Clash.Prelude.Mealy

Whereas the output of a Moore machine depends on the previous state, the output of a Mealy machine depends on current transition.

Mealy machines are strictly more expressive, but may impose stricter timing requirements.

Mealy machine synchronised to the system clock

mealy

Arguments

:: HiddenClockReset domain gated synchronous

=> (s -> i -> (s, o))

Transfer function in mealy machine form: state -> input -> (newstate,output)

-> s

Initial state

-> Signal domain i -> Signal domain o

Synchronous sequential function with input and output matching that of the mealy machine

Create a synchronous function from a combinational function describing a mealy machine

macT
  :: Int        -- Current state
  -> (Int,Int)  -- Input
  -> (Int,Int)  -- (Updated state, output)
macT s (x,y) = (s',s)
  where
    s' = x * y + s

mac :: HiddenClockReset domain gated synchronous => Signal domain (Int, Int) -> Signal domain Int
mac = mealy macT 0

>>> simulate mac [(1,1),(2,2),(3,3),(4,4)]
[0,1,5,14...
...

Synchronous sequential functions can be composed just like their combinational counterpart:

dualMac
  :: HiddenClockReset domain gated synchronous
  => (Signal domain Int, Signal domain Int)
  -> (Signal domain Int, Signal domain Int)
  -> Signal domain Int
dualMac (a,b) (x,y) = s1 + s2
  where
    s1 = mealy mac 0 (bundle (a,x))
    s2 = mealy mac 0 (bundle (b,y))

mealyB

Arguments

:: (Bundle i, Bundle o, HiddenClockReset domain gated synchronous)

=> (s -> i -> (s, o))

Transfer function in mealy machine form: state -> input -> (newstate,output)

-> s

Initial state

-> Unbundled domain i -> Unbundled domain o

Synchronous sequential function with input and output matching that of the mealy machine

A version of mealy that does automatic Bundleing

Given a function f of type:

f :: Int -> (Bool, Int) -> (Int, (Int, Bool))

When we want to make compositions of f in g using mealy, we have to write:

g a b c = (b1,b2,i2)
  where
    (i1,b1) = unbundle (mealy f 0 (bundle (a,b)))
    (i2,b2) = unbundle (mealy f 3 (bundle (i1,c)))

Using mealyB however we can write:

g a b c = (b1,b2,i2)
  where
    (i1,b1) = mealyB f 0 (a,b)
    (i2,b2) = mealyB f 3 (i1,c)

(<^>)

Arguments

:: (Bundle i, Bundle o, HiddenClockReset domain gated synchronous)

=> (s -> i -> (s, o))

Transfer function in mealy machine form: state -> input -> (newstate,output)

-> s

Initial state

-> Unbundled domain i -> Unbundled domain o

Synchronous sequential function with input and output matching that of the mealy machine

Infix version of mealyB