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README.md

TinyComputer++

A C++ implementation of Carlos Sanchez's TinyComputer - a virtual machine based on a custom assembly language.

http://smilebasicsource.com/tinycomputer/

In action

Architecture

  • Numbers: Signed 32 bit
  • Parameters: Signed 16 bit
  • Instruction Width: 64 bit
  • Opcodes: 7 bits
  • Program space: 65536 instructions
  • Little Endian

Memory

There are two memory banks, the RAM and the ROM.

  • RAM: 65536 32 bit values, numbered 0-65535
  • ROM: 65536 32 bit values, numbered 0-65535

RAM can be referenced using the parameter prefixes m and v, meaning memory and video resepctively. By convention, the v prefix is only used when referencing the video area of the RAM. Additionally, RAM can be referenced via pointer using the * prefix.

ROM can be referenced using the parameter prefix b, meaning button (legacy). ROM cannot be referenced via pointer.

Video

Video is implemented as a 32x32 black and white matrix display. The first 32 memory addresses (0-31) are reserved for video memory. These These addresses are bitfields representing the rows of the screen from top to bottom, where the LSB is on the left and the MSB is on the right.

Structure of an instruction

An instruction is 64 bits wide, with the first 16 including the opcode and metadata for the parameters, and the other three sets of 16 bits representing the parameters for the instruction.

For the first 16 bits the 9 most significant bits are metadata triplets, and the 7 least significant bits are the opcode.

PBM PBM PBM 0123456 | 0123456789ABCDEF | 0123456789ABCDEF | 0123456789ABCDEF
Metadata    Opcode  | First Parameter  | Second Parameter | Third Parameter

For the metadata the least significant triplet represents the first parameter. Bit P indicates whether the parameter is a pointer, bit B represents if it is an address in the ROM, and bit M represents if it is an address in the RAM. If both bits B and M are set, B takes precedence. If neither M nor B are set, the parameter is an integer literal.

Instructions

Name Opcode Param Count Param1 Type Param2 Type Param3 Type
add 1 3 RO/RW/Num RO/RW/Num RW
sub 2 3 RO/RW/Num RO/RW/Num RW
mul 3 3 RO/RW/Num RO/RW/Num RW
div 4 3 RO/RW/Num RO/RW/Num RW
mod 5 3 RO/RW/Num RO/RW/Num RW
and 6 3 RO/RW/Num RO/RW/Num RW
or 7 3 RO/RW/Num RO/RW/Num RW
xor 8 3 RO/RW/Num RO/RW/Num RW
rs 9 3 RO/RW/Num RO/RW/Num RW
ls 10 3 RO/RW/Num RO/RW/Num RW
not 11 2 RO/RW/Num RW
beq 12 3 RO/RW/Num RO/RW/Num Label
jmp 13 1 Label
vsync 14 0
jrt 15 1 Label
ret 16 0
bgt 17 3 RO/RW/Num RO/RW/Num Label
bne 18 3 RO/RW/Num RO/RW/Num Label

Types are checked regardless of pointer prefix. If the prefix is specified when it would not make sense (e.g. for a label) that is undefined behavior.

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