Clash.Prelude.BlockRam.Blob

Efficient bundling of initial RAM content with the compiled code

Leveraging Template Haskell, the initial content for the blockRAM components in this module is stored alongside the compiled Haskell code. It covers use cases where passing the initial content as a Vec turns out to be problematically slow.

The data is stored efficiently, with very little overhead (worst-case 7%, often no overhead at all).

Unlike Clash.Prelude.BlockRam.File, Clash.Prelude.BlockRam.Blob generates practically the same HDL as Clash.Prelude.BlockRam and is compatible with all tools consuming the generated HDL.

BlockRAMs initialized with a MemBlob

blockRamBlob

Arguments

:: forall dom addr m n. (HiddenClock dom, HiddenEnable dom, Enum addr)

=> MemBlob n m

Initial content of the RAM, also determines the size, n, of the RAM

NB: MUST be a constant

-> Signal dom addr

Read address r

-> Signal dom (Maybe (addr, BitVector m))

(write address w, value to write)

-> Signal dom (BitVector m)

Value of the blockRAM at address r from the previous clock cycle

Create a blockRAM with space for n elements

• NB: Read value is delayed by 1 cycle
• NB: Initial output value is undefined, reading it will throw an XException

Additional helpful information:

• See Clash.Prelude.BlockRam for more information on how to use a Block RAM.
• Use the adapter readNew for obtaining write-before-read semantics like this: readNew (blockRamBlob content) rd wrM.

blockRamBlobPow2

Arguments

:: forall dom m n. (HiddenClock dom, HiddenEnable dom, KnownNat n)

=> MemBlob (2 ^ n) m

Initial content of the RAM, also determines the size, 2^n, of the RAM

NB: MUST be a constant

-> Signal dom (Unsigned n)

Read address r

-> Signal dom (Maybe (Unsigned n, BitVector m))

(write address w, value to write)

-> Signal dom (BitVector m)

Value of the blockRAM at address r from the previous clock cycle

Create a blockRAM 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 XException

Additional helpful information:

• See Clash.Prelude.BlockRam for more information on how to use a Block RAM.
• Use the adapter readNew for obtaining write-before-read semantics like this: readNew (blockRamBlobPow2 content) rd wrM.

Creating and inspecting MemBlob

data MemBlob (n :: Nat) (m :: Nat)

Efficient storage of memory content

It holds n words of BitVector m.

Instances

Show (MemBlob n m)

Defined in Clash.Explicit.BlockRam.Internal

Methods

showsPrec :: Int -> MemBlob n m -> ShowS

show :: MemBlob n m -> String

showList :: [MemBlob n m] -> ShowS

createMemBlob

Arguments

:: forall a f. (Foldable f, BitPack a)

=> String

Name of the binding to generate

-> Maybe Bit

Value to map don't care bits to. Nothing means throwing an error on don't care bits.

-> f a

The content for the MemBlob

-> DecsQ

Create a MemBlob binding from a list of values

Since this uses Template Haskell, nothing in the arguments given to createMemBlob can refer to something defined in the same module.

Example

createMemBlob "content" Nothing [15 :: Unsigned 8 .. 17]

ram clk en = blockRamBlob clk en content

The Maybe datatype has don't care bits, where the actual value does not matter. But the bits need a defined value in the memory. Either 0 or 1 can be used, and both are valid representations of the data.

>>> import qualified Prelude as P
>>> let es = [ Nothing, Just (7 :: Unsigned 8), Just 8 ]
>>> :{
createMemBlob "content0" (Just 0) es
createMemBlob "content1" (Just 1) es
x = 1
:}

>>> let pr = mapM_ (putStrLn . show)
>>> pr $ P.map pack es
0b0_...._....
0b1_0000_0111
0b1_0000_1000
>>> pr $ unpackMemBlob content0
0b0_0000_0000
0b1_0000_0111
0b1_0000_1000
>>> pr $ unpackMemBlob content1
0b0_1111_1111
0b1_0000_0111
0b1_0000_1000
>>> :{
createMemBlob "contentN" Nothing es
x = 1
:}

<interactive>:...: error:
    packBVs: cannot convert don't care values. Please specify a mapping to a definite value.

Note how we hinted to clashi that our multi-line command was a list of declarations by including a dummy declaration x = 1. Without this trick, clashi would expect an expression and the Template Haskell would not work.

memBlobTH

Arguments

:: forall a f. (Foldable f, BitPack a)

=> Maybe Bit

Value to map don't care bits to. Nothing means throwing an error on don't care bits.

-> f a

The content for the MemBlob

-> ExpQ

Create a MemBlob from a list of values

Since this uses Template Haskell, nothing in the arguments given to memBlobTH can refer to something defined in the same module.

Example

ram clk en = blockRamBlob clk en $(memBlobTH Nothing [15 :: Unsigned 8 .. 17])

The Maybe datatype has don't care bits, where the actual value does not matter. But the bits need a defined value in the memory. Either 0 or 1 can be used, and both are valid representations of the data.

>>> import qualified Prelude as P
>>> let es = [ Nothing, Just (7 :: Unsigned 8), Just 8 ]
>>> content0 = $(memBlobTH (Just 0) es)
>>> content1 = $(memBlobTH (Just 1) es)
>>> let pr = mapM_ (putStrLn . show)
>>> pr $ P.map pack es
0b0_...._....
0b1_0000_0111
0b1_0000_1000
>>> pr $ unpackMemBlob content0
0b0_0000_0000
0b1_0000_0111
0b1_0000_1000
>>> pr $ unpackMemBlob content1
0b0_1111_1111
0b1_0000_0111
0b1_0000_1000
>>> $(memBlobTH Nothing es)

<interactive>:...: error:
    • packBVs: cannot convert don't care values. Please specify a mapping to a definite value.
    • In the untyped splice: $(memBlobTH Nothing es)

unpackMemBlob :: forall n m. MemBlob n m -> [BitVector m]

Convert a MemBlob back to a list

NB: Not synthesizable