Version 5.1 - June 28, 2024

The main purpose of this release is to support the new 2024 version of the MEGA65 (aka "R6") which sports enhanced hardware and better compatibility for Commodore 64 cartridges. Moreover, this release also delivers improvements for all MEGA65 models such as improved sound-over-HDMI compatibility, bugfixes such as the "long-reset bug" and it improves the compatibility of the core with demanding demos. Last but not least it makes the MEGA65's Real-Time-Clock (RTC) available in GEOS.

New Features: 2024 MEGA65 only

• Heavily improved quality of the analog audio output via the 3.1mm audio jack thanks to utilizing MEGA65's new audio DAC.

• The hardware of the MEGA65's Expansion Port (aka cartridge port) is now 100% compatible to the C64's hardware as it has bi-directional signals for RESET, IRQ and NMI. The C64 core is currently only leveraging the bi-directional signals for RESET, but this allowed us to make the core compatible with even more cartridges. Three examples that stand out are: (1) You do not need the
  "reset workaround" for the Kung Fu Flash (KFF) any more that is documented for the R3 board in doc/cartridges.md. (2) Reset buttons and "special" buttons at most freezer cartridges are working now. (3) MSSIAH works.

New Features: All MEGA65

• The MEGA65's Real Time Clock (RTC) is now able to power the date/time in GEOS as soon as the appropriate GEOS driver is installed. From a technical perspective, we are simulating the "CP-Uhr F83" by Jörg Sproß which uses a PCF8583 chip that is connected via the tape port.

• You can now close the "About & Help" screens also by pressing Run/Stop.

Improved HDMI Compatibility: All MEGA65

• Some monitors (e.g. the Philips S-line 275S1AE) did not output audio when displaying HDMI. The problem was related to a parity error in the IEC60958 channel which is fixed now.

• Fixed random micro cuts of sound that occured on on some HDMI displays. (Fixed GitHub issue #13)

Improved C64 Accuracy & Compatibility: All MEGA65

• Added VIC-II compatibility fix from MiSTer by gyurco which improves the core's compatibility with several demos (Fixes GitHub issue MiSTer-devel/C64_MiSTer#160)

• Improved disk change detection for multi-disk demos. This fixes for example Royal Arte/Booze Design. (MiSTer's GitHub issue 160 was "re-used" for this fix which is completely independent from the above-mentioned one, this is why we are linking to a specific comment: MiSTer-devel/C64_MiSTer#160 (comment))

Bugfixes: 2024 MEGA65 only

• HDMI backpower is no issue any more

Bugfixes: All MEGA65

• The "long-reset" feature was broken in V5. (Fixed GitHub issue #79)

• Fixed missing ".." in folders created with certain macOS versions (Fixed GitHub issue #111)

• Fixed a crash in the file browser. (Fixed GitHub issue #95)

• Stabilized the REU simulation. This fixes a known glitch plus it ensures that the REU simulation will run more stable also on the newer HyperRAM revisions that are built into 2023 and 2024 batches of the MEGA65: Treu Love demo: Fixed very rare REU/HyperRAM issues (GitHub issue #55)

• In V5 we introduced a new feature: You can go one menu-level up (from a sub-menu to the main-menu) by pressing Run/Stop. Subsequently you can also close then the main menu via Run/Stop (additionally to via Help). But if you did so, the Run/Stop keypress that happens to close the OSM was propagated to the C64. (Fixed GitHub issue #80)

• The "Audio improvements" feature only worked with analog audio (3.5mm jack) but not with digital audio via HDMI. (Fixed GitHub issue #100)

• MEGA65's internal floppy drive kepts spinning when a floppy was inserted. (Fixed GitHub issue #110)

Version 5 - June 23, 2023

Hardware support release: Insert hardware cartridges into the MEGA65's Expansion Port or simulate cartridges via *.crt files. Connect IEC devices such as drives and printers and enjoy Stereo SID sound. For an authentic retro feeling, feed a 15 kHz CSYNC video signal into your monitor or use the MiSTer VGA to RGB SCART cable to connect an old TV. Load faster using JiffyDOS or by directly loading *.prg files.

New Features

• Hardware cartridges can be used in the MEGA65's Expansion Port. Most game cartridges are supported and also many Flash Cartridges (e.g. EF1, EF3, KFF) and some more sophisticated utility cartridges and freezers are supported (see cartridge documentation).

• Run simulated cartridges by loading *.crt files from your SD card. Most cartridge types are supported. Saving data on the cartridge is not yet supported.

• Ability to directly load *.prg files.

• Ability to switch Kernal versions: Standard, C64 Games System, Japanese Revision and JiffyDOS.

• Stereo SID support: You can choose from multiple real dual SID combinations and enjoy stereo SID tunes and demos. And you can also use "pseudo stereo" by running the two different SID models 6581 and 8050 at the same (one left and one right) while they play the same mono tune.

• Hardware IEC port: Attach real 1541 & 1581 drives as well as printers, plotters or modern devices such as the SD2IEC and the Ultimate-II+.

• Support for three VGA output modes: Standard VGA, 15 kHz retro RGB output with either horizontal & vertical sync signals or with a composite sync (CSYNC) signal. The latter one allows you for example to connect the MEGA65 to an old SCART TV using the MiSTer VGA to RGB SCART cable or to connect it to an old monitor using a standard VGA to BNC cable.

• More clearly arranged menu system using submenus.

• Possibility to scale-down the On-Screen-Menu (OSM). Use-case: Compensate for large overscans of certain retro Cathode Ray Tubes.

• File browser's page up/down (cursor left/right) now jumps to the very first item when you press cursor left one (more) time while you are on the first page and to the very last item when you press cursor right one (more) time while you are on the last page.

• A long reset is now visualized: The power led is glowing blue as long as the user keeps the reset button pressed during a long reset.

Improved C64 and C1541 Accuracy & Compatibility

• Improved the 6510 CPU's interrupt dispatching which results in more demos working flawlessly (for example "All Hallows' Eve", this fixes
  #9).

• Improved accuracy of the frequency ratio between the C64's CPU and the C1541 floppy's CPU which results in more demos working flawlessly (for example "Unbounded" by Demotion and "Ice Cream Castle" by Crest). It also fixes an issue with the diskmag "Input 64" (#2).

• Merge MiSTer upstream fixes to improve simulation accuracy and compatibility with real hardware:

  • CIA: Disk parport: Ignore inputs on pins configured as output (MiSTer commit 4da804c, fix by sorgelig)
  • CIA: Fix timer reset values: Game "Arctic Shipwreck" works now and therefore this fixes MiSTer-devel/C64_MiSTer#107 (MiSTer commit 7eca7e3, fix by gyurco)
  • VIC: Change xscroll and turbo latch time (MiSTer commit f3a137b, fix by sorgelig)

Improved HDMI Compatibility

• Works with more HDMI monitors, frame grabbers, HDMI switches, etc. The core was not compliant to section 4.2.7 of the HDMI specification version 1.4b: It did not assert the +5V power signal. Now it does assert the +5 power signal via the FPGA pin ct_hpd.

• Fully dynamic flicker-free HDMI, which reduces our output latency on HDMI to less than 1ms and also eliminates the artifact, that moved from the top to the bottom of the screen every once in a while.

Bugfixes

• Fixed a bug in the REU simulation that affected some owners of the newest MEGA65 batches who have a so called "Revision D HyperRAM". One effect of the bug was that these users were not able to play Sonic the Hedgehog.

• Fixed the possibility of corrupting currently mounted D64 images: If the user changed menu settings while the core was writing to a D64 disk image (yellow MEGA65 drive led), then there was the possibility that this very D64 disk image would be corrupted.

Under the Hood

• Updated to Vivado 2022.2 which will result in higher quality bitstreams.

• Migrated to the newest version of the MiSTer2MEGA65 framework. The C64 core will benefit from an easier and faster workflow when it comes to migrating new framework features to the core.

• Now using glitch-free clock multiplexers: The user can switch the "HDMI: Flicker-free" mode ON/OFF without the system performing a reset.

Version 4 - November 25, 2022

Productivity release: Write support for the virtual C1541 and a 512 KB RAM Expansion Unit (1750 REU) are the main features: Save your high-scores and your gaming progress to disk (D64) and work productively with GEOS by speeding up 10x using the REU and by saving your work persistently to disk. Demo fans can now enjoy all the awesome REU releases on CSDB and gamers can play the fantastic Sonic the Hedgehog for REU.

New Features

• C1541 write support using D64 image files on the SD card.

• Read/write support for non-standard D64 images with 40 tracks and no error bytes, i.e. additionally to D64 files that are exactly 174,848 bytes in size you can now also use files that are 196,608 bytes in size.

• 1750 REU support: The REU is as close to cycle accurate as it can go. It is not perfect, but 99.9% perfect - it even runs the picky TreuLove_ForReal1750Reu.d64 version of Booze Design's Treu Love demo (see CSDB page) that is supposed to only run on real hardware. The REU also works perfectly with GEOS. You can switch the REU on/off using the options menu.

• Choice between 16:9 or 4:3 HDMI output resolutions: By default the core outputs 720p on HDMI which is a 16:9 resolution (even though the actual C64's output is pixel-perfect 4:3 as we are adding black bars left and right). With this new feature you can switch from 720p to 576p aka PAL over HDMI (720x576 pixels) and then select if you have a 4:3 monitor or a 5:4 monitor and then enjoy the best possible image.

• Ability to save the configuration settings of the core. You need to copy the file c64mega65 to the folder /c64 to activate this feature.

• CIA: New option to configure CIA version (6526 or 8521): There is at least one demo known - XXX from Lethargy - where the demo only runs flawlessly if the CIA is a 8521.

• Mouse: Support for C64 mice and MouSTer

• Reduced joystick latency from 5ms to 1ms by decreasing the stable time of the signal debouncer.

Bugfixes

• The drive led is not blinking any more during normal read/write operations. It behaves now like the real drive led and only blinks on errors.

• Fixed a small (probably inaudible) SID bug by merging this an upstream fix from MiSTer.

• Fixed several bugs in the file browser that you use for mounting D64 files:

  • The file browser was not able to display the "+" sign due to a bug in the font. Instead, a space (empty character, " ") was printed, for example the file name "C64+" was shown as "C64 ".

  • Directories where not aways being sorted in proper alphabetical order and ascending numbers.

  • While browsing directories with a large amount of subdirectories (e.g. large game libraries): When you entered a subdirectory located on a page other than page one (e.g. by scrolling down quite a bit) and then left this very subdirectory (one level up), then the selection cursor jumped back to page one.

  • Fixed file browsing bug that still displayed the old SD card's directory when you changed the SD card while the file browser was not open. (The bug did not occur when you changed the SD card while the file was open.)

Known problems that we plan to fix in Version 5

• Formatting disks does not work. We know how to fix it but this will need a larger refactoring (see "Technical Roadmap" in ROADMAP.md).

• The demo "All Hallows' Eve" (https://demozoo.org/productions/314618/) is crashing towards the end of disk 2. We fixed the issue in an experimental core that you can download here on GitHub: #9

• There is a compatibility issue due to the "HDMI: Flicker-free" mode. We only saw it occur at the German disk magazine "Input 64 Issue 1/85" and at the 1991 demo Unbounded by Demotion (https://csdb.dk/release/?id=2464). We fixed the issue in an experimental core that you can download here on GitHub: #2

Version 3 - June 27, 2022

This version is mainly a bugfix & compatibility release that is meant to
heavily increase the C64 compatibility of the core. It also adds support
for Paddles.

New feature

• Support for Paddles added: Connect compatible paddles to the joystick ports.

Bugfixes

• CIA Bug fixed: The bug prevented demos like Comalight and Apparatus to run
  and in games like Commando, the joystick's fire button did not work.

• CIA Bug fixed: "icr3 set priority over clear", merged from from MiSTer to
  our codebase. This bug prevented games like Arkanoid to run.

• User Port "low active" bug fixed: The bug prevented games like
  Bomberman C64, that support a Multiplayer Joystick Interface
  (https://www.c64-wiki.com/wiki/Multiplayer_Interface), to work. Reason is,
  that due to the low-active nature of the User Port these games detected
  "ghost activites" on the (not existent) joystick connected via User Port.

• Zero Page register $01 has the correct default value $37 now. It had the
  wrong value $C7 due to two bugs that have been fixed:
  (a) The Cassette Port's s SENSE and READ input are low active.
  (b) The wrapper code that turns the 6502 into a 6510 contained a bug.

Version 2 - June 18, 2022

This version is mainly a bugfix & stability release: The focus was not to add
a lot of new features, but to make sure that the C64 core works flawlessly
with more MEGA65 machines than version 1 did. We also added a DVI option
(see below) to increase the amount of displays that work with the core.

Bugfixes

• MAX10 reset bug fixed: Fixes the "ambulance lights" problem when starting
  the core and fixes non-working reset buttons
• SD card problem fixed: When neither any D64 file was present on the SD card
  and additionally, there was not a single subdirectory, then the core
  crashed with "Corrupt memory structure: Linked-list boundary" when one tried
  to mount a disk.
• Fixed distorted On-Screen-Menu in "VGA Retro 15KHz RGB" mode

DVI Option

• The DVI option is meant to improve the compatibility with certain monitors.
  Choosing "HDMI: DVI (no sound)" in the On-Screen-Menu will activate it and
  thus stop sending sound packages within the HDMI data stream.

Version 1 - April 26, 2022

Experience the Commodore 64 with great accuracy and sublime compatibility
on your MEGA65! It can run a ton of games and demos and it offers convenient
features.

Features

• PAL standard C64 (running standard KERNAL and standard C1541 DOS)
• PAL 720 x 576 pixels (4:3) @ 50 Hz via VGA: for a true retro feeling
• 720p @ 50 Hz or 60 Hz (16:9) via HDMI: for convenience
• Sound output via 3.5mm jack and via HDMI
• SID 6581 and 8580
• MEGA65 keyboard support (including cursor keys)
• Joystick support
• On-Screen-Menu via Help button to mount drives and to configure options
• C1541 read-only support: Mount standard *.D64 via SD card to drive 8
• Drive led during virtual disk access
• CRT filter: Optional visual scanlines on HDMI so that the output looks more
  like an old monitor or TV
• Crop/Zoom: On HDMI, you can optionally crop the top and bottom border of
  the C64's output and zoom in, so that the 16:9 screen real-estate is
  utilized more efficiently. Great for games.
• Audio processing: Optionally improve the raw audio output of the system
• Smart reset: Press the reset button briefly and only the C64 core is being
  reset; press it longer than 1.5 seconds and the whole machine is reset.