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99 lines
3.0 KiB
Markdown
99 lines
3.0 KiB
Markdown
---
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title: "05-6809-assembly"
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aliases:
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tags:
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- lecture
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- cosc204
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---
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# Warnings
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- different CPU architectures have their own machine codes and their own assembly languages
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- assembly language programs are **not** portable across CPU architectures (e.g., 6809 to x86 ARM) but are often backwards compatible (e.g., x86_64 family)
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# Working up
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- High level languages
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- ↓ Compiler ↓
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- Assembly language
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- ↓ Assembler ↓
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- Machine code
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- ↓ Instruction Set ↓
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- Hardware
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# Motorola MC6809 CPU
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- 6809 (1978) 9000 transistors
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- Apple M1 Ultra (2022) 114,000,000,000 transistors
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# Machine Code
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- Computers are controlled by bit-patterns.
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- These patterns determine what the CPU does and to which memory location
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- Assign values to registers
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- load registers from memory
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- add numbers to registers
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- store registers in memory
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- and so on
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- This is called machine code
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It is not very easy to programm this way
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- slow
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- not human readable
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- difficult to debug
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- etc
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To make the process easier, we assign names to the numbers. This allows us to program symbolically. We call this assembly language programming
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## Programmer's Model
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The programmer's model of a computer is not the same as the hardware model. The hardware makes the computer look a particular way to the programmer
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- e.g., your computer could have several memory chips in it, but it looks like one continuous block of memory
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## 6809 Memory
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- 64KB memory
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- called *memory space* or *address space*
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- each byte in numbered from $0000 to $FFFF
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- $ means hex (base 16)
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- for our purposes, all memory locations exist
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- so the computer memory is just an array
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- `unsigned char memory[65536]`
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- the 6809 memory is conceptually broken into **pages** of 256 bytes each
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- the first page is called zero page ( all address are of the form $00xx)
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- the second page is called page 1 ($01xx)
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- and so on
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## 6809 Registers
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- Registers are like global variables
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- some are general purpose (X, Y)
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- some are broken down like a `struct` or `union`
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- D is made u of A and B
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- Write to A or B and D changes
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- Write a 16 bit value to D
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- Read each byte usinig A or B
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- some have special meaning
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- DP - direct page register, can beused to make instuctons that refer to the same memory page faster
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- PC - the program counter, stores the location of the instruction that is currently being executed
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- S - system stack pointer is just an index
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## 6502 Fibonacci in Machine Code
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Example program:
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- 4C 13 00 00 00 00 00 00
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- 00 00 00 00 00 00 00 00
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- 00 00 00 A2 10 A9 01 8D
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- 10 00 8D 11 00 8D 12 00
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- A9 31 8D 0F 00 8D 0F 00
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- AD 10 00 6D 11 00 8D 12
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- 00 69 30 8D 0F 00 AD 11
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- 00 8D 10 00 AD 12 00 8D
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- 11 00 CA D0 E3
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[visualisation of comuter](http://www.visual6502.org/JSSim/expert.html?loglevel=0&a=0000&d=4C130000000000000000000000000000000000A210A9018D10008D11008D1200A9318D0F008D0F00AD10006D11008D120069308D0F00AD11008D1000AD12008D1100CAD0E3)
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