I downloaded https://github.com/Isotel/mixedsim and had a go at it, and it actually works for me. I was a bit surprised to find that the way it works is that it synths to X subcircuits, and includes a wrapper with the A XSPICE models. This has two reasons. One is that Yosys write_spice writes modules as X, the other is that they use this to sub in a CMOS implementation for slow analog sim. I think two interesting things could be explored: 1. expand the Yosys spice backend to write A XSPICE primitives directly. This would make it more easy to expand support for more of the supported cells. It can even do state machines and memory it appears 2. generate XSPICE implementations of Sky130 standard cells. This would allow the same kind of "retargeting" that isotel is doing, but specifically for simulating Sky130 mixed signal designs.