Clash.Prelude.BlockRam.File

Initializing a block RAM with a data file

Block RAM primitives that can be initialized with a data file. The BNF grammar for this data file is simple:

FILE = LINE+
LINE = BIT+
BIT  = '0'
     | '1'

Consecutive LINEs correspond to consecutive memory addresses starting at 0. For example, a data file memory.bin containing the 9-bit unsigned numbers 7 to 13 looks like:

000000111
000001000
000001001
000001010
000001011
000001100
000001101

Such a file can be produced with memFile:

writeFile "memory.bin" (memFile Nothing [7 :: Unsigned 9 .. 13])

We can instantiate a block RAM using the contents of the file above like so:

f :: (HiddenClock dom, HiddenEnable dom)
  => Signal dom (Unsigned 3)
  -> Signal dom (Unsigned 9)
f rd = unpack <$> blockRamFile d7 "memory.bin" rd (pure Nothing)

In the example above, we basically treat the block RAM as a synchronous ROM. We can see that it works as expected:

>>> import qualified Data.List as L
>>> L.tail $ sampleN 4 $ f (fromList [3..5])
[10,11,12]

However, we can also interpret the same data as a tuple of a 6-bit unsigned number, and a 3-bit signed number:

g :: (HiddenClock dom, HiddenEnable dom)
   => Signal dom (Unsigned 3)
   -> Signal dom (Unsigned 6,Signed 3)
g clk rd = unpack <$> blockRamFile d7 "memory.bin" rd (pure Nothing)

And then we would see:

>>> import qualified Data.List as L
>>> L.tail $ sampleN 4 $ g (fromList [3..5])
[(1,2),(1,3)(1,-4)]

Block RAM synchronized to an arbitrary clock

blockRamFile

Arguments

:: (KnownNat m, Enum addr, NFDataX addr, HiddenClock dom, HiddenEnable dom, HasCallStack)

=> SNat n

Size of the BRAM

-> FilePath

File describing the initial content of the BRAM

-> 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 BRAM at address r from the previous clock cycle

Create a block RAM 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
• NB: This function might not work for specific combinations of code-generation backends and hardware targets. Please check the support table below:

	VHDL	Verilog	SystemVerilog
Altera/Quartus	Broken	Works	Works
Xilinx/ISE	Works	Works	Works
ASIC	Untested	Untested	Untested

See also:

• 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 (blockRamFile size file) rd wrM.
• See Clash.Prelude.BlockRam.File for more information on how to instantiate a block RAM with the contents of a data file.
• See Clash.Sized.Fixed for ideas on how to create your own data files.

blockRamFilePow2

Arguments

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

=> FilePath

File describing the initial content of the BRAM

-> 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 BRAM at address r from the previous clock cycle

Create a block RAM 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
• NB: This function might not work for specific combinations of code-generation backends and hardware targets. Please check the support table below:

	VHDL	Verilog	SystemVerilog
Altera/Quartus	Broken	Works	Works
Xilinx/ISE	Works	Works	Works
ASIC	Untested	Untested	Untested

See also:

• 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 (blockRamFilePow2 file) rd wrM.
• See Clash.Prelude.BlockRam.File for more information on how to instantiate a block RAM with the contents of a data file.
• See Clash.Sized.Fixed for ideas on how to create your own data files.

Producing files

memFile

Arguments

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

=> Maybe Bit

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

-> f a

Values to convert

-> String

Contents of the memory file

Convert data to the String contents of a memory file.

• NB: Not synthesizable

• The following document the several ways to instantiate components with files:

  • Clash.Prelude.BlockRam.File
  • Clash.Prelude.ROM.File
  • Clash.Explicit.BlockRam.File
  • Clash.Explicit.ROM.File
• See Clash.Sized.Fixed for more ideas on how to create your own data files.

Example

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.

>>> let es = [ Nothing, Just (7 :: Unsigned 8), Just 8]
>>> mapM_ (putStrLn . show . pack) es
0b0_...._....
0b1_0000_0111
0b1_0000_1000
>>> putStr (memFile (Just 0) es)
000000000
100000111
100001000
>>> putStr (memFile (Just 1) es)
011111111
100000111
100001000