋄ An operand may consist of: symbols, constants, expressions. ⋄ Operands are separated with commas. 3.2 Instruction Cycle Microcomputer principles and applications • Instruction Fetch (Get what you need to do). • Instruction Decode (Understand what you need to do). • First Operand Fetch (Not enough information, get some more). • Second Operand Fetch (Still not enough information, get some more). • Execute (Do it !). • Write back (Write result of the operation). 3.3 Addressing Modes Microcomputer principles and applications Source Addressing Modes • Register. • Indexed. • Symbolic (PC Relative). • Absolute Address. • Indirect Register. • Indirect Auto-increment. • Immediate. 3.3 Addressing Modes Microcomputer principles and applications Destination Addressing Modes • Register. • Symbolic (PC Relative). • Absolute Address. • Indexed. 3.3 Addressing Modes Microcomputer principles and applications 3.3.1 Register Mode Example: mov R5, R6 Explanation: Moves the content or the register R5 into R6 without altering R5. Usefulness Save a register to another 3.3 Addressing Modes Microcomputer principles and applications 3.3.2 Indexed Mode Example mov 4(R5), R6 Explanation • Add 4 to the content of R5 inside the CPU • Fetch the memory address from the forementionned computation • Store the value into R6 Usefulness Access an item in memory (eg. an array) with a constant offset 3.3 Addressing Modes Microcomputer principles and applications 3.3.3 Symbolic Mode Example mov 0x1234, R6 explanation • Add 0x1234 to the PC to generate the address. • Fetch the memory from the address of the forementionned computation • Store the value into R6 Usefulness Access an array of data stored in the program memory. 3.3 Addressing Modes Microcomputer principles and applications 3.3.4 Absolute Mode Example mov &0xDEAD, R6 Explanation • Fetch the memory from the address 0xDEAD. • Store the value into R6. Usefulness Access memory at a known address (eg. Peripheral). 3.3 Addressing Modes Microcomputer principles and applications 3.3.5 Indirect Register Mode Example mov @R8, R6 Explanation • Fetch the memory at the address contained in R8. • Store the value into R6. Usefulness Use a register as a pointer to memory. 3.3 Addressing Modes Microcomputer principles and applications 3.3.6 Indirect Autoincrement Mode Example mov @R8+, R6 Explanation • Fetch the memory at the address contained in R8. • Store the value into R6. • Increment R8. Usefulness • Copy a data to somewhere else in 1 instruction. • Stack Popping. 3.3 Addressing Modes Microcomputer principles and applications 3.3.7 Immediate Mode Example mov #0xBEEF, R6 Explanation Load R6 with 0xBEEF Usefulness Initialize a register with a value