The Hana 1 Soft Core

This repository contans a simulator for the Hana 1, soft core stack machine running a small interpreter and compiler in simulation.

Hana 1 is the newest member of the J1 family of stack processors. Hana 1 provides 16K 16 bit words of memory. Compared to the popular J1a, the Hana 1 has twice the memory, much larger stacks (256 vs 16 words), more hardware instructions, SPI access, a better bus, code folding, and a richer library, but requires 119 fewer LUTs, The J1a is larger because it implements the stacks in BRAMs. and requires a multiplexer to connect together 32 x 4Kbit block RAMs (BRAMs) into a single 8K word memory module. The Hana 1 is smaller because it implements the data and return stack in 2 BRAMs, and uses a 16K word hardcore single port RAM (SPRAM) to provide the bulk of the memory. The J1a cannot use the larger SPRAMs available on the more modern ICE40-UP FPGAs because the SPRAMs cannot be initialized in the bitstream, they require a bootloader. Hana 1 includes one BRAM initialized with a compute kernel, a boot loader, and uses 2 BRAMs for stacks, freeing up 27 other BRAMs for other uses. Would you like more stacks with your Forth anyone?

The Mecrisp Hayes Forth test suite was modified to run on the FPGA, and the system passed all tests. You can read more about the system in an article and a Master's thesis, hosted on a private channel on the pico-ice discord server. As soon as the publication ban expires in October 2024, the article will be posted here.

The Hana 1 was built by modifying the dual port Mecrisp Ice Verilog and Forth. Mecrisp Ice is built on top of SwapForth.

TODO:

1. Get the boot script working on the FPGA. Eventually, the pico-ice gateware will also be hosted here.

2. There are some Mecrisp tests that use an undefined word. I need to figure out what is going on there.

3. The Hayes (ANSI) Forth test suite allows, even causes stack overflow and underflow, Hana 1 is stricter. I am not quite sure what to do.

4. There are some additional compile switches I want to add. -static -static-libgcc -static-libstdc++ LDFLAGs

5. Add a beautiful makefile like this one.

6. Get the boot script working on the FPGA.