Clash.Explicit.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 machines with explicit clock and reset ports

mealy

Arguments

:: (KnownDomain dom, NFDataX s)

=> Clock dom

Clock to synchronize to

-> Reset dom

-> Enable dom

Global enable

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

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

-> s

Initial state

-> Signal dom i -> Signal dom 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

import qualified Data.List as L

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

mac
  :: KnownDomain dom
  => Clock dom
  -> Reset dom
  -> Enable dom
  -> Signal dom (Int, Int)
  -> Signal dom Int
mac clk rst en = mealy clk rst en macT 0

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

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

dualMac
  :: KnownDomain dom
  => Clock dom
  -> Reset dom
  -> Enable dom
  -> (Signal dom Int, Signal dom Int)
  -> (Signal dom Int, Signal dom Int)
  -> Signal dom Int
dualMac clk rst en (a,b) (x,y) = s1 + s2
  where
    s1 = mealy clk rst en macT 0 (bundle (a,x))
    s2 = mealy clk rst en macT 0 (bundle (b,y))

mealyB

Arguments

:: (KnownDomain dom, NFDataX s, Bundle i, Bundle o)

=> Clock dom

-> Reset dom

-> Enable dom

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

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

-> s

Initial state

-> Unbundled dom i -> Unbundled dom 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 clk rst en a b c = (b1,b2,i2)
  where
    (i1,b1) = unbundle (mealy clk rst en f 0 (bundle (a,b)))
    (i2,b2) = unbundle (mealy clk rst en f 3 (bundle (c,i1)))

Using mealyB however we can write:

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