emulator: Eternal Computer
type: libretro
core_classification: community_fork
source: "https://codeberg.org/iyzsong/eternal-libretro"
upstream: "https://github.com/adriancable/eternal"
source_commit: "13adf143aea822ebc1ee23722a80e93a7979e4c9"
upstream_commit: "17c8ab87de7f308f48f4990ed62c48b86173797d"
profiled_date: "2026-09-17"
core_version: "0.0"
display_name: "Eternal Computer"
cores:
  - eternal
systems:
  - eternal-computer

notes: |
  Virtual machine for the Eternal Software Initiative architecture, a Subleq
  variant with indirect operands, a keyboard port, a console port, a wall
  clock at word 64 and a timer interrupt through word 0. Adrian Cable's
  reference machines are vm/vm.c (SDL3 framebuffer) and vm/vm_console.c,
  and the libretro core by iyzsong carries the same loop in libretro.c:186-222.

  Machine memory is a static array of 3<<27 words, 1.5 GiB, cleared again
  when the content is unloaded (libretro.c:360-364). The framebuffer is its
  last 800x512 words (libretro.c:9-13, 22-23), pushed to the frontend as
  XRGB8888 on every retro_run (libretro.c:330-334).

  The content is the whole machine image. retro_load_game copies the buffer
  the frontend hands over to word 0, refuses an image larger than memory and
  starts the interpreter on a thread (libretro.c:302-314). need_fullpath is
  false and the accepted extensions are capsule and bootimage
  (libretro.c:275-282). The upstream machines fread the same file into mem
  (vm/vm.c:45-48, vm/vm_console.c:32).

  A boot image comes out of tools/make_boot_image.py applied to a Subleq ELF:
  a boot block of text_start bytes, with the interrupt vector at word 0, the
  saved PC at word 1, the initial stack pointer at word 4, the framebuffer
  word address at word 6 and the constants 0, -1 and 1 at words 36, 38 and
  39, followed by the flat binary (tools/make_boot_image.py:34-68). The
  upstream repository ships capsules/vmlinux.bootimage.xz, ESI Linux with
  busybox, Doom, nano, lynx and htop in its initramfs, 110 MiB once
  decompressed. The frontend does not open xz, so the image is decompressed
  before loading.

  Nothing else is read. retro_set_environment registers the log interface and
  the keyboard callback and nothing more (libretro.c:238-249), and the core never
  asks for a system, save or content directory and opens no file itself.
  Keyboard events are translated to USB HID usage IDs and queued eight deep
  (libretro.c:36-184). Console output goes to the host stdout with write
  (libretro.c:205-206). A fetched C of zero halts the machine and asks the
  frontend to shut down (libretro.c:196-199). No savestate
  (libretro.c:336-339), no memory map, no audio.

files: []