96 lines
2.6 KiB
Org Mode
96 lines
2.6 KiB
Org Mode
* Chip8 Emulator
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** The memory Layout
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The Chip8 has 4095 bytes of memory:
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#+begin_src artist
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+-----------------------+
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| | 0xFFF - End of Memory
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+-----------------------+
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| 0x200/0xFFF |
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| ProgramData |
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+-----------------------+ 0x200 - Start of Chip8 programs
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| 0x00/0x1FF |
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| Reserved for Chip8 |
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+-----------------------+ 0x00 - Start of Chip8 RAM
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#+end_src
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Chip-8 has a stack that is an array of 16 16-bit values, used to store the
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addresses that the Chip8 should return to when returning from a subroutine,
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meaning there can be 16 levels of nested subroutines.
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** Registers
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Chip8 has 16 8-bit data registers, each can hold 1 byte of information.
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| Data Registers |
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| V0 |
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| V1 |
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| V2 |
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| V3 |
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| V4 |
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| V5 |
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| V6 |
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| V7 |
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| V8 |
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| V9 |
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| VA |
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| VB |
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| VC |
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| VD |
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| VE |
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| VF |
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That means that the registers should be implemented as an array with a size of
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16:
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| V0 | V1 | V2 | V3 | V4 | V5 | V6 | V7 | V8 | ... |
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The Chip 8 also has some extra registers:
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- *I* - used to store memory addresses.
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- *PC* - points to the address oft he current instruction being executed. All the
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instructions are 2 bytes in size, so this should be incremented by 2 per
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instruction executed.
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- *SP* - 8-bit stack pointer, points to a location in the stack.
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- *Sound Timer*:
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- Chip8 plays a beep when the sound timer is not zero
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- Decrements at a rate of 70hz
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- When zero no sound is played
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- *Delay Timer*:
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- Chip8 stops executing instructions when the delay timer is greater than
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zero.
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- This is also decremented at a rate of 60hz.
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- When the delay timer is zero, the program execution resumes.
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** The Display
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The size of the display is 64x32 pixels, and it's monocrome. Drawing to the
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display is done with sprites, not pixels. If a sprite overflows the screen, it
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wraps it back to the other side. The sprites can be a maximum of 8 bits of
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width, and up to 15 bytes in length.
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** The Keyboard
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The Chip-8 keyboard has 16 keys: from 0 to F.
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This is how the keyboard looks:
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| 1 | 2 | 3 | C |
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| 4 | 5 | 6 | D |
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| 7 | 8 | 9 | E |
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| A | 0 | B | F |
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** Instruction Set
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The Chip-8 instruction set has 36 different insturctions. These instructions can
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be for mathematical operations, drawing and more.
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