Commodore 64 Emulator v0.8.4.6-alpha

Commodore 64 Emulator v0.8.4.6-alpha is released. A Commodore 64 emulator written in modern C++, built with SDL2 and designed around two priorities:Accuracy-first emulation (with a strong focus on real hardware behavior over “good enough” hacks); Debuggability (integrated monitor, break/watchpoints, and visibility into what the machine is doing). This project is actively under development; expect rough edges and incomplete features.

Commodore 64 Emulator Changelog:
This release focuses heavily on VIC-II accuracy, CPU/VIC timing, stability, media handling, and emulator architecture.
A major part of the work over the past two weeks has been moving additional VIC-II behavior away from scanline-level approximations and toward more accurate cycle-based execution.
Highlights
Major VIC-II fetch and graphics pipeline improvements
Fixed significant graphics issues in RoboCop 3
Fixed a graphics regression in Dig Dug
Resolved an Action Biker raster IRQ regression
Improved sprite pointer, DMA, MC/MCBASE, and Y-expansion handling
Improved bad-line and background graphics fetch sequencing
Improved CPU/VIC bus arbitration and interrupt timing
Corrected NMOS 6510 KIL/JAM behavior in the micro-op CPU path
Improved repeated T64/datasette loading
Hardened emulator shutdown against intermittent access violations
Continued save-state compatibility and versioning improvements
Continued SID oscillator/state architecture work
Expanded VIC-II and CPU diagnostics in the built-in monitor
Fixed regression from last release where old palette was loaded during SDL 2 to 3 upgrade
VIC-II Improvements
The VIC-II execution pipeline received substantial timing and architecture work.
Graphics Fetch Pipeline
Background graphics accesses are now handled during the VIC fetch phase rather than being coupled to later rendering activity.
Graphics sequencer advancement now occurs after the appropriate graphics memory access.
This provides more accurate ordering between:
VIC memory accesses
CPU bus availability
graphics sequencing
sprite activity
register changes
Sprite Fetch Timing
Sprite pointer fetching has been moved to the correct fetch-slot timing.
This fixed cases where sprite data could be fetched using stale or incorrect pointer values.
Additional sprite-related work includes:
Sprite DMA sequencing improvements
MC/MCBASE timing improvements
Y-expansion behavior refinements
Sprite pointer fetch timing corrections
Improved sprite state diagnostics
Bad-Line and Register Timing
Additional work was completed around:
Bad-line fetch sequencing
D011 timing
D016 timing
D018 timing
mid-frame VIC register changes
graphics sequencer state
raster event tracking
Compatibility Fixes
RoboCop 3
Fixed major graphics corruption affecting multiple RoboCop 3 screens.
The issue was traced primarily to the ordering of:
background graphics fetches
sprite pointer fetches
graphics sequencer advancement
Sprite pointers are now fetched at the proper VIC fetch-slot boundary and background graphics accesses occur during the appropriate fetch phase.
Dig Dug
Fixed a graphics regression uncovered during VIC-II sequencing changes.
Action Biker
Resolved a raster IRQ comparator regression that caused screen flashing.
Eye of the Beholder
Corrected micro-op CPU behavior when encountering NMOS 6502/6510 KIL/JAM instructions.
Additional graphics compatibility work for this title remains ongoing.
CPU / 6510
Continued improvements to the cycle-accurate micro-op CPU implementation.
Changes include work around:
interrupt recognition timing
RTI behavior
RDY/AEC stalls
CPU/VIC arbitration
stalled instruction fetches
undocumented instructions
KIL/JAM behavior
cycle-level tracing
SID
Continued restructuring of the SID implementation.
Work in this release focuses on keeping behavior that is common to all SID revisions separate from future model-specific behavior.
Additional work was also completed around SID save-state versioning and oscillator state handling.
Save States
Continued improvements to the save state architecture. Any existing save states will not work with this release due to the changes for the SID. Going forward from this release, compatiiblity will be maintained with future releases.
Media / Datasette
Improved repeated T64 loading.
Previously, attaching another T64 while one was already active could overwrite machine state or leave the C64 in an unsuitable state for launching the next program.
Media switching now performs a safer reset/load transition and avoids the emulator freeze encountered during repeated T64 attachment.
Added T64 index selection if there is more than one program to the UI.
Updated UI to show various live statics when using the datasette.
Stability
Improved emulator shutdown and component teardown.
Shutdown now more deliberately disconnects callbacks and cross-component references before components are destroyed.
Areas updated include:
video callbacks
audio shutdown
monitor/debug connections
virtual modem devices
user-port devices
trace managers
cartridge references
chipset references
Run-loop changes also eliminated a reproducible access violation encountered when closing the emulator window introduced in the last release.
Cartridge / Expansion Hardware
Continued cartridge and expansion-device cleanup.
Work includes:
mapper reset-state auditing
continued EasyFlash state review
improved cartridge initialization/reset behavior
moved REU menu from the system menu to the peripheral menu
Monitor / Diagnostics
Expanded the built-in machine-language monitor to assist with cycle-sensitive debugging.
VIC diagnostics now provide increasingly detailed visibility into:
raster and cycle position
VIC registers
color registers
VIC memory banks
screen/character/bitmap locations
sprite DMA state
sprite MC/MCBASE state
sprite pointers
register-write events
raster event summaries
raster IRQ state
CPU tracing and execution diagnostics were also expanded.
Monitor formatting was reviewed to prevent persistent C++ stream settings such as std::setfill() from leaking into later commands, especially help output.
Internal Cleanup
Additional cleanup was completed across the CPU, VIC-II, machine lifecycle, and component interfaces.
This included:
dead-code removal
reducing public API surface
removing obsolete timing paths
separating fetch/render responsibilities
improving component ownership
improving shutdown boundaries
consolidating machine wiring
simplifying future timing work
Known Areas Still Under Development
This remains an alpha release. Active accuracy work continues in areas including:
VIC-II sprite timing
raster IRQ edge cases
PAL/NTSC timing differences
mid-scanline register writes
multicolor graphics edge cases
CPU/VIC arbitration
SID model-specific behavior
cartridge and expansion hardware accuracy
Summary
v0.8.4.6-alpha is primarily an accuracy and stability release.
The most significant improvements are in VIC-II memory-fetch sequencing, sprite timing, CPU/VIC interaction, media handling, save-state robustness, and emulator shutdown stability.

Download: Commodore 64 Emulator v0.8.4.6-alpha
Source: Here