Paolo Amoroso's Journal

It's been over a week since I received the Z80-MBC2 Z80 single-board computer, so I got a chance to spent some time exploring and playing with it. Although I shared some usage updates, it's time for some notes on how the board is working, its value and potential, and the issues I'm facing.

I wish to thank the board's developer and the retailer I bought it from, who clarified some features and details.

Hardware

The Z80-MBC2 comes with two additional small cards (a microSD reader and a real-time clock unit) and a USB serial adapter to plug into the main board. It was easy even for someone with no hardware skills like me, but I had to check some product photos and seek help to figure how to match the connectors.

Here is the board with all the parts plugged in.

What surpised me about the Z80-MBC2 is its heft compared with the small size. It weighs almost as much as a smartphone, as those old-fashioned chips pack a lot of stuff.

At 10x10 cm, the Z80-MBC2 is compact and fits well next to my Chromebox as this photo shows. Via the USB serial cable, long enough for my setup, I plug the unit into the Chromebox and access it via the Minicom terminal emulator.

I haven't perceived any significant warming of the board after prolonged use. The readings of the built-in temperature sensor usually stick around 32-33° C.

Software

The Z80-MBC2 is a great kit aimed at hobbysts and electronic enthusiasts, but no mnual is available. There's little documentation on how to operate the product and what it can do.

However, some background on computer technology, programming languages, and 1980s 8-bit systems make it easy to learn by experimenting and interacting with the board. The Z80-MBC2 project site, as well as the site of the predecessor Z80-MBC, are useful sources on the features and capabilities of the product.

The firmware comes with lots of software and tools, see this screenshot of the boot menu. There are programming language interpreters like on 1980s microcomputers, such as BASIC and Forth, and a number of operating systems like CP/M 2.2 and 3.0.

The firmware provides an option for uploading an executable file in Intel HEX format. For example, this allows experimenting with software designed to run on the bare metal such as resident monitors or other low-level code.

Value and potential

I bought a professionally assembled and tested Z80-MBC2 unit. The main value of this solution is the product is pretty much plug and play.

It comes with everything needed to start using the board. In particular, the latest version of the firmware, which fixes some I/O issues, and the USB serial adapter. All I have to do is plug the board's USB connector into a port of my Chromebox.

The board is perfect for running my Assembly code on actual hardware.

The Z80-MBC2 is also an interactive history of computing lab, a way of feeling first-hand the performance and latency of early 8-bit microcomputers and I/O. I actually experienced that kind of performance back in the day but lost touch with it long ago.

Issues

I love the Z80-MBC2 but an issue is limiting what I can do with it: XMODEM file transfers from Crostini Linux to the board time out. Given XMODEM is the most effective way of sending code and programs to the board, this is a major inconvenience.

I'm troubleshooting the issue with the help of comp.os.cpm. The Z80-MBC2 developer reassured me it's likely not a firmware problem, as versions earlier than the one I have didn't fully support XMODEM.

Meanwhile, I'm looking for workarounds shouldn't I be able to devise a fix.

For example, I could paste a file from the terminal emulator to a text editor running on the board. Another less practical option would be to copy the files on the microSD card, the mass storage device of the Z80 system.

#z80mbc2 #sbc #CPM

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Back in the CP/M and MS-DOS days, developers shipped software with all sorts of device drivers to support such basic peripherals and system services as terminals, graphics cards, mices and input devices, memory management, mass storage units, printers, network equipment, and more.

Every developer pretty much had to reinvent the wheel. Yet the industry thrived, and many software houses and independent programmers published successful applications and games.

These days mobile developers gripe about Android fragmentation, a consequence of the success of open platforms like CP/M and the IBM PC.

#Android #development #retrocomputing

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When I decide to buy a tech product or gadget, I know how to use it even before ordering or ever having held it in my hands.

How? As a side effect of researching the product.

To learn more, I download the manual or visit the documentation website and read it in full. Reviews, unboxing videos on YouTube, blog posts, and Reddit discussions are other valuable sources of information and tips.

By the time the product is in my hands, I know how to operate and find my way around it. Reading the manual also gives a heads up on any required setup steps, data I need to gather, decisions to make, handling precautions, usage quirks, and useful features.

This knowledge saves time when I want to get up to speed with a new gadget.

#misc

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In the Crostini Linux Minicom terminal emulation session of this screenshot, a hello world Intel 8080 Assembly program run under CP/M on the Z80-MBC2 Z80 homebrew computer, printing the string Greetings from Suite8080 to the console.

It may not seem like much, but it's a personal achievement I'm proud of.

The demo program comes with Suite8080, a suite of Intel 8080 Assembly cross-development tools I'm writing in Python. I created the demo, assembled it with my own assembler, and run it on actual hardware. Just a few months ago I didn't think I could do this.

Running the demo also helped me put together and test a cross-development toolchain based on Suite8080. For example, I learnt how to transfer files via XMODEM from Crostini to the Z80 board.

I can't wait to use the toolchain to develop more code for the Z80-MBC2.

#Suite8080 #z80mbc2 #sbc #CPM

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It turns out the Z80-MBC2 Z80 homebrew computer does work with chromeOS. This screenshot of a Minicom session under Crostini Linux shows CP/M 3.0 booting up on the Z80 board.

It took some troubleshooting of the connection between the Z80-MBC2 and my Chromebox to make chromeOS detect the board. How?

I just re-plugged the board's USB cable into the Chromebox.

The idea came as a result of asking for help on r/chromeos. A redditor noted connecting a USB serial device to a chromeOS machine is a bit hit and miss, i.e. some attempts to connect may not be successful.

This prompted me to re-plug the Z80-MBC2, and chromeOS popped up a notification to let me share the detected USB device with Crostini. It's been working consistently since then.

Interestingly, the board is supported only under Crostini but not in the Android container or the web subsystem of chromeOS, as the Serial USB Terminal Android app and the web apps based on the USB Web Serial API still don't detect the Z80-MBC2.

I can finally dive into and play with this awesome gadget. Fun ahead!

#z80mbc2 #sbc

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The Z80-MBC2 board, a Z80 homebrew computer I ordered, finally arrived and I connected it via serial USB to my i7 ASUS Chromebox 3, hoping to control the board from a terminal emulator.

I got a professionally assembled and tested Z80-MBC2 unit and the developer confirmed I hooked it up correctly, so I'm confident the hardware is working. All the right leds are on, as shows this photo of the board connected to the Chromebox at right (the “Z80 inside” logo alone is worth the board).

However, the Chromebox doesn't recognize the board neither under Crostini, nor Android, nor chromeOS.

In Crostini, the output of lsusb doesn't list the board:

Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

The output of usb-devices doesn't list it either:

T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=480 MxCh= 8
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0002 Rev=05.10
S:  Manufacturer=Linux 5.10.110-15808-ge5740beba59b xhci-hcd
S:  Product=xHCI Host Controller
S:  SerialNumber=0000:00:0c.0
C:  #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=0mA
I:  If#=0x0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub

T:  Bus=02 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=5000 MxCh= 8
D:  Ver= 3.00 Cls=09(hub  ) Sub=00 Prot=03 MxPS= 9 #Cfgs=  1
P:  Vendor=1d6b ProdID=0003 Rev=05.10
S:  Manufacturer=Linux 5.10.110-15808-ge5740beba59b xhci-hcd
S:  Product=xHCI Host Controller
S:  SerialNumber=0000:00:0c.0
C:  #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=0mA
I:  If#=0x0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub

There's no entry related to the Z80-MBC2 in the output of ls -l /dev:

total 0
drwxr-xr-x 3 root   root          60 Jun 16 12:30 bus
crw--w---- 1 root   tty     136,   0 Jun 16 12:30 console
lrwxrwxrwx 1 root   root          11 Jun 16 12:30 core -> /proc/kcore
drwxr-xr-x 2 root   root          80 Jun 16 12:30 dri
lrwxrwxrwx 1 root   root          13 Jun 16 12:30 fd -> /proc/self/fd
crw-rw-rw- 1 nobody nogroup   1,   7 Jun 16 12:30 full
crw-rw-rw- 1 root   root     10, 229 Jun 16 12:30 fuse
lrwxrwxrwx 1 root   root          12 Jun 16 12:30 initctl -> /run/initctl
crw-rw---- 1 root   kvm      10, 232 Jun 16 12:30 kvm
lrwxrwxrwx 1 root   root          28 Jun 16 12:30 log -> /run/systemd/journal/dev-log
drwxr-xr-x 2 nobody nogroup       60 Jun 16 12:30 lxd
drwxrwxrwt 2 nobody nogroup       40 Jun 16 12:30 mqueue
drwxr-xr-x 2 root   root          60 Jun 16 12:30 net
crw-rw-rw- 1 nobody nogroup   1,   3 Jun 16 12:30 null
crw-rw-rw- 1 root   root      5,   2 Jun 16 12:43 ptmx
drwxr-xr-x 2 root   root           0 Jun 16 12:30 pts
crw-rw-rw- 1 nobody nogroup   1,   8 Jun 16 12:30 random
drwxrwxrwt 2 root   root          40 Jun 16 12:30 shm
drwxr-xr-x 2 root   root         140 Jun 16 12:30 snd
lrwxrwxrwx 1 root   root          15 Jun 16 12:30 stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root   root          15 Jun 16 12:30 stdin -> /proc/self/fd/0
lrwxrwxrwx 1 root   root          15 Jun 16 12:30 stdout -> /proc/self/fd/1
crw-rw-rw- 1 nobody nogroup   5,   0 Jun 16 12:30 tty
crw-rw-rw- 1 nobody nogroup   1,   9 Jun 16 12:30 urandom
crw-rw-rw- 1 root   root    245,   0 Jun 16 12:30 wl0
crw-rw-rw- 1 nobody nogroup   1,   5 Jun 16 12:30 zero

In the Android contanier I use the Serial USB Terminal terminal emulator app, but the Z80-MBC2 doesn't show up in its list of USB devices.

Finally, on chromeOS I use a few terminal emulator web apps based on the USB Web Serial API, such as this one. Again, there's no Z80-MBC2 entry in the app's list of USB devices.

I connected the Z80 board also to my Lenovo Yoga N26 Chromebook. Same result under chromeOS and Android, i.e. the device isn't detected. I don't use Crostini on the Chromebook.

I have a couple more things to try, but I suspect chromeOS doesn't support the board's serial adapter.

I knew USB is chromeOS' Achille's heel. But, although I expected USB issues with Crostini because of its heavily sandboxed environment, what suprised me is the Z80-MBC2 is not detected by chromeOS or the Android container, which may have fewer USB restrictions and wider support.

#z80mbc2 #sbc #CPM

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Simon Wilson celebrated 20 years of blogging by featuring his most influential posts, describing his publishing platforms and tools, and discussing the evolution of his blog's design. Simon's software development career is equally impressive as he was a co-creator of the Django Python web framework.

#blogging

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I'm about to resume working on my Suite8080 project after putting it aside for a few months. And I bought a Z80 homebrew computer.

To refresh my 8080 Assembly to work on the Suite8080 code, and my Z80 to play with the new computer, I'm rereading the book Z-80 and 8080 Assembly Language Programming by Kathe Spracklen (Hayden Books, 1979).

It's a short, clear resource that includes several worked out exercises. It presents and compares the code samples and concepts in both instruction sets. The book also covers how to implement basic data structures in Assembly, which makes it stand out.

#Assembly #intel8080 #z80 #books

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While I decide what to do with my old blog, I turned off commenting. I have always moderated comments and never let any junk show up, but these days the volume of comment spam is annoying enough to no longer justify the effort. Besides, socials killed blog commenting anyway and I haven't been getting any legitimate ones for years.

#blogging

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8bitnews is a newsletter curating and handpicking retrocomputing content. I read it cover to cover and don't miss an issue.

The newsletter covers retrocomputing news and projects with quality curation, a wide variety of resources, and a distinctive upbeat voice. I particularly like 8bitnews for its wide scope. While many retrocomputing blogs and publications focus on gaming, 8bitnews shares also content about vintage-related technologies, devices, software, and programming.

#retrocomputing #newsletters

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