Viewing profile — nand2mario

Thanks for mentioning z386. Much of its recent progress was made possible by the reverse engineering and disassembly of the original 80386 microcode ( https://news.ycombinator.com/…

Probably some protected mode logic bugs. Just need more time to debug through the boot process.

The memory pipeline just starts one cycle later than now. Effective address is calculated during the first cycle of the instruction. The microcode then waits for it to finish with …

I think there are two reasons we haven’t seen an FPGA FPU yet, especially for MiSTer. First, FPUs are complex and FPGA support for floating point is limited. There's DSP blocks for…

Doom (DOS extender games) is an easier protected mode application as it does not use complex page tables. Linux is much more complex.

Not really. The 386 does not have an interface to read the ROM direclty. Instead, it uses the Built-In Self-Test (BIST) to verify the ROM's contents. It's basically a checksum-like…

Yep. The microcode in real mode segment loading (as shown in the post) does not set the limit to 64KB. That is why returning to real mode with a large value like 4GB in limit gives…

Nice findings. For segment loads from memory, the entry point is actually shared between real and protected mode on the 386. The microcode branches later based on PE and does the e…

I was just trying to give a bit of historical context, but apparrently need to be more precise next time! 386 is the beginning of 32 bit. But it's mainly the pentium and 486 that r…

Author here. Happy to discuss the technical details. The broader goal is to understand the 80386 microcode and hardware, and build an FPGA core around it, similar to what was alrea…

Right. Or it could be frequency illusion. Once you become aware of something, it appears to be more frequent: https://en.wikipedia.org/wiki/Frequency_illusion

xtce_trace sounds fantastic — exactly what I need right now while debugging my Verilog 8086 core. Thank you also for the microcode disassembly. It’s been fun to work through.

It currently uses 44% of the LUTs and 59% of the BRAMs (out of 340 × 2 KB blocks). The chip itself is fairly large and inexpensive, though performance leans toward the lower side.

Yes, for exactly the reason. SDRAM is much easier to work with in retro computing than DDR.

Author here. You’re right—EDO or FPM would be correct for the era. But as others have noted, DDR3 is fundamentally different from early 1990s memory, and it simply won’t run at the…