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chisel3.util.experimental

loadMemoryFromFile

object loadMemoryFromFile

loadMemoryFromFile is an annotation generator that helps with loading a memory from a text file. This relies on Verilator and Verilog's $readmemh or $readmemb. The Treadle backend can also recognize this annotation and load memory at run-time.

This annotation, when the FIRRTL compiler runs, triggers the LoadMemoryTransform. That will add Verilog directives to enable the specified memories to be initialized from files.

Example module

Consider a simple Module containing a memory:

import chisel3._
class UsesMem(memoryDepth: Int, memoryType: Data) extends Module {
  val io = IO(new Bundle {
    val address = Input(UInt(memoryType.getWidth.W))
    val value   = Output(memoryType)
  })
  val memory = Mem(memoryDepth, memoryType)
  io.value := memory(io.address)
}

Above module with annotation

To load this memory from the file /workspace/workdir/mem1.hex.txt just add an import and annotate the memory:

import chisel3._
import chisel3.util.experimental.loadMemoryFromFile   // <<-- new import here
class UsesMem(memoryDepth: Int, memoryType: Data) extends Module {
  val io = IO(new Bundle {
    val address = Input(UInt(memoryType.getWidth.W))
    val value   = Output(memoryType)
  })
  val memory = Mem(memoryDepth, memoryType)
  io.value := memory(io.address)
  loadMemoryFromFile(memory, "/workspace/workdir/mem1.hex.txt")  // <<-- Note the annotation here
}

Example file format

A memory file should consist of ASCII text in either hex or binary format. The following example shows such a file formatted to use hex:

 0
 7
 d
15

A binary file can be similarly constructed.

Source
LoadMemoryTransform.scala
See also

LoadMemoryFromFileSpec.scala in the test suite for additional examples.

Chisel3 Wiki entry on "Loading Memories in Simulation"

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  4. def apply[T <: Data](memory: MemBase[T], fileName: String, hexOrBinary: FileType = MemoryLoadFileType.Hex): Unit

    Annotate a memory such that it can be initialized using a file

    Annotate a memory such that it can be initialized using a file

    memory

    the memory

    hexOrBinary

    whether the file uses a hex or binary number representation

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