Nexys Video FPGA 01: Hello World with Verilog & Vivado

Nexys Video FPGA 01: Hello World with Verilog & Vivado

This Time to Explore tutorial series provides an introduction to development using FPGAs (Field Programmable Gate Arrays). On a microcontroller or PC you write software to run on an existing CPU. With an FPGA you develop the hardware itself at the logic level. This makes FPGAs uniquely flexible and powerful: especially when dealing with complex or parallel tasks and high-speed I/O such as networking and video. 

However, FPGAs are more than just a faster way to do what you already do; they're a fundamentally different tool that can solve many problems that would otherwise be impractical. Different materials have different properties: metal is not simply shiny plastic it has its own strengths and weaknesses. The same applies to FPGAs and microcontrollers: they can be used for some of the same purposes, but are fundamentally different. It's difficult to convey this in words: you really do need to experiment with FPGAs yourself to appreciate what they can do.

No prior experience of FPGA development is required to follow these tutorials, but basic knowledge of programming concepts is assumed. If you can write a simple program in Python, Ruby, or JavaScript then you shouldn't have any trouble with this course.

Finally, I find working with FPGAs gives me a sense of delight so often lacking in modern software development. There's something deeply satisfying about designing at the hardware level, be it drawing graphics on a screen, producing sound from a speaker, or even implementing your own arcade game from scratch. I hope you find these tutorials useful and have fun experimenting with FPGAs.

NB. This series was originally published for the Digilent Arty.

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Shifting Verilog Values for CORDIC and Division

Shifting Verilog Values for CORDIC and Division

Newton-Raphson division and CORDIC methods only work in a small domain. For example, Newton-Raphson division implementations usually expect the divisor to be in the range 0.5 to 1.0. For a large number of bits this requires many single shifts and comparisons. Instead we can create a priority encoder with casex to determine the most significant bit (MSB) and then apply a single shift as required.

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Fixed Point Numbers in Verilog

Fixed Point Numbers in Verilog

Sometimes you need more precision than integers can provide, but floating point is hard (try reading IEEE 754). You could use a library or IP block, but simple fixed point maths can often get the job done with little effort. Furthermore, most FPGAs have dedicated DSP blocks that make multiplication and addition of integers really fast; we can take advantage of that with a fixed point approach.

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FPGA VGA Graphics in Verilog Part 3

FPGA VGA Graphics in Verilog Part 3

Welcome back to my FPGA graphics tutorial series using the Digilent Arty or Basys3 boards. In part 2 we introduced bitmapped displays and loaded graphics files into memory. In this third part we animate sprites using bitmaps and double buffering: this classic technique is a staple of 2D games. By the end of this tutorial you'll be able to control a sprite using the switches on your FPGA board.

The principle of double buffering is simple: you draw on one buffer while driving the monitor from the other. This gives you an entire frame time (1/60th second) to create your image, whilst avoiding any screen tearing. There are two downsides: you need twice the memory and you increase latency by one frame.

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FPGA VGA Graphics in Verilog Part 2

FPGA VGA Graphics in Verilog Part 2

Welcome back to my FPGA graphics tutorial series using the Digilent Arty or Basys3 boards. In part 1 we created a VGA module and used it to animate squares on screen. In this second part, we introduce bitmapped displays. By the end of this tutorial, you'll be able to load your own image into FPGA memory and display it on your monitor.

Bitmaps
A bitmapped display is backed by a memory array: each pixel corresponds to a location in memory. To create the display we read out the value of the current pixel from its memory location. To set the colour of a pixel, we  modify the contents of its associated memory location. Bitmaps provides two significant benefits: we're free to create sophisticated graphics using whatever technique we like, and the setting of pixel colour is separated from the actual screen drawing process. The big downside of a bitmapped display is we need significant memory to store our pixel data.

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Video Timings: VGA, SVGA, 720P, 1080P

Video Timings: VGA, SVGA, 720P, 1080P

You Need Video Timings

To work with standard monitors and TVs you need to use the correct video timings. This recipe includes the timings for three common modes using analogue VGA, DVI or HDMI: 640x480, 1280x720, and 1920x1080 all at 60 Hz.

Video Signals in Brief
Video signals have two phases: drawing pixels and the blanking interval. The sync signals occur within blanking intervals; separated from pixel drawing by the front porch and back porch. Horizontal sync demarcates a line and vertical sync a screen. The following diagram illustrates the different parts of the display signal for 640x480 at 60Hz; the HD resolutions work in a similar way.

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Block Ram in Verilog with Vivado

Block Ram in Verilog with Vivado

You want to use Block Ram in Verilog with Vivado

There are two types of internal memory available on a typical FPGA:

  • Distributed Ram: made from the FPGA logic (LUTs)
  • Block Ram: dedicated memory blocks within the FPGA; also known as bram

However, persuading Vivado to make use of block ram isn't simple a case of changing a preference. You need to create a Verilog implementation that Vivado can infer as block ram. This recipe looks at inferring block ram on Xilinx 7 Series FPGAs (Spartan-7. Artix-7, Kintex-7, and Virtex-7), but this information should be relevant to other developers too. 

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Initialize Memory in Verilog

Initialize Memory in Verilog

You want to initialize memory from a file using Verilog.

It's common for a simulation or firmware to need data loading into a memory array. Fortunately Verilog provides the $readmemh and $readmemb functions for this very purposes. Unfortunately there is a dearth of good Verilog documentation online, so using them can be harder than it should be. This article explains the syntax and provides plenty of examples, including how to do this in Xilinx Vivado.

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FPGA VGA Graphics in Verilog Part 1

FPGA VGA Graphics in Verilog Part 1

This tutorial series introduces video graphics programming using FPGAs, starting with creating a VGA driver and moving onto more advanced features including bitmaps, sprites and effects. FPGAs excel at high-speed I/O and custom logic: you'll be surprised how much you can achieve with a few lines of Verilog.

This series is designed around the Digilent Arty and Basys 3 boards. If you're using the Arty you also need the VGA Pmod (the Basys3 has VGA output built-in). Detailed requirements are given below.

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