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loadMemoryFromFile() should place readmemh() inline for better compatibility

See original GitHub issue

loadMemoryFromFile() creates a separate file and uses a SV bind statement. A simple example:

import chisel3._
import chisel3.util.experimental.loadMemoryFromFile

class Foo(val bits: Int, val size: Int, filename: String) extends Module {
  val io = IO(new Bundle {
    val nia = Input(UInt(bits.W))
    val insn = Output(UInt(32.W))
  })

  val memory = Mem(size, UInt(32.W))
  io.insn := memory(io.nia >> 2);
  loadMemoryFromFile(memory, filename)
}

object FooObj extends App {
  chisel3.Driver.execute(Array[String](), () => new Foo(32, 1024, "insns.hex"))
}

# cat Foo.Foo.memory.v
module BindsTo_0_Foo(
  input         clock,
  input         reset,
  input  [31:0] io_nia,
  output [31:0] io_insn
);

initial begin
  $readmemh("insns.hex", Foo.memory);
end
                      endmodule

bind Foo BindsTo_0_Foo BindsTo_0_Foo_Inst(.*);

Yosys doesn’t like this, and likely there are other tools that don’t either. Is there any reason we don’t just place it inline?

Issue Analytics

State:
Created 4 years ago
Reactions:2
Comments:18 (17 by maintainers)

Top GitHub Comments

1reaction

carlosedpcommented, Mar 9, 2021

@antonblanchard check out https://github.com/chipsalliance/firrtl/pull/2107. I’ve added a new annotation allowing inline readmem in Verilog emiter.

Your sample code would become:

import chisel3._
import chisel3.experimental.{ChiselAnnotation, annotate}
import firrtl.annotations.{MemoryFileInlineAnnotation}


class Foo(val bits: Int, val size: Int, filename: String) extends Module {
  val io = IO(new Bundle {
    val nia = Input(UInt(bits.W))
    val insn = Output(UInt(32.W))
  })

  val memory = Mem(size, UInt(32.W))
  io.insn := memory(io.nia >> 2);
  annotate(new ChiselAnnotation {
    override def toFirrtl = MemoryFileInlineAnnotation(memory.toTarget, filename)
  })
}

object FooObj extends App {
  chisel3.Driver.execute(Array[String](), () => new Foo(32, 1024, "insns.hex"))
}

that would generate the appropriate:

initial begin
  $readmemh("insns.hex", memory);
end

It would allow also configuration for binary files instead of hex, like:

import firrtl.annotations.{MemoryFileInlineAnnotation, MemoryLoadFileType}
...
  annotate(new ChiselAnnotation {
    override def toFirrtl = MemoryFileInlineAnnotation(memory.toTarget, "filename.bin", MemoryLoadFileType.Binary)
  })
...

and output

initial begin
  $readmemb("filename.bin", memory);
end

0reactions

carlosedpcommented, Nov 24, 2021

Opened #2260 to address this.

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