[HN Gopher] FPGA Based IBM-PC-XT
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FPGA Based IBM-PC-XT
Author : andsoitis
Score : 122 points
Date : 2025-11-16 15:26 UTC (7 hours ago)
(HTM) web link (bit-hack.net)
(TXT) w3m dump (bit-hack.net)
| inglor_cz wrote:
| Wow. A lot of memories unlocked instantly. My first PC in 1995
| was a very old IBM PC XT.
| Lio wrote:
| Yeah I had a little Carry-I PC XT clone with CGA/Hercules
| graphics, V20 8088 and an amber screen that I really regret
| selling.
|
| I guess it couldn't really do that much at the time compared to
| Amigas, STs and Acorns but there was something magic about my
| experiences with the PC.
| hintbits wrote:
| Same. I had a used Amstrad PC 1640, which had V20 @ 8Mhz and
| EGA graphics. The author's desire really hit home here.
| hintbits wrote:
| correction: it had v30, which was 8086 rather than 8088 clone
| (16bit bus)
| dlcarrier wrote:
| The title is a bit misleading; it's running on an 8088-compatible
| CPU, and a 1 megabyte SRAM, with the FPGA containing the display
| adapter and drive controller, as well as the glue logic.
| II2II wrote:
| A bit misleading, albeit in an impressive way. I nearly skipped
| the article thinking that it would be an all FPGA solution.
| Instead, they interfaced somewhat period correct chips: the V20
| was used in XT compatibles of the era, the DAC was authentic
| (even if it is only a small part of the sound card), and the 1
| MB RAM chip is the sort of cost cutting measure they would have
| used back in the day if it was available (though it would
| likely have been DRAM rather than SRAM). The rest being on an
| FPGA is certainly understandable since it was listed as an FPGA
| based project!
| ssrc wrote:
| And the FPGA is a modern day equivalent to an ULA. If they
| could have put all of the chips in a single programmable one,
| they would.
| nsxwolf wrote:
| This build demonstrate what's actually interesting about FPGA
| to me. A pure implementation might as well be a software
| emulator. Being able to interface real chips makes this really
| neat.
| userbinator wrote:
| Indeed, this should be more correctly described as an FPGA-
| Based IBM PC/XT _Chipset_.
|
| In contrast, here's a whole 486-class PC compatible on an FPGA:
| https://github.com/alfikpl/ao486
| haxxorfreak wrote:
| I love the hard drive sound emulation! I find that modern
| restorations of vintage hardware using SD cards to emulate drives
| are missing an important part of the nostalgic experience when
| they just start up completely silently.
| ForOldHack wrote:
| The floppy disk usually made this straight up honking noise . I
| had a V20, but at 10Mhz. Never had a problem, except for
| formatting floppies. The V20 has a few tricks up it's sleeve,
| with a few less clock cycles on some instructions, and a Z80
| mode to run cpm.
|
| But,the real trick was to put real IBM roms in a clone board
| and run Xenix. When the clone roms are back in it still booted.
| Helped a lot to have a 2:1 Rll controller. Xenix was just
| pollute and delute - system V with some BSD thrown in and a
| slightly altered portable C complier that was later admitted to
| be wrong endian.
|
| Did this Board have a FPU socket? Made turbo pascal run much
| faster. ( The 8087 version we got from the physics lab...)
| Especially the Hilbert matrix. And FFTs.
| iberator wrote:
| Why original IBM BIOS was requried for Xenix?!
| tverbeure wrote:
| I was about the comment the same. It adds a lot of authenticity
| to the whole game loading process!
| snvzz wrote:
| Looks nice, but there's no license. Can't do a thing with this.
| smokel wrote:
| Marvel and enjoy.
| fortyseven wrote:
| Jesus christ, must everything be transactional?
| bit-hack wrote:
| Thats an oversight on my part, I should put a license on it. I
| would love for anyone to be able to build one or tinker with
| the code as they want to. After all I was only able to make
| this because others shared their projects that I could learn
| from.
| ForOldHack wrote:
| Well, we have a dos clone and FFTs I. The news... Can this run
| the DOS clone and do FFTs?
| kvemkon wrote:
| Dupe. Posted few days ago by author:
| https://news.ycombinator.com/item?id=45903083.
| plantinthebok wrote:
| What was the most surprising timing constraint you had to meet
| for the V20 bus controller? The 8088's multiclock cycles were
| always under specified in original datasheets and I'm curious
| what reality looked like.
| bit-hack wrote:
| The bus controller was fairly straight forward. I found the
| timing diagrams in the V20 datasheet to be pretty easy to
| follow. The clock for the CPU is generated by the FPGA which I
| derived from a clock running at twice the speed, that made it
| easy to pick which clock edges I wanted to sample from or
| assert data for the CPU on. I did have a bug or two in there
| early on which meant that memory writes would not store the
| data I was expecting as I sampled the data bus at the wrong
| time. That was a tricky one as the bug would only become
| visible when that location was loaded from again. The CPU i'm
| using is rated for 16Mhz, but i've only tried to push it up to
| 10Mhz so far so I have a bit of margin. Some more issues might
| pop up if I push the speed higher I suspect. Its very stable as
| it is now and i've not seen any issues I could attribute to the
| bus handling.
| asdefghyk wrote:
| A bit offtopic for this article , but I'm waiting for some FPGA's
| based "..device PC emulator?..." that can connect to my old hard
| drives from the mid 80s ... and boot them ....
| mk_stjames wrote:
| There is 32MB of SDRAM on the FPGA board.... I wonder exactly
| what using 1MB of that as the system memory would have entailed
| instead of the separate 1MB SRAM chip that had to be soldered.
| Was using the extra SRAM chip just done just to do it, or is
| there a specific reason there that I'm not
| seeing/understanding...
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