skywater-pdk VS picorv32

Preferably Intel compatible or able to run Linux? Something I can build in my garage or in a simple microprocessor fab.

https://github.com/google/skywater-pdk

It looks neat, but the process node is 1 um with 3 metal layers.

The open Skywater PDK is 130 nm : https://github.com/google/skywater-pdk (though I don't know how reliable the PDK is?)

From working in a somewhat related discipline, the PDKs for the high end nodes (think tsmc N16 and lower) are quite hard to obtain and require your org to pass security audit. In addition to that the cadence licenses are priced very much for a big-org rather than a startup.

Does your chip absolutely need a modern node? I'm assuming you've seen the open source skywater pdk, but here it is just in case. https://github.com/google/skywater-pdk

If you need a free PDK, check out: https://github.com/google/skywater-pdk

That would be really neat, but I haven't seen anyone even make a CMOS imager on SKY130.

https://github.com/google/skywater-pdk

One could make an array of thermopiles, like the hacker that made their own imager out of discrete diodes (digiOBSCURA) . But each pixel would cost $7.

https://www.digikey.com/en/products/detail/excelitas-technol...

One might be able to make an array of thermistors (possibly with active cooling using a peltier) like the diycamera (digiOBSCURA) below. Might be an application of combining many RC oscillators in a tree and recovering the signal with an FFT. I have a gut feeling this is possible, but haven't show it.

https://www.digikey.com/en/products/detail/panasonic-electro...

https://github.com/IdleHandsProject/diycamera (digiOBSCURA)

One could experiment with microbolometers on tinytapeout. https://elicit.org/search?q=cmos+microbolometer

https://tinytapeout.com/

Unlike x86_64 which can only legally be produced by two and one-quarter companies, RISC-V is a permissively open-sourced ISA so anyone can make a chip. Literally, you can download Verilog of Berkeley Rocket cores from Github and run it on an FPGA, or prep it to send to SkyWater to fab at 130nm.

Taping out an actual chip inevitably involves IP that's not yours, e.g. the standard cell library and other 'physical' IP like memories and flash. You cannot open source that as it is not yours and in general the owners of it won't want to open source it either (though there are exceptions e.g. the Skywater 130nm PDK https://github.com/google/skywater-pdk).

In OpenTitan we've built all the 'logical' IP ourselves from the ground up. This is the Verilog RTL you can see in our repository but you need the 'physical' IP to make a real chip. We haven't built any physical IP so we need to get it from the traditional industry sources which means traditional industry licensing (i.e. very much not open).

In contrast to most people here saying you NEED to spend money. I disagree with that. You can implement and simulate a SPI master/slave fully on your computer, no FPGA or other hardware required. There are simulation models for SPI peripherals you could use. For example: https://github.com/YosysHQ/picorv32/blob/master/picosoc/spiflash.v

The Pico RV32 is pretty small, and can go as low as about 750 LUTs, with most features elided. I don't know how Xilinix LUTs translate to Lattice though.

Picorv32: https://github.com/YosysHQ/picorv32

There are loads of free RISC-V cores that you can read the source of and run on cheap FPGAs. Take a look at PicoRV32: https://github.com/YosysHQ/picorv32

picorv32 is written in Verilog.

In short: it works, though the implementation lacks the crystal clarity of FemtoRV32 and PicoRV32. The core is larger than SERV but has higher IPC and (very arguably) a more conventional implementation. The compressed instruction set is easier to expand into regular RV32I instructions than it is to execute directly.

That is, reducing the number of LUT required to implement a CPU of a given ISA.

A basic RV32 CPU is down to 500-700 LUT.

    https://github.com/YosysHQ/picorv32

I've bought a cheap FPGA board (Sipeed Tang Nano 9K) because I want to implement a little 8 or 16-bit CPU. The FPGA has plenty of BRAM for such a little CPU, so I wouldn't even need to implement an SPI controller initially, but I want to implement a von Neumann architecture, and was wondering if the only way of doing so using single port (or semi dual port) RAM would be to use 2 cycles or more for memory transfer operations (one for loading the instruction, one for executing the actual memory transfer), or if there was any technique that could be used to avoid this without having to implement instruction-level parallelism. Even if not, references to understandable code implementing a simple memory interface would be appreciated. I looked at PicoRV32 but couldn't really understand its inner workings.

Have you looked at PicoRV32? https://github.com/YosysHQ/picorv32

What I mean is that you use the FPGA fabric to implement a soft-core CPU, like MicroBlaze (Xilinx) or Nios II (Altera/Intel) or RISC-V or any other CPU you like. Then you can do the MP3 or WAV signal decoding in software, which will be orders of magnitude easier to do than to do it in hardware. For a media player, this is more than adequate.