86 lines
4.7 KiB
Org Mode
86 lines
4.7 KiB
Org Mode
#+TITLE: Terminology
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#+AUTHOR: Riyyi
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#+LANGUAGE: en
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#+OPTIONS: toc:nil
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GameBoy terminology.
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** Terminology
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*** Hardware [[#references][(1)]][[#references][(2)]]
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| Name | Modern equivalent | Description |
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|-----------------+-------------------+-------------------------------------------|
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| APU | Sound card | Audio Processing Unit |
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| PPU | GPU | Pixel Processing Unit |
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| Bootrom | BIOS | |
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| HRAM (High RAM) | CPU cache | Embedded memory inside the CPU, 127 bytes |
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| WRAM (Work RAM) | RAM | |
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*** Flags
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The half-carry flag ~H~ is set when an arithmetic operation on two numbers
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causes a carry from bit #3 to bit #4 for 8-bit operations or a carry from bit
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#11 to bit #12 for 16-bit operations. For 16-bit operation this indicates the
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lower 4 bits of the *second* byte[[#references][(3)]].
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We start counting from the right as bit *#0*!
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*** Opcode
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| Name | Bits | Sign | Mnemonics | [[https://gbdev.io/gb-opcodes/optables/][1]] | [[https://rgbds.gbdev.io/docs/v0.5.2/gbz80.7/][2]] | [[https://gekkio.fi/files/gb-docs/gbctr.pdf][3]]/[[http://marc.rawer.de/Gameboy/Docs/GBCPUman.pdf][3]] | [[https://gbdev.io/pandocs/CPU_Instruction_Set.html][4]] | Description | Note |
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|-----------+------+----------+-----------+------+-----+------+-----+------------------------------+------------------------|
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| | | | | <r> | <r> | <r> | <r> | | |
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| immediate | 8 | unsigned | i8 | d8 | n8 | n | | Next byte in memory | |
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| immediate | 16 | unsigned | i16 | d16 | n16 | nn | | Next byte in memory | little-endian |
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| register | 8 | unsigned | r8 | | r8 | r | | Any of the registers | |
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| register | 16 | unsigned | r16 | | r16 | rr | | Any of the registers | little-endian |
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| address | 8 | unsigned | a8 | | | (n) | | Address at value | |
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| address | 16 | unsigned | a16 or () | a16 | n16 | (nn) | nn | Address at value | little-endian |
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| immediate | 8 | signed | s8 | r8 | e8 | e | dd | Next byte in memory | used as offset |
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| immediate | 8 | unsigned | io8 | (a8) | n16 | (n) | n | 0xff00 + next byte in memory | write to I/O-port |
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| condition | | | <ZNHC> | | cc | | f | Execute if condition met | |
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| constant | 8 | unsigned | b | | u3 | b | n | Single bit at position 'x' | |
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| constant | 8 | unsigned | vec | | vec | | n | One of RST vectors | absolute fixed address |
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d = data \\
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n = constant
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**** Flag conditions
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Flag conditions, sometimes referred to as ~cc~, are the state the flags need to
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be in to execute the opcode. There are four possible checks[[#references][(4)]][[#references][(5)]]:
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| Code | Meaning | State |
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|------+--------------------------------+-------|
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| Z | Execute if Zero flag is set | 1 |
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| NZ | Execute if Zero flag is unset | 0 |
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| C | Execute if Carry flag is set | 1 |
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| NC | Execute if Carry flag is unset | 0 |
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**** RST vectors
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Absolute fixed address, possible values are[[#references][(4)]]: ~0x00~, ~0x08~, ~0x10~, ~0x18~,
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~0x20~, ~0x28~, ~0x30~, and ~0x38~.
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*** Variables
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| Name | Meaning |
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|--------+------------------------|
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| length | amount of elements |
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| size | amount of bytes |
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|--------+------------------------|
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| lhs | left hand side |
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| rhs | right hand side |
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|--------+------------------------|
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| lsb | least significant byte |
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| msb | most significant byte |
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** References
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1. [[https://gbdev.io/pandocs/Memory_Map.html]["Memory Map"]]. rgbdev.io. Retrieved 22 Aug 2022.
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2. [[https://gbdev.io/pandocs/Specifications.html]["Specifications"]]. rgbdev.io. Retrieved 22 Aug 2022.
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3. [[https://robdor.com/2016/08/10/gameboy-emulator-half-carry-flag/]["A Visual Guide to the Gameboy's Half-Carry Flag"]]. robdor.com. Retrieved 24 Aug 2022.
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4. [[https://rgbds.gbdev.io/docs/v0.5.2/gbz80.7#LEGEND]["gbz80(7) — CPU opcode reference"]]. rgbds.gbdev.io. Retrieved 26 Aug 2022.
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5. [[http://www.devrs.com/gb/files/opcodes.html]["GameBoy Opcode Summary"]]. devrs.com. Retrieved 25 Aug 2022.
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