The MEGA65 on the net

I just stumbled across this three day old discussion about the MEGA65 in "Hacker News":

Mega65 – Open 8-Bit Computer

Quote from adtbm

But it's nice to see, that Paul and Shallan already answered there.

I think that Paul is everywhere on the net if someone mention "MEGA65"!

In the "Tokyo Retro Computer Users" meeting on May 15, 2021, a DevKit was present along with many other older computers.

Meetup #16 – 2021-05-15

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Greg brought along his Mega-65, the re-imagination of the Commodore 65 by some hardcore enthusiasts. The Mega-65 was having some graphical issues but it was at least running well enough to allow us to watch 3 Stooges.

In the Finnish retro magazin "Skrolli" issue 2021.1 you can find at page 56 a review of the MEGA65 DevKit.

Skrolli 2021.1

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- MEGA65 DevKit (Commodore 65:n uudet vaatteet) (s. 56)

Because it's a current issue and you still can buy it, there's only a very little thumbnail picture of the review on the net.

Maybe a Finnish fan has this issue and can read this review?

In the epsiode 273 (Published on April 30, 2021) of "The Retro Hour" you can listen 95 minutes to a audio stream about the Commodore 65 and MEGA65. You can also download the episode as a MP3 file on this site:

Commodore 65 & Mega 65 - The Retro Hour EP273

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The Commodore 65 was a cancelled super 8-bit computer from the early 90s, but in 2021 a team of hardcore fans have created a 21st century realisation of it. Running 40x faster than a C64 with some stunning modern features. We chat to project founder Paul Gardner-Stephen.

Here is a blog post by RGCD from February 13, 2021:

MEGA65 Devkit - First Impressions

In this videoclip Craig Walker shows how a MEGA65 case was printed:

This 4 weeks old thread in "Hacker News" started with a hint to the C256 but after a few comments there is also a branch with some posts about the programming of the MEGA65:

Thread in "Hacker News"

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Quote from hth313

I looked at the Mega65 with its three (not quite) 6502 CPU variants and I just found it so weird. Basically no 16 bit operations, instead a couple of 32 bit operations. Z register is no longer 0 and you have to set it non-zero to change bank configuration. Five instructions (nine bytes) to change bank and I do not understand how you can save the previous bank setting in case you want to restore it.

If you move the stack or zero page, the well known trick of using absolute plus index register no longer works the same as on the 6502 (breaking existing code). Sure, you could hardcode a different page, but the point of moving the stack is (probably) so you could do multi-tasking. But if processes are given different stack pages, they can no longer share code (if using such well known tricks in the code). Moving zero page is in 256 steps, so you cannot use it as a movable stack frame (the 65816 can set it to any location in the first 64K).

I know there is a lot of interest in the Mega65, but I found it had so many poorly made design decisions that made me want to stay far away.

So far I find the 65816 to a well designed 16 bits ISA (I am also familiar with PDP-11, MSP430, MELPS7700 and Motorola 6812) that gives a lot of 6502 vibes, but is just a lot better. There are a couple of odd corners, probably due to the opcode space as you mention, but I would not call it a bunch of compromises.

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Quote from cmrdporcupine

To be clear, the value (to me) of the MEGA65 is not that its CPU is superior. It's that the developers of the project are spending a lot of time on the hard part: cases, keyboards, software, and tooling.

They have GEOS running on it, they have backwards compat with the C64, they have games modified to use its extra capabilities, they have injected molded plastic cases, they have keyboards and keycaps manufactured, they have a version of the Kernal and BASIC ported and expanded, they have a user manual, etc.

And it's a) open source and b) open.

And b) is key because they're also making it possible for their hardware to be used with other FPGA bitstreams, including ones developed for the MiST/MiSTer. They demoed their hardware being used with a GBA core running a GBA game.

Further, they seem to have a CC65 backend -- I don't know of what quality -- but it seems C based software is running on it.

That makes it an interesting and more complete platform and consumer product.

And if I want a better 6502 variant on it, I could do that myself and use one of the various 65xx variant cores out there, or write my own.

EDIT: And, yeah, from my perspective from just casually reading their docs is that the CPU in the MEGA65 is an 8-bit CPU with bank switching and a couple weird 32-bit ops. It's not a 16-bit machine despite.

But the thing about the 816 is that it's only _sort of_ a machine with a 24-bit address bus. It effectively just has a bank switching mechanism, but not external. Mensch really just bolted some stuff onto the front of the 65C02 and widened the accumulator and registers by 8 bits. But the 16-bit registers are a pain. I just wish he'd added some new registers (and a way of combining them) instead of having the mode switch.

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In this turkish speaking Amiga forum there is an extra section for the MEGA65:

Mega65 - AmigaTürk

I just stumbled across this Hungarian blog post dated July 30, 2021 about the MEGA65:

A Mega65 projekt

Here is the DeepL translation into English:

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The Mega65 project

2021-07-30

S-kami

Commodore's products have had a huge impact on the world of computing, especially the VIC-20 and the C64.

These became the first personal computers to sell millions of units worldwide. According to some sources, between 17 and 25 million were sold, but some sources report sales of 30 million.

Whatever the truth, the undisputed fact is that for many of us it was the first really big step in the world of computing and many people still think nostalgically of the good old C64.

Many people have tried to ride that feeling and somehow resurrect the machine, with several different emulators and alternatives available for almost all major operating systems, but almost every year there is some new plug-in, accessory, game console or minicomputer.

The Mega65 project, launched by MEGA - Museum of Electronic Games & Art, is a very interesting initiative in more ways than one.

It is not just an attempt to ride on this nostalgia factor or emulate a particular release, but to create a concrete physical machine that is completely publicly available and downloadable for everyone.

The Mega65 is therefore an open source hardware and software ensemble that offers full compatibility with all the C64 applications and games released to date, but is also an enhanced, next-generation Commodore.

Although the C64 has become quite well known, relatively few people know that there was a concept that tried to combine certain features of the Amiga computers and backwards compatibility with its great predecessor, thus killing two birds with one stone, and this would have been the otherwise very attractive looking C65.

The look of the MEGA65 is no coincidence, it was based on this design in one piece, of course with significant improvements to the hardware, but what exactly is it?

The CPU: 8-bit GS4510 - 48 MHz - an amazing speed, 40x faster than the original C64, according to their own claims,

128 KB of RAM expandable up to 128 MB

HD output

network support

two 9-pin Atari standard joy support

3.5″ floppy disk

SD card support

Cartridge support

open source FPGA implementation - anyone can look at the machine and even rewrite and enhance it

BASIC 10

The specification is a bit more concrete in English:

CPU: 48MHz GS4510 single-core, in-order, no-branch-prediction, no-cache, single-scalar, no-fpu, no-smd, no-HCF, non-pipelined, enhanced 4502 8-bit processor, with 32-bit ZP indirect and 32-bit far-JSR/JMP/RTS operations, 28-bit address space, fast hypervisor traps, virtual memory, IO virtualisation (coming soon).

Speed: Synthmark64 score: 44.5x (C64 = 1x). Bouldermark score: 29,970 (C64 = 313).

DMA: C65 DMAgic compatible DMA controller. Fills at 48MB/sec, copies at 24MB/sec, swaps at 12MB/sec.

Video Controller: VIC-IV advanced rasterised video controller, like the VIC-II and VIC-III no framebuffer. Native resolution 1920×1200 (192MHz pixel clock). Supports all documented VIC-II modes (hi-res, multi-colour mode, extended-background-colour mode, sprites) and VIC-III modes (bitplanes are in the process of adding). Independent horizontal and vertical hardware scaling allows text and graphics resolutions as high as 1920×1200 and as low as 60×38. Separate 256-colour palettes for sprites, bitplanes and character graphics, allowing upto 1,024 colours on screen without changing the palette in real-time. VGA output 12-bit (4,096 colours). The planned DVI/HDMI output will support 23-bit colour (8.3 million colours). Text mode extensions including proportional width characters, super-extended background colour mode, as well as the standard VIC-III extended attributes.

Sound: Dual soft-SIDs + dual 8-bit DACs.

RAM: 128KB RAM visible to VIC-IV, 32KB colour RAM visible to VIC-IV, 128KB ROM/RAM. 128MB of (extended) DDR2 RAM being worked on to be made accessible.

Media: D81 disk images from SD card (native VFAT32 file system support coming soon). Real 3.5″ floppy drive support pLanned. Standard loading speed without fast loader ~20KB second. Loading speed direct from
SD card 300 – 3000KB/second (1200 – 12000 blocks per second), depending on SD card.

Outputs: Joystick ports 1 and 2 (9-Pin Atari Standard), VGA, 10/100mbit Ethernet,Mono Audio (Stereo soon), USB, Micro USB. Planned: HDMI, analog video, extension port, maybe external floppy.

Inputs: USB (supports PC keyboards and adaptor cards), Micro USB, Ethernet, Micro SD slot, and coming soon: 3D accelerometer, on-board microphone and thermometer.

Operating System: MEGA-OS all-in-one hypervisor and compat operating system, including integrated freezer and task switcher, VFAT32 file system driver and inter-process communications.

Form factor: C65-like all-in-one. A laptop form is planned for a future release. Full-height 19″ rack option extra.

Supported FGPAs: Nexys4DDR (and soon) Nexys4PSRAM. These boards include a Xilinx Artix7 100T FPGA, which is a high-performance FPGA, much faster and larger than the Spartan FPGAs used in other retro computing projects. Unfortunately the old Spartan FPGA boards cannot run the MEGA65 core.

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