How zxplay_go compares to other ZX Spectrum Next emulators

This document compares zxplay_go with the three most prominent ZX Spectrum Next emulators: CSpect, ZEsarUX, and MAME (its tbblue driver).

It is written and maintained by the zxplay_go project, but the goal is a fair and accurate picture, not a sales pitch. Two honesty notes up front:

• Feature presence ≠ maturity. A green check means "implemented," not "as battle-tested as a tool that thousands of people have shipped games on for years." CSpect and ZEsarUX have large user bases and a long track record; MAME is the community's accuracy/preservation reference. zxplay_go is young and its focus to date has been reference-faithful OS boot and hardware correctness rather than broad commercial-title compatibility.
• Data is as of mid-2026, gathered from each project's public sources (repositories, official docs, the SpecNext community wiki, and DeZog's documentation). Where a fact could not be confirmed from public sources it is marked ❔, not guessed. Corrections via pull request are welcome.

Legend

Columns: zxplay_go · CSpect · ZEsarUX · MAME (tbblue driver).

1. Project & licensing

¹ Upstream project code is MIT; this repository's modifications are GPLv3, and the bundled FPGA boot ROM (tbblue_loader.rom) is GPLv3, so this tree is distributed under GPLv3 as a whole. The licensed NextZXOS system ROMs are not bundled — see §6. ² CSpect is a closed-source personal "devkit"; the author states there is no support and that redistribution is not permitted.

2. Platforms

³ Native binaries for Linux arm64 and macOS arm64; Windows arm64 is experimental. ⁴ MAME has an ARMv8 recompiler back-end and official Windows-ARM64 binaries.

3. Machines emulated

⁵ ZEsarUX emulates +2A/+3 but disk support is DSK-focused. ⁶ MAME is a multi-system emulator covering tens of thousands of machines; ZEsarUX covers a very wide range of 8-bit/16-bit home computers. zxplay_go and CSpect are focused on the Spectrum family / Next. ⁹ Pentagon 128: 128K paging + AY with no memory contention and the 71680-T Pentagon frame; boots its editor ROM to the 128 menu and runs 128/48 BASIC. The TR-DOS / Beta-disk interface (WD1793 + auto-paging TR-DOS ROM) loads .trd images on the Pentagon (and the 48K/128K); .scl is not yet supported. ⁷ zxplay_go runs the genuine ZX80 (4K) and ZX81 (8K) ROMs with a faithful CPU-generated display, so each machine uses its own native keyword layout (e.g. PRINT is on O for the ZX80, P for the ZX81). .P / .O programs load. ¹⁰ SAM Coupé (MGT, 1989): boots the bundled MGT ROM 3.0 to SAM BASIC; all four screen modes, the 128-colour palette + CLUT, SAA1099 stereo sound, the WD1772 floppy with MGT/SAD images (real disk games boot — verified with Manic Miner and Tetris), ASIC memory/IO contention, the light-pen registers, and the frame/line interrupts. --sam or Machine → SAM Coupé. See docs/sam-coupe.md.

4. Spectrum Next video hardware

⁷ MAME implements the collision bit; the "max sprites per line" status bit is a documented TODO. zxplay_go implements collision and the max-per-line status flag; the per-line bandwidth render limit is visual-only and deferred. ⁸ Copper in zxplay_go is driven from a per-T-state beam-position model but rendered per-scanline (full per-pixel hpos deferred). CSpect/ZEsarUX Copper timing is documented as sub-scanline-imprecise. ⁹ ULANext palette handling in zxplay_go is wired for the static-palette paths the OS boot exercises; per-scanline ULA palette writes are deferred.

All four emulators describe their Next graphics pipeline as a work in progress; cross-emulator and on-hardware verification is the norm.

5. CPU & timing accuracy

¹⁰ ZEsarUX documents "almost all" Z80N opcodes. ¹¹ zxplay_go targets cycle accuracy with contention that scales by turbo multiplier; the boot path is byte-identical to the FPGA reference at 3.5 MHz. Exhaustive per-software timing validation is ongoing. ¹² CSpect is explicitly described (by the community and author) as functionally accurate but not cycle-exact. ¹³ MAME's tbblue driver has memory contention as an explicit TODO (its classic Spectrum drivers do model contention). This is the clearest single accuracy gap of MAME's Next driver. ¹⁴ zxplay_go's boot path was verified divergence-by-divergence against the FPGA core's behaviour; a GHDL gate-level testbench is deferred research. ¹⁵ MAME's tbblue is a near-line-by-line translation of the official FPGA VHDL, which is why the community treats it as the accuracy reference.

6. Boot, media & file formats

¹⁶ MAME boots NextZXOS to navigable menus; full Browser use is highly likely but was not photographically confirmed in this survey. ¹⁷ zxplay_go can mount a host directory (building a FAT image on the fly) or a pre-built .img/.mmc. ¹⁸ The licensed NextZXOS ROMs (Amstrad/Sky copyright) are downloaded on demand from the official distribution rather than bundled. ¹⁹ MAME's Next machine removes the snapshot device; it has no .nex loader. ²⁰ CSpect loads tape mainly via the emulated SD/NextZXOS path; TZX is not natively decoded. ²¹ On the Next machine MAME's tape/floppy devices are vestigial (the real Next has no tape/floppy port); MAME's classic +3 driver has a full FDC. ²² zxplay_go supports RZX playback and recording, including competition-mode DSA signing/verification.

7. Peripherals

²³ zxplay_go persists battery-backed RTC NVRAM to disk. ²⁴ zxplay_go implements the zxnDMA's memory↔memory and memory↔IO transfers (sprite/Layer 2/DAC port endpoints), per-byte prescaler + cycle-length timing (continuous-mode duration charged to the CPU clock; burst-mode + prescaler transfers interleaved with the CPU so DMA-streamed audio is paced across the CPU timeline), Continue / auto-restart, and read-mask register read-back. ²⁵ zxplay_go provides a UART/AT-command stub; real Wi-Fi networking is out of scope. ²⁶ None of these emulators run a real ESP8266 Wi-Fi firmware stack; they model the UART and optionally bridge to host serial / a real device.

8. Audio

⁸ Classic-Spectrum SpecDrum (port $DF) and Covox (port $FB), opt-in from the Peripherals menu. Event-timed: each DAC write is recorded with its T-state offset and reconstructed per audio-sample (like the beeper), so PCM playback is sample-accurate rather than a per-frame snapshot.

9. Debugging & developer tooling

²⁷ zxplay_go has two surfaces — a live GUI debugger and a scriptable telnet server — over one shared backend (breakpoints, watchpoints, time-travel, M1 trace ring). ²⁸ In CSpect, conditional breakpoints are typically evaluated by DeZog rather than natively. ²⁹ zxplay_go offers a snapshot ring with rewind (not continuous reverse execution). ZEsarUX's "time machine" is the most complete reverse-debugging implementation here. ³⁰ zxplay_go exposes a custom line-oriented telnet protocol; it is not DeZog/DZRP/ ZRCP-compatible. ³¹ MAME's GDB stub is i386-only and cannot debug the Z80, so it is not usable for Next debugging; MAME instead offers a strong native debugger plus Lua. ³² zxplay_go has no plugin API, but offers extensive headless trace/automation flags.

10. Maturity & positioning

Honest summary

Where zxplay_go stands out today: it is a clean, fully open-source (MIT upstream; GPLv3 as modified here) Go implementation that cold-boots NextZXOS faithfully, models Next memory contention and sprite collision (areas where some rivals have gaps), ships both a GUI and a scriptable telnet debugger over a shared backend, and uniquely supports RZX recording with competition-mode signing among this group.

Where the others lead: CSpect is the emulator most Next developers actually use day-to-day, with a mature plugin ecosystem and first-class DeZog support. ZEsarUX has the broadest machine coverage, the most complete reverse-debugging ("time machine"), notable accessibility features, and years of refinement. MAME is the FPGA-faithful preservation reference with deep, well-documented tooling.

If you are writing Next software today, you will likely still reach for CSpect or ZEsarUX (and verify on real hardware). zxplay_go's aim is to be a correct, readable, open reference implementation — and on the specific axes of faithful OS boot, contention modelling, and an open codebase, it already compares well.

Spotted an error or an out-of-date row? Please open an issue or PR.