content: {-|
  Copyright  :  (C) 2015-2016, University of Twente,
                    2017     , Google Inc.
                    2019     , Myrtle Software Ltd,
                    2021-2022, QBayLogic B.V.
  License    :  BSD2 (see the file LICENSE)
  Maintainer :  QBayLogic B.V. <devops@qbaylogic.com>
  
  ROMs
  -}
  
  {-# LANGUAGE BangPatterns #-}
  {-# LANGUAGE CPP #-}
  {-# LANGUAGE GADTs #-}
  {-# LANGUAGE RankNTypes #-}
  
  {-# LANGUAGE Trustworthy #-}
  
  {-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
  {-# OPTIONS_HADDOCK show-extensions #-}
  
  module Clash.Explicit.ROM
    ( -- * Synchronous ROM synchronized to an arbitrary clock
      rom
    , romPow2
      -- * Internal
    , rom#
    )
  where
  
  import Data.Array             (listArray)
  import Data.Array.Base        (unsafeAt)
  import GHC.Stack              (withFrozenCallStack)
  import GHC.TypeLits           (KnownNat, type (^))
  import Prelude hiding         (length)
  
  import Clash.Annotations.Primitive (hasBlackBox)
  import Clash.Signal.Internal
    (Clock (..), KnownDomain, Signal (..), Enable, fromEnable)
  import Clash.Sized.Unsigned   (Unsigned)
  import Clash.Sized.Vector     (Vec, length, toList)
  import Clash.XException       (deepErrorX, seqX, NFDataX)
  
  -- | A ROM with a synchronous read port, with space for 2^@n@ elements
  --
  -- * __NB__: Read value is delayed by 1 cycle
  -- * __NB__: Initial output value is /undefined/, reading it will throw an
  -- 'Clash.XException.XException'
  --
  -- === See also:
  --
  -- * See "Clash.Sized.Fixed#creatingdatafiles" and "Clash.Explicit.BlockRam#usingrams"
  -- for ideas on how to use ROMs and RAMs.
  -- * A large 'Vec' for the content may be too inefficient, depending on how it
  -- is constructed. See 'Clash.Explicit.ROM.File.romFilePow2' and
  -- 'Clash.Explicit.ROM.Blob.romBlobPow2' for different approaches that scale
  -- well.
  romPow2
    :: (KnownDomain dom, KnownNat n, NFDataX a)
    => Clock dom
    -- ^ 'Clock' to synchronize to
    -> Enable dom
    -- ^ 'Enable' line
    -> Vec (2^n) a
    -- ^ ROM content
    --
    -- __NB__: __MUST__ be a constant
    -> Signal dom (Unsigned n)
    -- ^ Read address @r@
    -> Signal dom a
    -- ^ The value of the ROM at address @r@ from the previous clock cycle
  romPow2 = rom
  {-# INLINE romPow2 #-}
  
  -- | A ROM with a synchronous read port, with space for @n@ elements
  --
  -- * __NB__: Read value is delayed by 1 cycle
  -- * __NB__: Initial output value is /undefined/, reading it will throw an
  -- 'Clash.XException.XException'
  --
  -- === See also:
  --
  -- * See "Clash.Sized.Fixed#creatingdatafiles" and "Clash.Explicit.BlockRam#usingrams"
  -- for ideas on how to use ROMs and RAMs.
  -- * A large 'Vec' for the content may be too inefficient, depending on how it
  -- is constructed. See 'Clash.Explicit.ROM.File.romFile' and
  -- 'Clash.Explicit.ROM.Blob.romBlob' for different approaches that scale well.
  rom
    :: (KnownDomain dom, KnownNat n, NFDataX a, Enum addr)
    => Clock dom
    -- ^ 'Clock' to synchronize to
    -> Enable dom
    -- ^ 'Enable' line
    -> Vec n a
    -- ^ ROM content, also determines the size, @n@, of the ROM
    --
    -- __NB__: __MUST__ be a constant
    -> Signal dom addr
    -- ^ Read address @r@
    -> Signal dom a
    -- ^ The value of the ROM at address @r@ from the previous clock cycle
  rom = \clk en content rd -> rom# clk en content (fromEnum <$> rd)
  {-# INLINE rom #-}
  
  -- | ROM primitive
  rom#
    :: forall dom n a
     . (KnownDomain dom, KnownNat n, NFDataX a)
    => Clock dom
    -- ^ 'Clock' to synchronize to
    -> Enable dom
    -- ^ 'Enable' line
    -> Vec n a
    -- ^ ROM content, also determines the size, @n@, of the ROM
    --
    -- __NB__: __MUST__ be a constant
    -> Signal dom Int
    -- ^ Read address @rd@
    -> Signal dom a
    -- ^ The value of the ROM at address @rd@ from the previous clock cycle
  rom# !_ en content =
    go
      (withFrozenCallStack (deepErrorX "rom: initial value undefined"))
      (fromEnable en)
   where
    szI = length content
    arr = listArray (0,szI-1) (toList content)
  
    go o (e :- es) rd@(~(r :- rs)) =
      let o1 = if e then safeAt r else o
      -- See [Note: register strictness annotations]
      in  o `seqX` o :- (rd `seq` go o1 es rs)
  
    safeAt :: Int -> a
    safeAt i =
      if (0 <= i) && (i < szI) then
        unsafeAt arr i
      else
        withFrozenCallStack
          (deepErrorX ("rom: address " ++ show i ++
                       " not in range [0.." ++ show szI ++ ")"))
    {-# INLINE safeAt #-}
  -- See: https://github.com/clash-lang/clash-compiler/pull/2511
  {-# CLASH_OPAQUE rom# #-}
  {-# ANN rom# hasBlackBox #-}
  