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chisel3.util.experimental

loadMemoryFromFileInline

object loadMemoryFromFileInline

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

This annotation, when the FIRRTL compiler runs, triggers the MemoryFileInlineAnnotation that will add Verilog directives inlined to the module enabling the specified memories to be initialized from files. The module supports both hex and bin files by passing the appropriate MemoryLoadFileType.FileType argument with MemoryLoadFileType.Hex or MemoryLoadFileType.Binary. Hex is the default.

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.loadMemoryFromFileInline   // <<-- 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)
  loadMemoryFromFileInline(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. Chisel does not validate the file format or existence. It is supposed to be in a path accessible by the synthesis tool together with the generated Verilog.

Source
LoadMemoryTransform.scala
See also

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 inline using a file

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

    memory

    the memory

    fileName

    the file used for initialization

    hexOrBinary

    whether the file uses a hex or binary number representation

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