Paolo Amoroso's Journal

Tech projects, hobby programming, and geeky thoughts of Paolo Amoroso

Once the V20-MBC or Z80-MBC2 is plugged into a USB port of my Chromebox, starting a Minicom terminal emulator session makes the remote device boot up and display progress messages.

At some point, with the V20-MBC, starting Minicom did nothing and only the terminal printed its signon messages. The remote device wouldn't boot and there were no signs of life other than the lit LEDs.

The flat cable that runs from the V20-MBC ends in a serial-USB adapter with a USB connector that goes into the Chromebox. This is the adapter card with the USB connector at left and, at right, the pins the cable's connector plugs into:

Serial-USB adapter of the V20-MBC Nec V20 homebrew computer.

To troubleshoot the issue I unplugged the USB connector from the Chromebox, which is when the cable's connector came out from the pins. That made clear the issue was a loose plug. Plugging the adapter back into the cable, reconnecting to the Chromebox, and starting Minicom made the V20-MBC automatically boot up as usual.

#v20mbc #sbc

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Published links to the original sources of the media, quoted text, or other content shared online are increasingly less common. Not that they ever were much common.

Academia has always had a strong culture of crediting and referencing. And this is what the users with this background have been doing online since the early days of the Internet and the web. Most of those who still do are in academia or communities with similar values like bloggers and open-source developers. It’s a lost art, especially as more and more ordinary users come online.

Why take time and effort to link the sources?

The most obvious reason is fairness to the original creators of the content, who deserve recognition for their work. But there’s more to linking than crediting and fairness.

The references to the sources and other metadata are invaluable research tools.

They enable to track where ideas originate, how they spread, how influential they are. Metadata are essential for accessing the original content in its full form and the best available formats such as high-resolution images, complete videos, or the full text and context of quotes. References allow to explore the rest of the shared content and discover new ideas or overlooked portions of works.

But the most important reason for always providing full references and links to the sources is they enable uses not originally anticipated. The absence of sources makes all this unnecessarily difficult or impossible.

#misc

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Just4Fun, the maker of the Z80-MBC2 and V20-MBC homebrew computers, clarfied to me the absence of some files is intentional.

Under CP/M-86, the TOD.CMD command for displaying and changing the date and time was left out because, on the V20-MBC, the date can be changed only from the boot and configuration menu. ASSIGN.CMD, a command for assigning physical to logical devices, is specific to the CP/M-86 version for the IBM PC and hence redundant on the V20-MBC.

Just4Fun doesn't recall exactly, but the absence of the Turbo Pascal sample .PAS files on the Z80-MBC2 is likely a consequence of the development process, possibly an early mass storage space constraint.

#v20mbc #z80mbc2 #sbc

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Mastodon.technology, the Mastodon instance that hosted my account, will be shut down. The admin Ash Furrow took this decision for serious personal reasons.

As a Google+ survivor and a fediverse newbie with barely 7 months on Mastodon, the announcement startled me. I set out to find a good new home and now I'm on Fosstodon as @amoroso@fosstodon.org This instance is open to anyone interested in technology, with a focus on free and open-source software.

Fosstodon is culturally close to Mastodon.technology. Both have similar topics and values, and comparable user base sizes. Instead of a single maintainer like Mastodon.technology, a team of admins and moderators and more resources give Fosstodon some redundancy and assurance of longevity.

The Mastodon documentation explains the simple procedure for moving an account.

Creating an account on the new instance, transferring the data, and filling the profile was mostly seamless and took less than half an hour. Mastodon transferred my followers automatically, I only had to upload to Fosstodon the list of followed users downloaded from Mastodon.technology.

Although the process took care of my social graph, moving toots and media isn't supported and I could only download my old toots. Bummer, I hope the developers implement full content transfer soon.

#fediverse

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The V20-MBC homebrew computer I ordered finally arrived and I started checking it out.

The V20-MBC is a single-board computer by the same maker of the Z80-MBC2. Most of the design is common to both. However, unlike the Z80-MBC2, instead of a Z80 the V20-MBC has a Nec V20 chip that implements the instruction sets of the Intel 8080, which runs CP/M-80 2.2 on the V20-MBC, and the Intel 8088 with CP/M-86 1.1.

I got a V20-MBC Black Edition. It's a version of the V20-MBC with higher quality parts and a black PCB that, along with most of the other components also black, makes for a slick look:

V20-MBC homebrew computer.

I already love the device. These notes are my early impressions, but I'll continue sharing my experience with the V20-MBC.

Hardware

Both homebrew computers have similar size and layout and are accessed the same way, i.e. with a terminal emulator running on a desktop computer, a Chromebox in my case, connected via a USB serial line. Here is the setup, with the Chromebox at the top:

V20-MBC homebrew computer connected to a Chromebox.

The performance of the 8088 of the Nec V20 under CP/M-86 is noticeably better than the Z80-based Z80-MBC2. I estimate CP/M-86 software on the V20-MBC is 2-3X as fast as CP/M-80 programs on the Z80-MBC2.

Software

The V20-MBC is operated the same way as the Z80-MBC2, except for a couple of differences.

To account for the two CPUs, the boot and configuration menu duplicates the entries that load executable code. This is the menu in a Minicom terminal emulator session under Crostini Linux on the Chromebox:

V20-MBC boot and configuration menu.

There are two options for uploading an executable in Intel HEX format to run on the bare hardware with no operating system, iLoad for 8086 code and iLoad-80 for Intel 8080 code. Similarly, Autoboot automatically boots a designated 8086 binary, Autoboot-80 an 8080 one.

Although I never used CP/M-86 before, thanks to my prior experience with CP/M-80 the 16-bit operating system looks familiar and I already feel productive. Aside from the additional transient commands of CP/M-86, the only major difference is executable program files have the .CMD extension instead of .COM as on CP/M-80. This screenshot of the A: drive directory shows the extensions:

CP/M-86 session on a V20-MBC homebrew computer.

Issues

A quick check reveals some CP/M-86 files are missing, such as the TOD.CMD and ASSIGN.CMD transient commands. This is not unexpected as the Z80-MBC2 is also missing some files, e.g. STAT.COM and the Turbo Pascal sample .PAS sources. No big deal, it's easy to find and download suitable replacements.

#v20mbc #sbc #retrocomputing

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Back when the Pixel 4 XL was Google's latest Android flagship, JR Raphael wrote a great piece on the insanity of smartphone screen notches and holes: The enduring absurdity of our smartphone bezel obsession. He pointed out the compromises punching holes into and cutting out screen areas in the name of no bezels imposes for little or no design gain, which often defeats the whole point of making those changes in the first place.

In the later article No, the Pixel 4’s bezels are not a major crime against smartphone design, Andy Boxall discussed why having bezels is not an issue and the dislike for bezels is largely irrational.

Beyond aesthetics, there are drawbacks to using a device with thin or no bezels.

I can’t tell how many times I inadvertently touched unwanted user interface elements of apps on my old Pixel 2 XL phone and my current Pixel 4 XL, which have some bezel. For example when I grab the device ringing for an incoming call, which often results in a declined call because I touch the wrong areas close to the edges of the screen.

Bezels actually have advantages as they can accommodate the parts screen notches and holes house, such as cameras and sensors.

I use only Google phones, despise screen notches and holes, and wish Google focused on substantial features such as improving optical zoom (Super Res Zoom doesn’t qualify) rather than chasing questionable design decisions and fads with collateral damage like missing bezels.

The Pixel 4 XL was Google's last phone with bezels and no screen mutilations. What I hoped was a fad turned into a design trend and later Pixels came with screen holes.

My Pixel 4 XL is close to the end of life and I need to replace it with the upcoming Pixel 7 Pro. Guess what? It has a screen hole, I'll have to deal with it and get the device anyway.

Stop mutilating screens. I want my bezels back.

#Android

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I couldn't resist. I ordered an assembled V20-MBC Black Edition kit with 1 MB RAM, a homebrew computer by the same prolific maker of the Z80-MBC2. The devices share the same design, except instead of a Z80 like the Z80-MBC2 the V20-MBC features a Nec V20 bundling the 8088 and 8080 CPUs.

It's exactly what I needed, the perfect match for running my Assembly code on actual hardware and a complement to the Z80-MBC2.

Suite8080, my suite of Intel 8080 Assembly cross-development tools, includes the assembler I use for my 8080 programs executed on the Z80-MBC2 under CP/M-80, and now also on the V20-MBC as native 8080 code. I also set up an x86 Assembly cross-development environment to create 8086 code that will run on the V20-MBC under CP/M-86. And, of course, the Z80-MBC2 lets me run Z80-specific projects.

The shipping is on its way to me, I'll share my experience with the V20-MBC.

#v20mbc #retrocomputing #sbc #x86

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The Z80-MBC2 homebrew Z80 computer is a living retrocomputing museum that runs early microcomputer operating systems such as CP/M, QP/M, and UCSD p-System. Since the latter is the one I know least, I explore it with the Z80-MBC2.

On UCSD p-System the user runs programs and manages the system through a series of hierarchical menus, unlike the command interpreters of other operating systems. Navigating the menus down the hierarchy is easy, but sometimes I'm not sure how to get up one level. Pressing the Q key works most of the times, but occasionally nothing happens and I get stuck.

Running UCSD p-System gives a sense of how slow the output is on serial terminals. For example, a demo program to plot an ASCII sine wave takes almost 20 seconds over a 115200 bps serial line to the 8 MHz Z80-MBC2.

It's best demonstrated by a screencast I recorded, which shows the output as well as the menus. In the video the Z80-MBC2 runs in a Minicom terminal emulator session under Crostini Linux on my Chromebox.

#z80mbc2 #retrocomputing #sbc

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I don’t like algorithms deciding what ends up in my reading feed. For my content consumption I want platforms that don't filter but deliver all the content from all the sources I want, and only those sources.

This is why my information hub is an RSS feed reader, Feedly. In addition, since running my own email newsletter for some time, I have been subscribing to a growing number of newsletters on a variety of topics. From technology and software development, to content creation and publishing.

Here are the newsletters I subscribe to. I prefer niche, obscure, or unique sources, so I hope this list will help you discover valuable content that’s not mainstream.

I'll keep the list up to date.

#newsletters

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I cross-develop CP/M programs on Linux with the Suite8080 assembler and run them on a number of platforms, from software emulators to the Z80-MBC2 computer. But to test the code I use an emulator for Linux called ANSI CP/M Emulator and disk image tool, or just CPM.

CPM is unique in that it reduces development and testing friction. The emulator can execute CP/M programs stored on the Linux file system by passing CP/M executable files as arguments, such as:

$ cpm cpmprog

where cpm is the emulator and cpmprog.com is a .COM file on Linux. In addition, the current Linux directory appears as the A: drive from CP/M, so any .COM files there on Linux can be executed from CP/M like this:

A>cpmprog

Again, cpmprog.com is a .COM file on Linux.

This feature shortens the development cycle, as the emulator can access program files cross-assembled on the same file system it runs on.

Other emulators require copying files to disk images and mounting the images from the emulated environment. And before they can be run on the Z80-MBC2 or other hardware, CP/M programs need to be transferred via XMODEM or other means.

Once a .COM program is tested and debugged, I run it on richer CP/M environments like the z80pack emulator or the Z80-MBC2.

#retrocomputing #cpm

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