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FPGA Based IBM-PC-XT

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Re: FPGA Based IBM-PC-XT

#21

Post by tverbeure »

haxxorfreak wrote: post #6

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.

I was about the comment the same. It adds a lot of authenticity to the whole game loading process!

Re: FPGA Based IBM-PC-XT

#22

Post by iberator »

ForOldHack wrote: post #14
haxxorfreak wrote: post #6

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.

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 con…

Why original IBM BIOS was requried for Xenix?!

Re: FPGA Based IBM-PC-XT

#24

Post by bit-hack »

plantinthebok wrote: post #19

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.

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.

Re: FPGA Based IBM-PC-XT

#25

Post by bit-hack »

snvzz wrote: post #7

Looks nice, but there's no license. Can't do a thing with this.

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.

Re: FPGA Based IBM-PC-XT

#26

Post by userbinator »

dlcarrier wrote: post #4

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.

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

Re: FPGA Based IBM-PC-XT

#27

Post by mk_stjames »

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...

Re: FPGA Based IBM-PC-XT

#28

Post by bit-hack »

mk_stjames wrote: post #27

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...

The main reason is just due to me knowing my own limitations. SRAM is really simple to interface with and i've not yet tried to write a DRAM controller since its much more complex. Putting SRAM on the board made me more confident about the project. I did have it in mind that I could try to use the DRAM in place of the SRAM at a later stage (as you suggest) as a good way to focus on learning how to use it.

Re: FPGA Based IBM-PC-XT

#29

Post by ForOldHack »

I would like to have a xt and at and 386 in this tiny form factor, to play Rogue on the X T and try to compile nethack on the 286 version of Xenix and the 386 version of Xenix. I know from experience it will never compile on the 8088 version of Xenix. It will wreck your OS and filesystem.

Re: FPGA Based IBM-PC-XT

#30

Post by ForOldHack »

iberator wrote: post #22
ForOldHack wrote: post #14

Earlier quoted context omitted.

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 con…

Why original IBM BIOS was requried for Xenix?!

We found out after the third try, that both the IBM and one of the clone BIOSes would run the install, and all of them would boot. ( And an OMTI Rll controller, supported... Dual hard disks too. ) I needed an assembly language program to much the speed up to 10mhz, and it still ran fine, right up to the 'make nethack' then 4 hours later...beeeep beeeep beep. OS not found. We never figured out weather it was a out of memory error or a temp file error ... But the OS was gone.
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