CPU-proj/spec.txt

instruction format:
  big endian
  16bits

Bit order:
0 : Largest (leftmost), 7 : smallest (rightmost)


registers:
  r0-r12 (mov 0x0-0xc):
    general purpose
    8 bits
  r13-r15 (mov 0xd-0xf):
    Interrupt reserved
    8 bits
  ac,pr (special 0x0,1):
    accumulator, progam counter
    16bits
  ac0-1,pc0-1 (lds/sts 0x0-1,0x2-3):
    accumulator, progam counter
    8-8bits (lower-upper)
  id (special 0x2):
    interrupt data,
    set by the interrupt
    if raised by bus
    8bits
  in (Special 0x3):
    interrupt register,
    contains the type of
    interrupt
    4bits - bits 0-3 will always be 0
  t bit:
    is set by comp ops
    1bit
calling conventions:
  r0-r1 : return registers
  r2-r11: call args
  r12 : stack pos
  r13-15:interrupt reserved (only adressable in interrupt mode)
  caller pushes desired return addr
  to stack, callee jumps to it
  
Interrupts:
  Hardware interrupts:
    0x0 : Invalid instruction
  The 15 other interrupts are free to
  define by the user
  On interrupt (either called through
  the bus or itp)
startup:
  the cpu will look
  at adress 0x0,and
  expects to find :
    -0x0-1: adress of
     the starting
     point,will be
     jumped to
    -0x2-3: adress of
     the stack, the 
     adress will be
     read here 
     everytime
    -0x4-5:adress of
     the interrupt
     handler, the 
     adress will be
     read here 
     everytime
  When an interrupt is raised, the cpu will allow acces
  to r12-15 and push the resume adress to stack (in
  order pc0 then pc1)
 
instructions :
  format:
    rm,rn: general purpose registers
    #imm:immediate signed 8bit value
    *rm:memory at adress (pc+rm)
    *#imm:memory at adress (pc+#imm)
    sr: pr,ac
    sr0-1: pr0-1/ac0-1, in/id
    st: stack adress that is at 0x2,
     abreviation for explanation only
  nop :
    0b0000000000000000
    0x0000
    No-OP:
    Does nothing
    1 clock
  mov rm,rn:
    0b00100000mmmmnnnn
    0x20mn
    MOVe :
    rm <- rn
    1 clock
  mov rn,#imm:
    0b1000nnnnmmmmmmmm
    0x8nmm
    rn <- #imm
    1 clock
  mov rm,*rn:
    0b11000000mmmmnnnn
    0xB0mn
    rm <- *(pc+rn)
    1 clock
  mov rn,*#imm:
    0b1001nnnnmmmmmmmm
    0x9nmm
    rn <- *(pc+#imm)
    1 clock
  mov *rm,rn:
    0b11000001mmmmnnnn
    0xB1mn
    *(pc+rm) <- rn
    1 clock
  mov *#imm,rn:
    0b1010nnnnmmmmmmmm
    0xAnmm
    *(pc+#imm) <- rn
    1 clock
  mov *rm,*rn:
    0b11000010mmmmnnnn
    0xB2mn
    *(pc+rm) <- *(pc+rn)
    1 clock
  mmv rm, *sr:
    0b11000011mmmmssss
    0xB3ms
    Memory MoVe
    rm <- *sr
    Meant to be used with the accumulator
    1 clock
  mmv *sr, rm:
    0b11000100ssssmmmm
    0xB4sm
    *sr <- rm
    Meant to be used with the accumulator
    1 clock
  psh rm:
    0b11000101mmmm0000
    0xB5m0
    PuSH to stack:
    *(st+r11) <- rm
    r11 <- r11+1
    2 clocks
  pop rm:
    0b11000110mmmm0000
    0xB6m0
    POP from stack
    r11 <- r11-1
    rm <- *(st+r11)
    2 clocks
  lds sr0-1,rm:
    0b11100000ssssmmmm
    0xE0sm
    LoaD Special :
    sr0-1 <- rm
    nop on pc
    1 clock
  sts rm,sr0-1:
    0b11100001mmmmssss
    0xE1ms
    STore Special :
    rm <- sr0-1
    1 clock
  add rn,rm:
    0b01000000nnnnmmmm
    0x40nm
    ADD :
    rn <- rn+rm
    1 clock
  add r0,#imm:
    0b01001000mmmmmmmm
    0x48mm
    r0 <- r0+#imm
    1 clock
  sad sr0-1,rm:
    0b11100010ssssmmmm
    0xE2sm
    Special ADd
    sr0-1 <- sr0-1+rm
    (16bit add)
    nop on pc
    1 clock
  sub rm,rn:
    0b01000001mmmmnnnn
    0x41mn
    SUBstract :
    rm <- rm-rn
    1 clock
  shl rm:
    0b01000010mmmm0000
    0x42m0
    SHift Left
    rm <- rm<<1
    pure shift, no keep sign
    1 clock
  shr rm:
    0b01000011mmmm0000
    0x43m0
    SHift Right
    rm <- rm>>1
    pure shift, no keep sign
    1 clock
  and rm,rn:
    0b01000100mmmmnnnn
    0x44mn
    binary AND :
    rm <- rm&rn
    1 clock
  or rm,rn:
    0b01000101mmmmnnnn
    0x45mn
    binary OR :
    rm <- rm|rn
    1 clock
  xor rm,rn:
    0b01000110mmmmnnnn
    0x46mn
    binary eXclusive OR:
    rm <- rm^rn
    1 clock
  not rm:
    0b01000111mmmmnnnn
    0x47mn
    binary NOT :
    rm <- !rm
    binary not
    1 clock
  rtb :
    0b0110000000000000
    0x6000
    Reset T Bit :
    t <- 0
    1 clock
  gth rm,rn:
    0b01100001mmmmnnnn
    0x61mn
    Greater THan :
    t <- rm > rn ? 1:0
    1 clock
  gts rm,rn:
    0b01100100mmmmnnn
    0x64mn
    Greater Than (Signed):
    t    <- rm     > rn     ? 1:0
            (signed) (signed)
    1 clock
  eql rm,rn:
    0b01100010mmmmnnnn
    0x62mn
    EQuaL :
    t <- rm == rn ? 1:0
    1 clock
  stb rm:
    0b01100011mmmm0000
    0x63m0
    Store T Bit:
    rm <- t
    1 clock
  br *rm:
    0b10110010mmmm0000
    0x32m0
    BRanch :
    pc <- pc + rm     *2
               (signed)
    1 clock
  br *#imm:
    0b10110000mmmmmmmm
    0x30mm
    pc <- pc + #imm*2
    1 clock
  bt *rm:
    0b10110101mmmm0000
    0x35m0
    Branch if True:
    If t == 1,
      pc <- pc + rm     *2
                 (signed)
    else is nop
    1 clock
  bt *#imm:
    0b10110001mmmmmmmm
    0x31mm
    If t == 1,
      pc <- pc + #imm*2
    else is nop
    1 clock
  bf *rm:
    0b10110011mmmm0000
    0x33m0
    Branch if False:
    If t == 0,
      pc <- pc + rm     *2
                 (signed)
    else is nop
    1 clock
  jmp *sr:
    0b10110100ssss0000
    0x34s0
    JuMP :
    pc <- sr
    nop on pc
    2 clocks
  itp rm:
    0b01110001mmmm0000
    0x71m0
    InTerruPt :
    Raises interrupt of id
    rm
    6 clocks
  dsi :
    0b0111001000000000
    0x7200
    DiSable Interrupts:
    Disables interrupts
    1 clock
  eni :
    0b0111001100000000
    0x7300
    ENable Interrupts:
    Enables interrupts
    1 clock
  rgi rm:
    0b01110000mmmm0000
    0x70m0
    ReGister Interrupt :
    rm should be as follows:
      bit 0 : raisable by itp
      bit 1 : raisable by bus
    Sets rm to id on succes,
    and 0xFF on failure
    2 clocks