BIS: the Better Instruction Set

gistfile1.txt

BIS: the Better Instruction Set

REGISTERS
---------

sixteen 32-bit general-purpose registers, numbered 0-15
one     16-bit status register
four    16-bit arithmetic condition registers, numbered 0-3

INSTRUCTION FORMAT LEGEND
-------------------------

n   immediate
c   condition code
r   condition register
x   operand x
y   operand y
z   operand z


STANDARD INSTRUCTION FORMAT
---------------------------

- has support for conditional instruction
- instructions are four bytes long
- each instruction starts with 0 to
  distinguish them from the compact format.

THREE-OPERAND FORMAT (64)
01oooooo 0rrrcccc 0000zzzz yyyyxxxx
01oooooo 1rrrcccc nnnnnnnn yyyyxxxx

TWO-OPERAND FORMAT (32)
001ooooo 0rrrcccc 00000000 yyyyxxxx
001ooooo 1rrrcccc nnnnnnnn nnnnxxxx

ONE-OPERAND FORMAT (16)
0001oooo 0rrrcccc 00000000 0000xxxx
0001oooo 1rrrcccc nnnnnnnn nnnnnnnn

ZERO-OPERAND FORMAT (8)
00001ooo 0rrrcccc 00000000 00000000


COMPACT INSTRUCTION FORMAT
--------------------------

- instructions are two bytes long
- must be a multiple of two in a row, you
  can't have one just there on its own.
- each two-byte instruction starts with 1.

(to be expanded later)


CONDITIONAL INSTRUCTIONS
------------------------

If the condition register is nonzero then the
instruction is executed iff the corresponding
condition bit is set. 

If the condition register is zero then the
instruction is executed unconditionally.


INSTRUCTION LISTING
-------------------

lbz  load byte and zero-extend
lhs  load half and sign-extend
lhz  load half and zero-extend
lw   load word

THREE-OPERAND FORMAT (64) - instr x,y,z
01 0ooooo Arrrcccc zzzzzzzz yyyyxxxx
01 10oooo Arrrcccc zzzzzzzz yyyyxxxx

01 110000 Arrrcccc nnnnnnnn yyyyxxxx   lbz    x := ZERO_EXTEND_8_TO_32(*(y+n))
01 110001 Arrrcccc nnnnnnnn yyyyxxxx   lbzu   x := ZERO_EXTEND_8_TO_32(*(y+n)); y := y+n
01 110010 Arrrcccc 0000zzzz yyyyxxxx   lbzx   x := ZERO_EXTEND_8_TO_32(*(y+z))
01 110011 Arrrcccc 0000zzzz yyyyxxxx   lbzux  x := ZERO_EXTEND_8_TO_32(*(y+z)); y := y+z
gist
01 1101oo Arrrcccc nnnnnnnn yyyyxxxx   lhs    x := SIGN_EXTEND_16_TO_32(*(y+n))
01 1101oo Arrrcccc nnnnnnnn yyyyxxxx   lhsu   x := SIGN_EXTEND_16_TO_32(*(y+n)); y := y+n
01 1101oo Arrrcccc 0000zzzz yyyyxxxx   lhsx   x := SIGN_EXTEND_16_TO_32(*(y+z))
01 1101oo Arrrcccc 0000zzzz yyyyxxxx   lhsux  x := SIGN_EXTEND_16_TO_32(*(y+z)); y := y+z

01 1110oo Arrrcccc nnnnnnnn yyyyxxxx   lhz    x := ZERO_EXTEND_16_TO_32(*(y+n))
01 1110oo Arrrcccc nnnnnnnn yyyyxxxx   lhzu   x := ZERO_EXTEND_16_TO_32(*(y+n)); y := y+n
01 1110oo Arrrcccc 0000zzzz yyyyxxxx   lhzx   x := ZERO_EXTEND_16_TO_32(*(y+z))
01 1110oo Arrrcccc 0000zzzz yyyyxxxx   lhzux  x := ZERO_EXTEND_16_TO_32(*(y+z)); y := y+z

01 1111oo Arrrcccc nnnnnnnn yyyyxxxx   lw     x := *(y+n)
01 1111oo Arrrcccc nnnnnnnn yyyyxxxx   lwu    x := *(y+n); y := y+n
01 1111oo Arrrcccc 0000zzzz yyyyxxxx   lwx    x := *(y+z)
01 1111oo Arrrcccc 0000zzzz yyyyxxxx   lwux   x := *(y+z); y := y+z

TWO-OPERAND FORMAT (32)
001 00000 Arrrcccc yyyyyyyy yyyyxxxx   mov    x := y
001 00001 Arrrcccc yyyyyyyy yyyyxxxx   swp    x := y; y := x  (in parallel)
001 00010 Arrrcccc yyyyyyyy yyyyxxxx   not    x := !y
001 00011 Arrrcccc yyyyyyyy yyyyxxxx   (reserved)
001 00100 Arrrcccc yyyyyyyy yyyyxxxx   sxtb   x := SIGN_EXTEND_8_TO_32(y)
001 00101 Arrrcccc yyyyyyyy yyyyxxxx   sxtw   x := SIGN_EXTEND_16_TO_32(y)
001 00110 Arrrcccc yyyyyyyy yyyyxxxx   zxtb   x := ZERO_EXTEND_8_TO_32(y)
001 00111 Arrrcccc yyyyyyyy yyyyxxxx   zxtw   x := ZERO_EXTEND_16_TO_32(y)
001 01ooo Arrrcccc yyyyyyyy yyyyxxxx   (reserved)
001 1oooo Arrrcccc yyyyyyyy yyyyxxxx   (reserved)

ONE-OPERAND FORMAT (16)
0001 0000 Arrrcccc xxxxxxxx xxxxxxxx   (reserved)
0001 0001 Arrrcccc xxxxxxxx xxxxxxxx   pop    *(SP++)] := x
0001 0010 Arrrcccc xxxxxxxx xxxxxxxx   push   x := *(--SP)
0001 0011 Arrrcccc xxxxxxxx xxxxxxxx   b      PC := x
0001 0100 Arrrcccc xxxxxxxx xxxxxxxx   call   *(SP++) := PC; PC := x
0001 0101 Arrrcccc xxxxxxxx xxxxxxxx   br     PC += x
0001 0110 Arrrcccc xxxxxxxx xxxxxxxx   callr  *(SP++) := PC; PC += x
0001 0111 Arrrcccc xxxxxxxx xxxxxxxx   int    (software interrupt)
0001 1ooo Arrrcccc xxxxxxxx xxxxxxxx   (reserved)

ZERO-OPERAND FORMAT (8)
00001 000 0rrrcccc 00000000 00000000   ret    PC := *(--SP)
00001 001 0rrrcccc 00000000 00000000   brk    PC := PC
00001 010 0rrrcccc 00000000 00000000   sleep  (sleep until interrupt)
00001 011 0rrrcccc 00000000 00000000   rfi    (return from interrupt)
00001 ooo 0rrrcccc 00000000 00000000   (reserved)


INTERRUPTS
----------

(to be expanded later)