FPGAs and microcontrollers often need to store some sort of configuration on SPI flash. Whereas we could always use external programmers or code or bitstreams to access the flash, various products have come up with a more clever solution: JTAGSPI. JTAGSPI tunnels SPI over JTAG, so that we can program our SPI flash using a basic JTAG programmer. Let’s see how to implement an OpenOCD compatible JTAGSPI solution in our JTAG TAPs. ...
Experienced developers have some intuition how a hardware description maps to circuits, enabling them to optimize code for circuit area or speed instinctively. But like most of the time, checking is better than (educated) guessing. ...
Open source EDA tools and open source PDKs for various technologies have recently matured a lot. Here’s a simple and quick way to set up the development environment for those and get started with development. ...
The Tang Nano 20K board programs the Gowin FPGA using the JTAG protocol. Reusing that JTAG connection for our applications means we don’t need an external JTAG probe for software debugging using NEORV32’s On-Chip-Debugger. ...
The Gowin series of FPGA support configuration pin reuse on some special dual-purpose pins. Those pins are used during programming of the FPGA, e.g. for JTAG or as READY and DONE signals. When enabling pin reuse, they can be used as normal GPIO pins by the FPGA bitstream after configuration. The OSS toolchain supports setting these flags and here’s how. ...
NEORV32 does not have any dedicated output pin for the SPI flash write protect signal. On boards like the Tang Nano 20K, not driving this pin however means we can’t write to SPI flash. This breaks the upload firmware function in the bootloader, so here’s how to fix this. ...
Cocotb is a convenient way to write your hardware verification tests in Python. Let’s see how to use it with the OSS toolchain. ...
The NEORV32 default bootloader has various configuration options. Here’s how to modify and recompile it. ...
Dev Containers is a convenient way to develop in VS Code, whereas distrobox enables convenient GUI and device access in containers. Both concepts can be combined using VS Code’s Attach to running container command, but there are some things to remember. ...
NEORV32 is an Open Source RISC-V SoC written in VHDL. The CPU neither the smallest nor the fastest RISC-V core, but its main benefit is the complete ecosystem: Not only does it provide peripherals such as I2C, SPI, GPIO and more. It also ships ready-to-use drivers and extensive developer and user documentation. And if bare-metal is not enough, it also offers a FreeRTOS port. Let’s see how we can port NEORV32 to the Tang Nano FPGA. ...