Sometimes you need to send a single pulse from one clock domain to another. This is a simple case of clock domain crossing or CDC. This FPGA recipe uses the xd module from the Project F Library to handle such situations simply and safely. Get in touch: GitHub Issues, 1BitSquared Discord, @WillFlux (Mastodon), @WillFlux (Twitter) NB. Additional content will be added to this post over summer 2022. Sponsor My Work Read more

The iCE40 UltraPlus distinguishes itself from the rest of the iCE40 FPGA family by including a relatively generous 1 Mb (128 KiB) of single port synchronous SRAM known as SPRAM. SPRAM blocks are much larger than BRAM but are limited to a single port and 16-bit data bus. In this quick FPGA recipe, we learn how to use SPRAM with Yosys and contrast it with Block RAM. If you want to learn more about other FPGA memory, see FPGA Memory Types. Read more

In this FPGA recipe, we’re going to look at a straightforward method for generating sine and cosine using a lookup table. There are more precise methods, but this one is fast and simple and will suffice for many applications. This post was last updated in October 2021. This post is part of a series of handy recipes to solve common FPGA development problems. There are also posts on fixed-point numbers, division, and square root. Read more

The square root is useful in many circumstances, including statistics, graphics, and signal processing. In this FPGA recipe, we’re going to look at a straightforward digit-by-digit square root algorithm for integer and fixed-point numbers. There are lower-latency methods, but this one is simple, using only subtraction and bit shifts. This post was last updated in June 2021. This post is part of a series of handy recipes to solve common FPGA development problems. Read more

Designing with FPGAs involves many types of memory, some familiar from other devices, but some that are specific to FPGAs. This FPGA recipe gives a quick overview of the different flavours, together with their strengths and weaknesses, and some sample designs. This guide includes external memory types, such as SRAM and HBM, that are used in CPUs and GPUs, so much of what is said here is generally applicable, but the focus is on FPGAs. Read more

Division is a fundamental arithmetic operation; one we take for granted in most contexts. FPGAs are different; Verilog can’t synthesize division: we need to do it ourselves. In this FPGA recipe, we’re going to look at a straightforward division algorithm for positive integers and fixed-point numbers. For integers, this method takes one cycle per bit: 32 cycles for 32-bit numbers. This post was last updated June 2021. This post is part of a series of handy recipes to solve common FPGA development problems. Read more

To work with standard monitors and TVs, you need to use the correct video timings. This recipe includes the timings for four standard display modes using analogue VGA, DVI, HDMI, or DisplayPort: 640x480 (VGA), 800x600 (SVGA), 1280x720, and 1920x1080 all at 60 Hz. CRT monitors typically support higher refresh rates in addition to 60 Hz, such as 72 and 85 Hz, but most LCD monitors do not. There are an increasing number of televisions and monitors that do support high refresh rates, but these are beyond the scope of this guide. Read more

Sometimes you need more precision than integers can provide, but floating-point computation is not trivial (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 fast; we can take advantage of that with a fixed-point approach. This post was last updated in May 2021. Read more

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