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Overview of the Oric system

A partial implementation of the Oric Atmos 48K (ATMOS48K).

Core library: Highbyte.DotNet6502.Systems.Oric.

Current capabilities

  • NMOS 6502 at 1 MHz with a shared PAL raster clock: 64 CPU cycles per line, 312 lines and 19,968 cycles per frame. The pixel renderer samples visible scanlines as the raster reaches them, preserving software-generated raster effects that temporarily alter display memory.
  • 48 KB RAM, the MOS 6522 at $0300-$03FF, and a 16 KB system ROM at $C000-$FFFF.
  • 6522 parallel ports, control pins, timers and IRQ handling.
  • The optional RGB-VSync-to-cassette-input modification can be enabled in the Oric configuration, with the established 12-cycle high and 260-cycle low CB1 waveform. It is disabled by default to represent an unmodified Atmos. Compatible Download & Run entries such as Oricium enable it for that launch so they can synchronize directly to the display without manual raster calibration. The assembly samples include a CB1- and Timer-1-synchronized raster-bar demo that follows a sine-wave path and temporarily changes HIRES paper attributes only while the ULA scans the affected rows. A separate cable-free diagnostic uses a deliberately offset free-running Timer 1 and paced text-row paper sweeps to exercise progressive rendering without CB1 or manual calibration.
  • AY-3-8912 register access through the VIA control pins and mono PCM audio for its three tone, noise and envelope channels.
  • The Atmos eight-by-eight keyboard matrix. Host arrow, modifier, editing, alphanumeric and punctuation keys map to their physical Oric keys. US and Swedish host layouts are supported, with automatic operating-system detection or an explicit selection in the Avalonia and Terminal configs. Swedish Å/Ä/Ö provide convenient access to the Atmos [, ] and \ keys, while common Swedish Alt/Option/AltGr symbol chords are translated to the corresponding Atmos keys. PC Alt and Mac Option map to the Atmos FUNCT key; PC Backspace and Mac Delete map to DEL. F12 remains the emulator machine-code monitor shortcut. Atmos BASIC control combinations such as Ctrl+T for CAPS/lowercase and Ctrl+C to interrupt a program use the host Control key.
  • Copying the tokenized Atmos BASIC 1.1 program as source text and pasting clipboard text through the ROM keyboard input path. BASIC keywords must be uppercase, as on the real machine.
  • Parsing multi-file byte-level Oric .tap images and directly loading BASIC or machine-code records into RAM, including load-address and auto-run handling. A virtual tape cursor also feeds standard Atmos ROM CLOAD calls in sequence, so programs can load later records from the same tape. The Avalonia tape section can attach or replace an image without loading it, eject or rewind it, show the byte position and current/next file, and move safely to the previous or next parsed file boundary. Embedded BASIC examples cover text, hires graphics, sound effects, three-voice music, and AY tone/noise/envelope control.
  • Avalonia Download & Run support for a curated set of Oric programs from Oric.org and official project sources. TAP images may be downloaded directly or extracted from a named entry in a ZIP archive, are cached by the host application, and are started through the standard Atmos ROM cassette routine. The Browser host routes these downloads through its configured CORS proxy.
  • PASE/Altai/Mageco and IJK/Stingy/Egoist printer-port joystick interfaces, each with two Atari-style joystick sockets. A host gamepad can drive either socket, and optional keyboard joystick controls use W/A/S/D plus Space. While keyboard joystick is enabled, those keys are consumed as joystick input and are not also delivered to the Oric keyboard. The interface and socket selections are available both in the Avalonia sidebar and the Oric configuration dialog.
  • Remote control supports keyboard and joystick injection, paced text entry, BASIC readiness and source queries, direct TAP loading, and insert/rewind/eject/status control for the virtual tape.
  • Emulator-state snapshots preserve the CPU, 48 KB RAM, VIA timers and interrupts, AY register and generator phase, PAL raster and renderer phase, and any inserted TAP image and tape position.
  • The 240 × 224 active display in text and 240 × 200 hires modes, including serial ink, paper, character and screen attributes, alternate character sets, inverse and flashing characters, and the three text rows below hires graphics.
  • Avalonia Desktop and Avalonia Browser integration, with ROM and audio configuration.
  • Terminal integration with a 40 × 28 glyph-command text display, keyboard input, BASIC copy/paste, virtual tape controls, joystick configuration, and ROM download/selection. The Terminal host has no audio or hi-res pixel output.

Not yet implemented

  • Cassette pulse input/output, tape recording/CSAVE, and software that bypasses the Atmos ROM with a custom pulse loader. Because the current transport is a logical byte stream rather than a timed cassette signal, physical Play/Stop and continuous fast-forward/reverse controls do not apply.
  • Microdisc or Jasmin floppy controllers and disk images.
  • Printer output and Oric-specific monitor commands.
  • Cycle-level ULA bus contention, sub-scanline pixel fetch timing, and analogue AY output filtering.
  • The Oric-1, Oric-1 16K, Pravetz and Telestrat variants.

Snapshots

Oric .d6502snap snapshots restore the full Atmos execution state and embed an inserted TAP image, so a cassette operation can continue from the captured byte position. The raster resumes at the captured scanline and cycle, while the pixel and terminal renderers rebuild their presentation from the restored machine state.

ROM bytes are not stored in a snapshot; the destination uses the Atmos ROM from its current configuration. When snapshot configuration is included, the portable block also carries audio, VSync modification, joystick interface, keyboard-joystick, and CPU compatibility settings. A snapshot restored through a host application remains paused until explicitly started.

ROMs

The Atmos needs one copyrighted 16 KB firmware image. See ROMs for the accepted image, checksum, storage locations and the download acknowledgement.