Given the technical specs of the FPGAs available to hobbyists these days, it really shouldn’t be a shock that you can implement a relatively-modern chipset on one, like one for a 486 system. In spite of knowing that in the technical sense, we were still caught off guard by [maniek-86]’s M8SBC project that does just that– the proas both CPU and BIOSducing a 486 FPGA chipset with a motherboard to boot.
Boot what? Linux 2.2.6, MS-DOS 6.22 or FreeDOS all work. It can run DOOM, of course, along with Wolfenstien 3D, Prince of Persia, and even the famous Second Reality demo– though that last without sound. [maniek-86]’s implementation is lacking direct memory access, so sound card support is right out. There are a few other bugs that are slowly being squished, too, according to the latest Reddit thread.Continue reading “M8SBC-86 Is An FPGA-Based “Kinda PC Compatible” 486 SBC”→
In the 1980s there were an incredible number of personal computers of all shapes, sizes, and operating system types, and there was very little interoperability. Unlike today’s Windows-Mac duopoly, this era was much more of a free-for-all but that didn’t mean companies like Microsoft weren’t trying to clean up all of this mess. In 1983 they introduced the MSX standard for computers, hoping to coalesce users around a single design. Eventually it became very successful in Japan and saw some use in a few other places but is now relegated to the dustbin of history, but a new FPGA kit unofficially supports this standard.
The kit is called the OneChip Book and, unlike most FPGA kits, includes essentially everything needed to get it up and running including screen, keyboard, and I/O all in a pre-built laptop case. At its core it’s just that: and FPGA kit. But its original intent was to recreate this old 80s computer standard with modern hardware. The only problem is they never asked for permission, and their plans were quickly quashed. The development kit is still available, though, and [electricadventures] goes through the steps to get this computer set up to emulate this unofficially-supported retro spec. He’s also able to get original MSX cartridges running on it when everything is said and done.
Although MSX is relatively unknown in North America and Western Europe, it remains a fairly popular platform for retro computing enthusiasts in much of the rest of the world. We’ve seen a few similar projects related to this computer standard like this MSX-inspired cyberdeck design, but also others that bring new hardware to this old platform.
Over the years there have been a few CPUs designed to directly run a high-level programming language, the most common approach being to build a physical manifestation of a portable code virtual machine. An example might be the experimental Java processors which implemented the JVM. Similarly, in 1976 Itty Bitty Computers released an implementation of Tiny BASIC which used a simple virtual machine, and to celebrate 50 years of Tiny BASIC, [Zoltan Pekic] designed a CPU that mirrors that VM.
The CPU was created within a Digilent Anvyl board, and the VHDL file is freely available. The microcode mapping ROM was generated by a microcode compiler, also written by [Zoltan]. The original design could execute all of the 40 instructions included in the reference implementation of Tiny BASIC; later iterations extended it a bit more. To benchmark its performance, [Zoltan] set the clock rate on the development board equal to those of various other retrocomputers, then compared the times each took to calculate the prime numbers under 1000 using the same Tiny BASIC program. The BASIC CPU outperformed all of them except for Digital Microsystems’ HEX29. Continue reading “Designing A CPU For Native BASIC”→
For the retro gaming enthusiast, nothing beats original hardware. The feel of the controllers and the exact timing of the original, non-emulated software provide a certain experience that’s difficult or impossible to replicate otherwise. To that end, [bit-hack] wanted to play the original EGA, 16-color version of The Secret of Monkey Island in a way that faithfully recreated the original and came up with this FPGA-based PC with a real NEC V20 powering it all.
The early 90s-style build is based on a low-power version of the V20 called the V20HL which makes it much easier to interface with a modern 3.3 V FPGA compared to the original 5 V chip. It’s still an IBM XT compatible PC though, with the FPGA tying together the retro processor to a 1 MB RAM module, a micro SD slot that acts as a hard disk drive, a digital-to-analog audio converter, and of course the PS/2 keyboard and mouse and VGA port. The mouse was one of the bigger challenges for [bit-hack] as original XT PCs of this era would have used a serial port instead.
With a custom PCB housed in a acrylic case, [bit-hack] has a modern looking recreation of an XT PC running an original processor and capable of using all of the period-correct peripherals that would have been used to play Monkey Island when it was first released.
This build goes a bit of a different route to many other DIY keyboards out there, in that [Lambert] was keen to build it around an FPGA instead of an off-the-shelf microcontroller. To that end, the entire USB HID stack was implemented in VHDL on a Lattice ECP5 chip. It was a heavy-duty way to go, but it makes the keyboard quite unique compared to those that just rely on existing HID libraries to do the job. This onboard hardware also allowed [Lambert] to include JTAG, SPI, I2C, and UART interfaces right on the keyboard, as well as a USB hub for good measure.
As for the mechanical design, it’s a full-size 105-key ISO keyboard with one bonus key for good measure. That’s the coffee key, which either locks the attached computer when you’re going for a break, or resets the FPGA with a long press just in case it’s necessary. It’s built with Cherry MX compatible switches, has N-key rollover capability, and a mighty 1000 Hz polling rate. If you can exceed that by hand, you’re some sort of superhuman.
Tang FPGA boards are affordable, and [nand2mario] has been trying to get an x86 core running on one for a while. Looks like it finally worked out, as there is an early version of the ao486 design on a Tang FPGA board using a Gowin device. That core’s available on the MiSTer platform, which emulates games using an Altera Cyclone device.
Of course, porting something substantial between FPGA architectures is not trivial. In addition, [nand2mario] made some changes. The original core uses DDR3 memory, but for the Tang and the 486, SDRAM makes more sense. The only problem is that the Tang’s SDRAM is 16 bits wide, which would imply you need two cycles per 32-bit access. To mitigate this, the memory system runs at twice the main clock frequency. Of course, that’s kind of double data rate, but not in the same way as DDR memory.
Does the in 65F02 “F” stand for “fast” or “FPGA”? [Jurgen] doesn’t know, but his drop-in replacement board for the 6502 and 65c02 is out there and open source, whatever you want it to stand for.
The “f” could easily be both, since at 100 MHz, the 65f02 is blazing fast by 6502 standards–literally 100 times the speed of the first chips from MOS. That speed comes from the use of a Spartan 6 FPGA core to implement the 6502 logic; making the “f” stand for “FPGA” makes sense, given that the CMOS version of the chip was dubbed the 65c02. The 65f02 is a tiny PCB containing the FPGA and all associated hardware that shares the footprint of a DIP-40 package, making it a drop-in replacement. A really fast drop-in replacement.
You might be thinking that that’s insane, and that (for example) the memory on an Apple ][ could never run at 100 MHz and so you won’t get the gains. This is both true, and accounted for: the 65F02 has an internal RAM “cache” that it mirrors to external memory at a rate the bus can handle. When memory addresses known to interact with peripherals change, the 65f02 slows down to match for “real time” operations.
The USB adapter board for programming is a great touch.
Because of this the memory map of the external machine matters; [Jurgen] has tested the Commodore PET and Apple ][, along with a plethora of German chess computers, but, alas, this chip is not currently compatible with the Commodore 64, Atari 400/800 or BBC Micro (or at least not tested). The project is open source, however, so you might be able to help [Jurgen] change that.
We admit this project isn’t totally new– indeed, it looks like [Jurgen]’s last update was in 2024– but a fast 6502 is just as obsolete today as it was when [Jurgen] started work in 2020. That’s why when [Stephen Walters] sent us the tip (via electronics-lab), we just had to cover it, especially considering the 6502’s golden jubilee.
