saladcore - A hybrid stack machine

Main characteristics

• fixed size 8-bit instructions
• variable precision literals via concatenation
• 16-level deep stack overflowing to memory
• direct stack access with PICK/MOV instructions (frame indexed)
• spare encoding space for custom / emulated instructions

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Implementation

Saladcore is a work-in-progress ISA. Currently a C simulator is available which can also be compiled to WASM. This was used to experiment with a custom Forth-like language, saladforth, making use of the frame instructions.

A Verilog implementation of a minimal instruction set is planned, and the current instructions are expected to change, to accomodate both the minimal hardware and the more fully-featured simulator, while not requiring major saladforth changes.

A demo including basic emulated hardware (a serial link and a 1-bit 128x128 display) is available at https://vsgab.github.io/demo/salad/

Usage

The WASM demo uses clang directly for compilation, so the Makefile defaults to it.
Useful targets:

• make dev runs ROM tester binary with fth/dev.sf as input source ; this loads the rom.bin file built previously, runs the reset code in the reset word ^^ and then interprets the source received over serial0 line by line
• make web creates a directory web in the output directory with the demo ; this needs to be served over HTTP
• make serve starts a python http.server serving the web directory locally

Future

• Minimal Verilog implementation → FPGA
• Expand demo to fully featured fantasy console
• Compile C to saladforth

References

[1] Microcore
[2] ZPU
[3] UXN
[4] "Tom Thumb" font