module Risc
# An interpreter for the register level. As the register machine is a simple model,
# interpreting it is not so terribly difficult.
#
# There is a certain amount of basic machinery to fetch and execute the next instruction
# (as a cpu would), and then there is a method for each instruction. Eg an instruction SlotToReg
# will be executed by method execute_SlotToReg
#
# The Interpreter (a bit like a cpu) has a state flag, a current instruction and registers
# We collect the stdout (as a hack not to interpret the OS)
#
class Interpreter
# fire events for changed pc and register contents
include Util::Eventable
include Logging
log_level :info
attr_reader :instruction , :clock # current instruction or pc
attr_reader :registers # the registers, 16 (a hash, sym -> contents)
attr_reader :stdout, :state , :flags # somewhat like the lags on a cpu, hash sym => bool (zero .. . )
#start in state :stopped and set registers to unknown
def initialize()
@stdout , @clock , @state = "", 0 , :stopped
@registers = {}
@flags = { :zero => false , :plus => false ,
:minus => false , :overflow => false }
(0...12).each do |reg|
set_register "r#{reg}".to_sym , "r#{reg}:unknown"
end
end
def start( instruction )
initialize
set_state(:running)
set_instruction( instruction )
end
def set_state( state )
old = @state
return if state == old
@state = state
trigger(:state_changed , old , state )
end
def set_instruction( instruction )
raise "set to same instruction #{instruction}:#{instruction.class}" if @instruction == instruction
old = @instruction
@instruction = instruction
trigger(:instruction_changed, old , instruction)
set_state( :exited) unless instruction
end
def get_register( reg )
reg = reg.symbol if reg.is_a? Risc::RiscValue
raise "Not a register #{reg}" unless Risc::RiscValue.look_like_reg(reg)
@registers[reg]
end
def set_register( reg , val )
old = get_register( reg ) # also ensures format
if val.is_a? Fixnum
@flags[:zero] = (val == 0)
@flags[:plus] = (val >= 0)
@flags[:minus] = (val < 0)
log.debug "Set_flags #{val} :#{@flags.inspect}"
else
@flags[:zero] = @flags[:plus] = true
@flags[:minus] = false
end
return if old === val
reg = reg.symbol if reg.is_a? Risc::RiscValue
val = Parfait.object_space.nil_object if val.nil? #because that's what real code has
@registers[reg] = val
trigger(:register_changed, reg , old , val)
end
def tick
return unless @instruction
@clock += 1
name = @instruction.class.name.split("::").last
log.debug "#{@clock.to_s}: #{@instruction.to_s}"
fetch = send "execute_#{name}"
log.debug register_dump
return unless fetch
set_instruction @instruction.next
end
# Label is a noop.
def execute_Label
true
end
# Instruction interpretation starts here
def execute_DynamicJump
method = get_register(@instruction.register)
set_instruction( method.risc_instructions )
end
def execute_Branch
label = @instruction.label
set_instruction label
false
end
def execute_IsZero
@flags[:zero] ? execute_Branch : true
end
def execute_IsNotZero
@flags[:zero] ? true : execute_Branch
end
def execute_IsPlus
@flags[:plus] ? execute_Branch : true
end
def execute_IsMinus
@flags[:minus] ? execute_Branch : true
end
def execute_LoadConstant
to = @instruction.register
value = @instruction.constant
value = value.value if value.is_a?(Mom::Constant)
set_register( to , value )
true
end
alias :execute_LoadData :execute_LoadConstant
def execute_SlotToReg
object = get_register( @instruction.array )
if( @instruction.index.is_a?(Numeric) )
index = @instruction.index
else
index = get_register(@instruction.index)
end
case object
when Symbol
raise "Must convert symbol to word:#{object}" unless( index == 2 )
value = object.to_s.length
when nil
raise "error #{@instruction} retrieves nil"
else
value = object.get_internal_word( index )
end
set_register( @instruction.register , value )
true
end
def execute_RegToSlot
value = get_register( @instruction.register )
object = get_register( @instruction.array )
if( @instruction.index.is_a?(Numeric) )
index = @instruction.index
else
index = get_register(@instruction.index)
end
object.set_internal_word( index , value )
trigger(:object_changed, @instruction.array , index)
true
end
def execute_ByteToReg
object = get_register( @instruction.array )
if( @instruction.index.is_a?(Numeric) )
index = @instruction.index
else
index = get_register(@instruction.index)
end
raise "Unsupported action, must convert symbol to word:#{object}" if object.is_a?(Symbol)
value = object.get_char( index )
#value = value.object_id unless value.is_a? Fixnum
set_register( @instruction.register , value )
true
end
def execute_RegToByte
value = get_register( @instruction.register )
object = get_register( @instruction.array )
if( @instruction.index.is_a?(Numeric) )
index = @instruction.index
else
index = get_register(@instruction.index)
end
object.set_char( index , value )
trigger(:object_changed, @instruction.array , index / 4 )
true
end
def execute_Transfer
value = get_register @instruction.from
set_register @instruction.to , value
true
end
def execute_FunctionCall
set_instruction @instruction.method.risc_instructions
false
end
def execute_FunctionReturn
link = get_register( @instruction.register )
log.debug "Return to #{link}"
@instruction = link
# we jump back to the call instruction. so it is as if the call never happened and we continue
true
end
def execute_Syscall
name = @instruction.name
ret_value = 0
case name
when :putstring
ret_value = handle_putstring
when :exit
set_instruction(nil)
return false
else
raise "un-implemented syscall #{name}"
end
set_register( :r0 , ret_value ) # syscalls return into r0 , usually some int
true
end
def handle_putstring
str = get_register( :r1 ) # should test length, ie r2
case str
when Symbol
@stdout += str.to_s
return str.to_s.length
when Parfait::Word
@stdout += str.to_string
return str.char_length
else
raise "NO string for putstring #{str.class}:#{str.object_id}" unless str.is_a?(Symbol)
end
end
def execute_OperatorInstruction
left = get_register(@instruction.left) || 0
rr = @instruction.right
right = get_register(rr) || 0
@flags[:overflow] = false
result = handle_operator(left,right)
if( result > 2**32 )
@flags[:overflow] = true
result = result % 2**32
else
result = result.to_i
end
log.debug "#{@instruction} == #{result}(#{result.class}) (#{left}|#{right})"
right = set_register(@instruction.left , result)
true
end
def make_op_arg(arg)
case arg
when Integer
arg
when Parfait::Word
arg.to_string.to_sym.object_id
when String
arg.to_sym.object_id
when Symbol
arg.object_id
when Parfait::Object
arg.object_id
else
raise "Op arg #{arg}:#{arg.class}"
end
end
def handle_operator(left, right)
left = make_op_arg(left)
right = make_op_arg(right)
case @instruction.operator
when :+
left + right
when :-
if( left.is_a?(String) or right.is_a?(String))
left == right ? 0 : 1 #for opal, and exception
else
left - right
end
when :>>
left / (2**right)
when :<<
left * (2**right)
when :*
left * right
when :&
left & right
when :|
left | right
else
raise "unimplemented '#{@instruction.operator}' #{@instruction}"
end
end
def register_dump
(0..7).collect do |reg|
value = @registers["r#{reg}".to_sym]
"#{reg}-" +
case value
when String
value[0..10]
else
value.class.name.split("::").last
end
end.join("|")
end
end
end