fpgasm - FPGA Assembler opensource

[stacksmith]

Introducing fpgasm - an free, opensource FPGA assembler. With 10 reserved words, you can grasp the syntax in minutes. You can design bare-metal circuits, no Verilog or VHDL.

For years I've been looking for a low-level tool, something like an 'assembler', that would let me manually control placement and wiring, and allow me full access to the FPGA substrate. I could not find it, so I wrote it. For a humorous look at how it came about see
https://www.fpgarelated.com/showarticle/39.php

For a one-page summary, go to
https://github.com/stacksmith/fpgasm/wiki/aaa.-Welcome-to-fpgasm!

I hope this tool will help our community and can't wait to see what you will do with it.

Victor Yurkovsky

 

[sky_123]

How would you use it?
Could you paste a simple example of what syntax you would need to use to
implement (say) a NAND gate?
The examples on the web page only showed wiring from one pin to another, e.g.

//
Top() {
  button Buttons level:LVTTL; //pass on LVTTL to Buttons' level
  led Leds;
  wire button's OUT[0:3] to led's IN[0:3];
}

 

[stacksmith]

How would you use it?
Could you paste a simple example of what syntax you would need to use to
implement (say) a NAND gate? The examples on the web page only showed wiring from one pin to another
...

Very good. Wiring from one pin to another is a very important part of using fpgasm. To use a NAND gate, you would wire it in the same way. For instance, let's connect 2 buttons via a NAND gate to an led:

Top() {
  button Buttons;
  led Led0;
  nand Nand2 loc:xy(10,10); //Note that it has to be placed somewhere
  wire button's OUT[0:1] to nand's IN[0:1];  //nand gate inputs
  wire nand's OUT to led's IN;                    //and output
}

But I suspect your next question would be "But where does Nand2 come from?" There are many modules already defined in the "Spartan3" include file, but not Nand2. I suspect you want to see where the rubber meets the road, so instead of using LutG4 or something like that, let's go all the way down and create a definition of Nand2 using a built-in Spartan3 primitive SLICEL:

Nand2(loc) inputs(IN[2]), outputs(OUT){
  slice SLICEL loc:xy(0,0) cfg:{G:#LUT:D=~(A1*A2) GYMUX:G YUSED:0 };
  wire my IN[0] to his G1;
  wire my IN[1] to his G2;
  wire his Y to my OUT;
}

Here some of you will say "all that work for a 2-input NAND gate? Why would anyone bother?" You are right, but have you seen what "hello world" looks like in assembly language? This is a bit of a contrived example - our Nand2 module could represent two sets any logic equation with 4 inputs, with a mux connecting them, with 2 flip-flops, and carry logic at no extra cost - the fpga cell already has all that circuitry built in...In real life you would pack a bit more of custom logic, at least to fill the F lut...