Wipforth

Wipforth is a simple Forth implementation that runs in the WebAssembly virtual machine. It does I/O via memory-mapped peripherals, which are emulated in JavaScript.

• For the Forth kernel, see wipforth.wat
• For the JavaScript emulator, see emu.js
• For the Forth prelude, which is loaded at start-up, see prelude.f
• For a description of the peripherals, see the Peripherals section below.

Building and Running Locally

You'll need:

• WABT
• Guile (or bring your own HTTP server -- see note below)

To run, first compile the WebAssembly module:

wat2wasm --enable-threads wipforth.wat

Then run the development server:

guile server.scm

You should then be able to open http://localhost:8080 in a browser and use the system from there.

NOTE: The server is very simple and just serves the files with the cross-origin isolation headers required for SharedMemoryBuffer use. You could use any HTTP server that sets these headers.

You should definitely not use the development server to serve the application on the open internet; I just hacked it together for testing on localhost during development and it's probably hilariously insecure.

End-to-End Tests

There's a (fairly minimal at the moment) end-to-end test suite defined in tests.scm. To run it you'll need:

• Guile again (no substitute this time, sorry)
• guile-json
• Firefox

I'm also pretty sure it won't work on a non-POSIX system, though I haven't tried it.

Given that's all sorted, you should be able to run:

guile tests.scm

It will print a JUnit XML report to standard out, you can pretty-print it with:

guile tests.scm | xmllint --format -

Though, of course, this will require that you have xmllint on your system.

Peripherals

Terminal

Name	Address	Size / B	Access
TXBUF	00h	32	write
RXBUF	20h	32	read
TXHEAD	40h	4	atomic read
TXTAIL	44h	4	atomic write
RXHEAD	48h	4	atomic write
RXTAIL	4Ch	4	atomic read

For both sending (TX) and receiving (RX), there are three registers: xBUF, xHEAD and xTAIL:

• xBUF registers are 32-byte FIFO ring buffers used for data
• The xHEAD and xTAIL registers specify the start and end of data in the ring buffer, xHEAD being the offset of the first byte of data, and xTAIL being the offset of the first byte after the data.

In order to be distinguishable from the empty state, the ring buffers must never be completely full -- there must always be at least one unoccupied byte between the tail and the head.

System status

Name	Address	Size / B	Access
SYSREADY	50h	1	atomic write

The SYSREADY register is used to indicate when the system has booted up and is ready for user input.