This repository is intended to become the official source for the reSID MOS6581 / MOS8580 SID emulator. However for now, I recommend fetching reSID from VICE :-)
reSID is widely used in two different incarnations - reSID 0.16, which was released in 2004, and a reSID 1.0 prerelease, which was included in VICE in 2010 - 2011, and has been patched by others since then. Unfortunately I never got around to make an official reSID 1.0 release.
I put in a lot of work to further reverse engineer the SID chip and advance the state of the art of SID emulation in 2010 - 2011. This work was in large part based on SID die shots, photographed and stitched by Michael Huth, and revectorized and annotated by Tommi Lempinen, with some further analysis by Frank Wolf. Several improvements were made in the digital domain, however the major achievement was vastly more accurate emulation in the analog domain by simulation of the actual analog circuits, using detailed models of DACs, VCRs, and op-amps. Op-amp transfer functions were obtained by feeding and measuring voltages directly on SID filter capacitor pins (with capacitors removed).
A few years later, in 2016, Leandro Nini (drfiemost) started the thread "Understanding the SID" on forum.6502.org. The goal was to do a complete reverse engineering of the SID chip, based on the same die shots I had worked with earlier. Dieter Mueller (ttlworks) was a major contributor to the reverse engineering effort. Leandro Nini's and Dieter Mueller's work resulted in detailed SID internals documentation and transistor level SID schematics. Leandro Nini even went as far as to create a complete transistor level simulation of the digital parts of the SID chip called perfect6581, based on perfect6502.
In this repository I am going to pick up from where I left some ten years ago, cherry picking from the reverse engineering mentioned above, patches in VICE, and my own research, with the goal of making reSID even better.
I also plan to use a refined reSID as the basis for an FPGA Verilog implementation for my take on a hardware SID replacement, the reDIP SID.