DEC MicroVAX 3900 (KA655) with OpenVMS VAX

Log in with SYSTEM / QUOKKA1953

The machine boots itself: the KA655’s self-tests first, then OpenVMS, about a minute to the Username: prompt. Click the terminal before typing.

The machine below is a DEC MicroVAX 3900, the Q22-bus VAX built around the KA655 CPU module: a CVAX 78034 at 3.125 MHz with the CFPA floating-point accelerator, the CMCTL memory controller, the CQBIC Qbus interface, and the KA655 console/diagnostic ROM at physical 0x20040000.

Attached devices:

• RQDX3 MSCP Disk Controller, with an OpenVMS VAX V5.5 system disk auto-mounted on DUA0:
• The console serial line on OPA0:, as a glass TTY — DCL and the boot stream render correctly, but screen programs (EDT, EVE, NOTES) do not paint

The disk image is fetched read-only; writes go to an in-memory copy-on-write overlay that vanishes when you close the tab. Set autoBoot="false" on the <cpu> element of machine.xml if you would rather stop at the KA655’s >>> prompt and boot by hand.

The port, the media it loads, and how to run it locally are described on the DEC VAX page.

Source

The VAX emulator is JavaScript, and all of it is readable:

• machines/dec/vax/ — the port
• modules/v2/ — the machine itself: cpu.js and decode.js for instruction execution, mmu.js for memory management, cqbic.js for the Qbus, rqdx3.js and rq.js for the MSCP disk controller that DUA0: is attached to
• tests/ — how it is graded. Most of these are differentials: they run the same instruction stream through this emulator and through Open SIMH and compare state register by register, rather than asserting against numbers somebody typed in.
• browser/ — the Web Worker the machine runs in, and the disk provider that fetches the volume over HTTP

It is ported site-for-site from Open SIMH’s VAX/ sources (MIT, © 1998–2019 Robert M Supnik), so a function here generally has a C original with the same name, and the comments say which one.

[GitHub Source]