85 lines
2.5 KiB
Markdown
85 lines
2.5 KiB
Markdown
# Paper computer simulator experiment
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## TODO
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- [ ] Document current state of affairs (how to run it etc)
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Computer:
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- [ ] Implement carry flag on SUB
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- [ ] Move screen memory down,
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and add a pointer to screen mem at $00
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to make the screen relocatable
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Misc:
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- [ ] Write some more complex test programs
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- [ ] Display (hex) numbers
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- [ ] Do a proper binary version... (or lose the typed arrays?)
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- [ ] Extract debugging to its own module
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## Instruction set
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0 END
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1 STO lit# ; store ... mem[lit#] <- A
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2 STO addr ; store ... mem[mem[addr]] <- A
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3 LDA lit# ; load ... A <- lit#
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4 LDA addr ; load ... A <- mem[addr]
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5 ADD lit# ; add ... A <- A + lit# ... and un/set carry flag
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6 ADD addr ; add ... A <- A + mem[addr] ... and un/set carry flag
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7 SUB lit# ; sub ... A <- A - lit# ... and un/set carry flag
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8 SUB addr ; sub ... A <- A - mem[addr] ... and un/set carry flag
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9 HOP lit# ; hop ... skip next instruction if A == lit# ... when true: IP <- PC + 2
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A HOP addr ; hop ... skip next instruction if A == addr ... when true: IP <- PC + 2
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B JMP lit# ; jump ... IP <- lit#
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C JMP addr ; jump ... IP <- addr
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D CCF ———— ; clear Carry Flag ... CF = 0
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E CHP ———— ; carry hop ... skip next instruction if Carry Flag is set ... when true: IP <- PC + 2
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F
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- instructions are two bytes long:
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one byte for the opcode, one for the argument
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### Nice features that didn't fit
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- hop `IF<` and hop `IF>`
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- `MUL` and `DIV`
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- rotates and shifts
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## Registers and Flags
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- `A` - accumulator
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- `IP` - instruction pointer (aka program counter)
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- `CF` - carry flag
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## Memory map / Peripherals
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- `00-0F` - 4x4 display
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- `10-1F` - keypad? (details TBD)
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- `20 ` - initial value for IP
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- `20-FF` - free
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### Maybe someday
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- timer (for a version in software/electronic-hardware)
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## Assembly language
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ADD $01 ; comments follow a `;`
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ADD $FF ; this is direct addressing
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ADD ($CC) ; this is indirect addressing
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END ; END, CFC, and CHP don't require arguments
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; (a default value of 0 will be used as their operand)
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@subroutine ; create a label
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ADD $01 ; (it must be on the line before the code it names)
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ADD $02
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JMP @subroutine ; use a label as an argument
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; the label will be replaced with
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; the address of the label
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- Hexadecimal numbers are preceded by a `$`
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- Whitespace is ignored |