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I built this MP/M computer using Teensy 4.1, which uses a modern PC type keyboard via "USBHost_t36.h" and attached to Teensy. Works great. I tested it through a hub and that works too. But I've got one person trying to attach their keyboard through a KVM, and the USB keyboard is not being...

No, it's clear as mud. A couple people have asked for this. I'm missing a "spec sheet"! I will do this...

OK! Friendly fZ80 Computers are now for sale on eBay: https://www.ebay.com/itm/205876956191

OK they're "done" haha. Complete enough to be shippable, they seem solidly reliable and I've got 10 I will post on eBay on Wednesday 26 Nov 2025. If someone here wants one let me know ASAP, before they go on eBay. Or if you prefer, contact me and I can inform you when they are available on eBay...

Yeah, sorry to undo all your work!! Except for the three-arg write, nothing I've changed is incompatible. I just needed to get out from under this bug. It's now quite repeatable so I can revisit it later when. fZ80 doesn't use as much stack as "modern" code -- I've written embedded crap for so...

OK! I uploaded the correct released files and fixed some broken links. The upgrade process, for all the changes, is just re-flash, copy the contents of one of the bundles onto your A: drive, SYSBOOT the new CBIOS.HEX, and press reset. Fixed up the project page. The manual, a nice PDF, is...

Aargh the release has a bad MP/M XIOS in it, interrupts off (a test copy). Will fix today. Sorry for that. Will let you know.

I wrote this up for myself, to go into the source. But it tells the tale above. linearly. At the moment I'm using a very stripped out version of VGA4BIT, which I'd done initially looking for bugs that might write into my Z80 banks in the same RAM2 memory, like out of bounds array reference (it...

Yeah it's very weird. Now CP/M doesn't do this! And the Teensy code is the same! CP/M also has a (very simple) timer tick. ANd it can run multi-window, or not, so that code isn't it. This is why I was so baffled! I couldn't see how it wasn't MP/M related, which means 8080 code, or D.R.s code...

Didn't fix it.

OK will do! Oh, I don't actually *understand* the VGA/DMA code! lol. Honestly I haven't tried; I worked around it; I have a ton of krap to do to get out from under this grown-insanely project! But I will not forget it. I've snapshotted a version of my code that has the problem, and I'm fairly...

Sure you want flat black? I use Montana paints, the graffiti folk use them. Amazing colors. Here's the choice, lol. https://www.montanacolors.com/en/productos/mtn-94-aerosol-spray-paint/ I've been thinking something bright, and period-incorrect. Vivid red, Kalani orange, Electra violet...

I've been working almost (no, not almost, ...) obsessively getting the fZ80 reliable. I had a huge random-memory-corrupt error, a true heisenbug, that I finally traced solidly to interaction between the IntervalTimer object and something in the FlexIO2VGA DMA and/or interrupt. I spent a month...

Wow! OK that's a lot. I think there's something really interesting here. Is there some sort of p-code machine you could write/find an efficient interpreter for? And make a dense, succinct general purpose machine from? With high level "primitives" like your display and filesystems you could...

Cool. I'm finishing up the current revision. It's quite a lot of work done. Reliability all around is up, as is performance. MP/M II 2.1 is half way to usable in a modern sense. I'm editing in one window, compile and test in another, and can be looking at another file in a 3rd, with the other...

Touche! My slower response! lol I had not been keeping track of card format, FAT16, FAT32, etc. Regarding the SD card read error, SD_CARD_ERROR_CMD18, frequently reported when accessing either of the removable SD cards... I had them wired in parallel (bussed) with separate selects of course...

F1 through F12 are the window-changing keys. I think F12 brings up the big cross cursor. You've run VGA M to get into multiwindow mode? You see four windows? F1..F4 selects window 1..4. In the version you have, F12 should bring up the resize cursor (big screen sized +) and arrow keys move it...

I think the current Teensy design is great. The funny port write resolves my weird corner cases. One of the major complaints from computer folk at the time (I was probably one of them; I just don't remember) about the IBM PC's and workalikes was the lack of a reset button on the front panel...

I've got a project that is externally USB powered AND has the USB cable from the Teensy to the development machine. I have to unplug two cables to power it off. During debugging it's a PITA to do that. I've built a computer with emulated CPU that is a "black box" computer, and it is possible to...

Ahh... OK that's a feature of C++ I've never used, wasn't thinking of those extentions to the Serial object. I had modified write() to take the x and y args directly, inlined pixel writing, and did a number of unrelated things to speed performance and cut memory use (I've used the entire...

Ahh. It's in VGA4bit, built on FlexIO2VGA. There are some virtuals (write). I'm not clear on what virtuals are; I'll go rtfm and report back.

I'm running into seemingly-random occurrences of undefined reference to 'vtable for FlexIO2VGA' when adding or removing functions that seem quite mundane and operating on local vars only. I tried various optimizations, didn't change. I'll go look at the annoucements. EDIT: I installed beta...

As note there, I've got that stack-move core code in place and running, will report back. Thanks!

Ahh, I didn't know about the no mans land. I just went through all the code, easy enough, to see what heap arrays I'm using. Only one function has more than a couple hundred bytes, but looking at them, the functions that do so are all mutually exclusive, so I'll reduce that to two I think static...

Yeah, metoo, I may be (accountably) running out of RAM, specifically stack space a tool to see this would be amazing! Just posted this https://forum.pjrc.com/index.php?threads/teensy-4-1-stack-size-and-memory-usage.77343/

The project is a banked-memory emulated-Z80 computer, running MP/M II 2.1, display is done with @wwatson's VGA_4BIT library which uses some 400K for the DMV display, 1024 x 768.

My current project, nearing "final" release, has used pretty much all of the megabyte of memory. For a few weeks I'm having very sporadic, mostly unrepeatable errors in execution that I've been assuming were my bad code, but now I'm thinking, after narrowing it down behaviorally, that it's a...

Wow! That's a lot!! And they look really great, like 90's unix! And great news on the bug fixes. I've not had a single issue that I'm aware of. But I'm not directly using any *box drawing stuff, and not even putchar, just write. So maybe I've side-stepped them. But I'll get and test with the...

Oh sorry, somehow I missed your post! Yes, every feature of the Z80 is implemented, including "documented undocumented" side effects. I did not write the emulator, @davidly did, it passes all known to me Z80 test suites, of which there are many.

Here's the entire "interface" for resizing! The black gap in the image above has the cursor (drawn with | - and + characters) in the gap, draggable. I'll rummage around in the charset to find line drawing characters; is there a displayable list of them?

OK, a did a thing. I wrote a window manager in Teensy, split the screen into four, with a big "cursor" that divides the screen. Hit F-+ to enter resize, draw the cursor with arrow keys. Programs can be running. The Z80 thinks it had four "Heath/Zenith H89" terminals (selectable via IO port)...

I looked at drawpixel after I posted, sorry! should have looked first. .... Not a big deal. I am storing color per character, and will make a little state machine do set..color before calling write as needed. The x 2 is 2 bytes per character, char and color. A window is then 3 dimensions. A...

Here's a sketch of the scheme. The pen line is the screen, the lighter pencil four 24x80 windows, the rightmost two dangling over the edge. A simple case. The cursor thingie of course consumes character cells, but is probably necessary. I'm thinking different background or foreground color in...

Wow! Very nice! All of the scroll bugs are gone. I'm using the T4_FIXES version, has the main one been updated? I went in another path, and implemented four 24 x 80 character windows, that can be mapped to the screen. Each is a full H19 escape sequence machine. Each terminal is 24 x 80 x 2, so...

Sure! Well "type it in" into a .ASM source file and compile with ASM.COM or equiv, and follow the usual CP/M rules, yes. Or you could literally just type them in, directly to memory, using DDT.COM. I've done this. It accepts Intel mnemonics. ZSID.COM would accept Zilog mnemonics. (I prefer the...

Another way might be to leave the DMA'd portion of the design as-is to shuffle pixels to the screen, which it's already very good at; and do all windowing at the character level. Currently-active window could be the one with the cursor. Lines and cols is inherently rectangular, and within the...

New release, just now; has your FIXES version. I think the weird disk stuff is gone. Notes: https://www.bleeve.me/eZ80/Release/eZ80.3-11Jul2025/ReleaseNotes.11Jul2025

SOOOOoooo.... I just read all the MP/M II docs... and it would not be that hard to implement. It does real preemptive multitasking! On an 8080! The shop I worked at in the late 70s brought one up, MP/M 1, not II (2), with the off-application intent of doing what I am thinking now (which is what...

Not sure what you're asking? The Z80 sees everything as I/O ports, true. The z80 emulator calls Devices::inPort (n) and outPort (n, val) and the Teensy handles it from there. The teensy side code uses an event model. Each .h tab is a single object, with setup() and loop() entry points. The...

The one thing I seriously miss editing and compiling, not available on CP/M, is an edit window and a test/debug window. Constantly quitting and restarting is tedious. And a 768x1024 screen is just big enough to split... With Teensy handling the screen, it occurs to me that single-seat MP/M-80...

Oh, no hurry at all! Aha! I have not been paying attention to the filesystem type at all. I'll go look at mine. Exactly that. A: is the 4-bit SDIO so besides faster, it's electrically isolated. I didn't pay enough attention to the SD card electronics, but I'll revise the board shortly. I'll...

All's going well with the machine, and back from Tear Down, besides fixing bugs generally I am concentrating on SD cards. I wrote a disk (SD) tester, runs on the Z80 side, to stress test my code (blocking/deblocking and multidrive and buffering etc) and that test code has been a big help. I did...

To address your mentioning of the SD card error in the VGA thread... There is a sporadic problem when two SD cards are inserted at once. The mere presence of the second (on the SPI buss) card seems to cause problems with the first. I think I have a strategy to investigate, and I'll do so in the...

AH!!! Nice! OK got it, and that makes sense. So scroll does the tCursorOff() only if it's displaying at scroll time? So I can remove my explicit controls? I also did explicit tCursorOn() after moving the cursor so that it immediately displays in the new location, as opposed to having to wait...

Hey here's something to think about on your "cursor problem" -- I don't think it is -- vga4bit is usable as-is as a "glass tty", in ancient parlance. But it's a hell of a set of primitives for more sophisticated stuff, like emulating VT100 or in my case H19/H89. I recognize the...

Neato!! Thanks! Lol I always fear I send one to someone-not-me and it catches on fire or runs out the door or something. I'm in the Great Middle of the project -- most things work as intended, but I'm whacking bugs daily. As you know, working on H19 terminal emulation. Of course it being 1975...

I had to add explicit cursor control else they'd dot the screen with dead cursors. No big deal.

I cobbled your code into this test program with manual commands, so that I could watch how text xy moves. It appears to work correctly, maybe an off-by-1 in height but that could be easily fixed with the call to scroll, and its as likely my FU and I will look closely later after I have lunch...

OK cool! I will install the latest library and check this out. That was fast work! I'll try this out ASAP. If I have any issues, I'll write a small test program to replicate it. I've already thought that out.

It JUST occurred to me, I may be incorrectly visualizing what INSERT LINE is supposed to do!