My old Space Invaders game running on an arcade cabinet!

A few years back, Color Computer community member Rietveld Rietveld took an Arcade1Up Rampage cabinet and converted it so I could run other software — such as emulators. Images have been shown of it running the Color Computer emulator and software.

Now, with the official 1.0 release of the NitrOS9 “Ease of Use”, that has been installed on this arcade machine and, by request, my OS-9 game Invaders09 has been ran on it.

I never imagined that my “arcade” game would eventually be running on a (sorta) arcade machine. Thanks, Rietveld!

Reversing bits in C

In my day job, we have a device that needs data sent to it with the bits reversed. For example, if we were sending an 8-bit value of 128, that bit pattern is 10000000. The device expects the high bit first so we’d send it 00000001.

In one system, we do an 8-bit bit reversal using a lookup table. I suppose that one needed it to be really fast.

In another (using a faster PIC24 chip with more RAM, flash and CPU speed), we do it with a simple C routine that was easy to understand.

I suppose this breaks down to four main approaches to take:

  • Smallest Code Size – for when ROM/flash is at a premium, even if the code is a confusingf mess.
  • Smallest Memory Usage – for when RAM is at a premium, even if the code is a confusing mess.
  • Fastest – for when speed is the most important thing, even if the code is a confusing mess.
  • Clean Code – easiest to understand and maintain, for when you don’t want code to be a confusing mess.

In our system, which is made up of multiple independent boards with their own CPUs and firmware, we do indeed have some places where code size is most important (because we are out of room), and other places where speed is most important.

When I noticed we did it two different ways, I wondered if there might be even more approaches we could consider.

I did a quick search on “fastest way to reverse bits in C” and found a variety of resources, and wanted to point out this fun one:

At that section of this lengthy article are a number of methods to reverse bits. Two of them make use of systems that support 64-bit math and do it with just one line of C code (though I honestly have no understanding of how they work).

Just in case you ever need to do this, I hope this pointer is useful to you.

Happy reading!

ChatGPT AI can analyze 6809 assembly language!

I gave it this:

    lda #96
    ldx #1024
    sta ,x+
    cmpx #1536
    bne loop

…and ChatGPT gave me this:

The clear subroutine in this code is used to clear the screen and initialize it with a grid of green squares. The subroutine begins by loading the value 96 into the accumulator register A using the LDA instruction. This value represents the color value for green, which will be used to fill the screen with green squares.

Next, the LDX instruction is used to load the value 1024 into the X register. This value is the memory address of the top left corner of the screen, and it will be used as the starting point for the POKE operations that will be used to fill the screen with green squares.

The loop label marks the start of a loop that will be used to fill the screen with green squares. Inside the loop, the STA ,X+ instruction is used to store the value in the accumulator register A at the memory location pointed to by the X register, and then increment the X register by one. This has the effect of setting the value at the current memory location to the color value for green, and then moving to the next memory location on the screen.

The CMPX instruction is then used to compare the value in the X register to the value 1536. If the X register is less than 1536, it means that there are still memory locations on the screen that need to be filled with the color value for green. In this case, the BNE instruction is used to branch to the loop label, causing the loop to be repeated and the next memory location on the screen to be filled with the color value for green.

If the X register is equal to 1536, it means that all of the memory locations on the screen have been filled with the color value for green, and the loop can be exited. In this case, the BNE instruction will not be executed, and the RTS instruction will be executed, causing the subroutine to return to the main program. This completes the execution of the clear subroutine.

– ChatGPT AI

Now, it may have figured some of this out because I previously fed it a longer (and fully commented) bit of 6809 code that contained that routine as one of its several functions. That’s the only way I can see it knew the screen location and a green block., ya’ll.

My 1987 Paper Route program I wrote for Laverne Ricks in Lufkin, Texas

Recently on LinkedIn, I saw a post by Rogelio Perea about his Tandy Model 102 portable computer. Although I never owned one, I remember this machine well. I always wanted one. Having a “portable” computer really wasn’t a thing back in those days, and this one even had a modem built in!

I recalled how, when I worked for Radio Shack, I wrote a program on our display Model 102 that we used to track our customer repairs. We had to have everything on paper in those days, but would type things in to the computer so we could find them quicker when a customer inquired about their repair status. I wish I had a copy, but I think the only place it ever existed was the memory of that specific computer.

I do, however, have the program it was based on. It started out as a PEN-PAL program for the Radio Shack Color Computer:

This program, in turn, was based on work I had done for my *ALL RAM* cassette-based BBS program.

*ALLRAM* used BASIC arrays to store the userlog and message base in memory, and would load/save them to tape. My Pen-Pal program did the same thing, but was updated to load from either Tape or Disk.

That Pen-Pal program was also the basis for a custom program I wrote for a lady who ran a large newspaper route where I lived at the time. Her name was Laverne Ricks, and I remember this because I put it on the title screen of the program I wrote for her:

According to comments in the source code, I wrote this on 7/8/1987. This was the summer after I graduated high school, and I had just moved to Lufkin, Texas. Since this was before I got a job at Radio Shack, I am not sure how she and I got connected (possibly through the Lufkin Area CoCo Club or someone at Radio Shack).

The initial version of the program has a menu very similar to the Pen-Pal program:

You can see I had made it look a bit nicer by using graphical black block characters instead of rows of equal signs ;-)

I also found a second version, where I added built-in help:

THIS must be why I wrote the BASIC windowing routine I have written about before. It offered several screens of help:


The program has ways to Add a new record:

Ah, the days before spell checkers. You should see the misspellings in my furniture store inventory program I did a year or so later… But I digress.

And you could use arrow keys to flip through them:


You could Delete entries, Edit them, and Insert new ones (at the location you were currently viewing, which was important since a Paper Route was organized by delivery location rather than alphabetical or whatever). There was a way to Jump to a specific entry as well.

And, of course, you could Search by field:

Looking at it 35 years later, I’m pretty impressed with the features it offered. I have no idea what I based all of this on since I’d only owned a VIC-20 and a CoCo at that point and certainly had never worked with any kind of database software that I can recall.

Side note: A short while later, I would do something like this again for someone who ran a garbage collection route, though I think it was for a Tandy 1000 and was using a Deskmate Database.

This is what let me to search out Laverne Ricks and see where she was these days. Sadly, she passed away in 2011.

Rest in peace, Laverne Ricks. A tiny bit of your legacy will be remembered here, always.

Until next time…

Insat360 X3 now allows changing WiFi password

The Insta360 app has an option to change the password on the X3 camera. This may also work on other cameras, but I have not tested it. I have done a password change, but have not verified this actually did anything.

This option will cause the camera to display an authorization prompt, and once confirmed, you can type in a new WiFi password which the device will use.

I encourage ALL Insta360 camera owners to do this, as the default password is well documented and it allows anyone within WiFi range to access and download any photos/videos on the camera.

Arduino, ZigBee and motion sensor help needed.

For a future project, I need to make use of remote triggers. These could be motion sensors, beam sensors, pressure mats, etc.

The ZigBee standard seems to be the way to go since I can find cheap consumer motion sensors that run on batteries. There also seems to be ZigBee repeaters, which allow giving the distance I need simply by plugging them in from place to place to create a mesh network.

XBee might be another option, if cheap motion sensors and repeaters are also available.

The goal is to have a central location be able to read the motion sensor status for many sensors, that could be spread out beyond walls hundreds of feet away.

Any pointers to where I might get started would be appreciated. Ideally I’d drive this all by a low-cost Arduino since the device will be used in an area where power might not be stable (and I wouldn’t want to corrupt the Linux file system on a Raspberry Pi).


Carl England must be stopped.

Earlier this month, I received a message on my Sub-Etha Software Facebook page from author (and former/current CoCo programmer) Carl England:

I knew CHR$(13) was a carriage return, so this was creating a file name that contained carraige returns. What would that do?

I typed it in to find out…

How appropriate, because the first thing I said when i saw this code was “weird.”

Of course, now I have a file on my disk that would be hard to delete. Carl said just doing:


…would take care of it. Provided, of course, you did that after running the program, while A$ still existed. Otherwise you’d have to manually type that line again and replace the SAVE with KILL.


Character 8 is a backspace, so I could sorta see what this was doing. “TEST” then four backspaces, then a period, then three more backspaces?


Also weird.

I could have had so much fun with this trick back when I was swapping disks with friends.

Thanks, Carl!

Exploring 1984 OS-9 on a 64K TRS-80 Color Computer – part 3

See also: part 1, part 2 and part 3.

Welcome back to the days when an IBM Compatible PC required a floppy disk just to start up. You would boot to PC-DOS (on an actual I.B.M. machine) or MS-DOS (for a clone, like the Tandy 1000 that had just come out in 1984 as the first PC compatible for under $1000). And … then what?

Just like there wasn’t much you could do with a PC with only a DOS boot disk, having just OS-9 is rather limited as well. Beyond typing some commands, what could you do?

There was a simple line-based text editor that would let you make text files. You could then “list” the text file and have that redirected to a printer, if you had one.

I guess you could say this was very limited word processing. Just without much word processing (though the EDIT command has search and replace functions).

There was also a 6809 assembler and debugger. You could write programs in 6809 assembly language.

And that was the very first time I ever wrote an OS-9 Level 1 assembly language program, and also the first time I ever used the asm assembler. I was more familiar with the rma assembler that came out for OS-9 Level 2 on the CoCo 3.

What else? Well, just like DOS, if you wanted to do more, you’d need software. Initially, Radio Shack didn’t sell anything for OS-9 other than BASIC09. Investing in that would allow someone who knew normal BASIC to start writing programs for OS-9. (I plan to do a “Converting Color BASIC to BASIC09” series at some point.)

But it was still neat.


Multi-user support is great, but if you only have one keyboard it won’t get you very far. But, OS-9 came with drivers for the CoCo’s banger RS-232 port, and also a “time sharing monitor” program that could monitor such serial port and then launch the “login” program if a terminal was hooked up to such serial port.

You could plug up an RS232 terminal to the CoCo’s serial port, and then launch “tsmon /t1 &” (the ampersand made the program run in the background so the shell prompt would return immediately). Now both you at the keyboard and another user via the serial port could be using the system at the same time. (Albeit at 300 baud.)


If that terminal was another CoCo, then a remote login might look like this:

Above, I added a new entry to the PASSWD file for “ALLEN” with a password, and made new directories /D0/USERS/ALLEN. I set that login entry to point to that directory so when I logged in, I would have been changed in to /d0/USERS/ALLEN ready to make new files there.

It’s a bit more work than this to be useful, but that’s basically the idea. It was really a game changer compared to using BASIC in ROM.


So what could you do with this 1984 OS-9 Level 1? Write programs in assembly, or buy BASIC09 and write programs in that langauge.

However, since text-based OS-9 applications were compatible across hardware, there were actually existing OS-9/6809 programs that could run on the CoCo. Third party software specifically for CoCo OS-9 would soon follow, which was interesting because CoCo OS-9 could do graphics.

But that’s an article for another day.

Until next time…

Exploring 1984 OS-9 on a 64K TRS-80 Color Computer – part 2

See also: part 1, part 2 and part 3.

Obtaining a Time Machine

Since most of us will not have a 64K Radio Shack TRS-80 Color Computer laying around, as well as a disk drive and the original OS-9 floppy disks, I suppose running an emulator on your PC/Mac/Linux machine will have to suffice.

I personally use the XRoar emulator since I can run it on my Mac, Windows PC or Raspberry Pi. It allows me to emulate everything from a 1980 4K CoCo with Color BASIC 1.0, on up to a 512k CoCo 3. It has been invaluable in articles I have written, because I can quickly switch between Color, Extended and Disk BASIC systems of various versions using various amounts of RAM. There are other options available such as VCC for Windows, or the cross-platform MAME, but I do not know the specifics of how (or if) they can emulate an old 64K CoCo. (I think VCC is CoCo 3 only.)

Over at the Color Computer Archive, disk images have been preserved from the original V1.00.00 release of CoCo OS-9:

I went and found the very first V1.00.00 release:

OS-9 Level 1 v01.00.00 (Tandy) (OS-9).zip

There was a later V1.01.00 update, and then an even later V2.00.00 update, but I want just just focus on what 1984 had to offer.

Inside that .zip file you will find two disk images:

  • OS9L1V1B.DSK – boot program (for Disk BASIC 1.0 users) and disk drive speed test utility.
  • OS9L1V1M.DSK – the actual OS-9 operating system itself, contained on this 156K 35-track single sided disk image.

As long as your CoCo or emulator is set to have 64K and Disk Extended Color BASIC 1.1, you can just mount the second one (OS9L1V1M.DSK) and then type “DOS” to boot in to OS-9. It will take awhile, since we are also emulating a slow floppy drive.

OS-9 Level 1 on a 64K Radio Shack TRS-80 Color Computer (emulated).

A “set time” utility is there asking for date and time — anyone here old enough to remember with early PCs all did the same thing as they booted to PC-DOS? Life before realtime clocks – the struggle was real!

Sadly, the set time utility is not Y2K compliant and will not let you enter “22” to mean 2022. You can type something like “22/7/27 8:58” but it will treat that as the year 1922.

22 means 1922. Sorry, folks living in 2022.

I should point out that, internally, it seems the clock code understood years past 2000 — but the utility did not allow you to enter them. If you set the time to just before midnight on December 31, 1999, then wait, you will see it rolls over from 1999 to the year of 19100:

From 1999 to 19100 in ten seconds flat!

The NitrOS9 project, which has created an open source update from the old OS-9, has fixed all these issues. Anyone interested in running OS-9 on a CoCo these days should be using that, but for this article, we will be sticking strictly with stock OS-9 as it existed in 1984. Which means maybe I should have entered the year to be 1984…

But I digress…

OS-9 Beginner’s Guide

I used to teach week-long courses on OS-9 for Microware, but we’ll keep this article much simpler and just look at commands and how the disk directories are set up.

As mentioned earlier, there is a “set time” utility, and in the previous screen shot you can see I used a command called “date” which will display the date. Typing it with the option of “t” added — “date t” — will display the date and add the time at the end.

If you type “dir” you will get a directory of the OS-9 disk:


 DIRECTORY OF .  00:05:38

Unlike Disk BASIC, OS-9 has a real file system that support longer filenames, upper and lowercase, subdirectories and much more. Since the CoCo VDG chip lacked true lowercase characters (lowercase existed, but would be displayed as inverted uppercase characters), by default CoCo OS-9 displays everything in uppercase even if the underlying text is using lowercase. You can type commands in upper or lowercase since the file system is not case sensative.

We see five filenames, but can’t tell if they are files or directories. There is a convention in OS-9 to make filenames lowercase, and directory names UPPERCASE. Since we can’t see the difference, we can use the option “e” on the dir command to display a longer listing:


 DIRECTORY OF . 00:08:28
83/06/02 1921   0  OS9BOOT
------WR       A     3032
83/06/02 1956   0  CMDS
D-EWREWR      3C      620
83/06/02 2002   0  SYS
D-EWREWR     164       A0
83/06/02 2002   0  DEFS
D-EWREWR     17F       C0
83/06/02 2003   0  STARTUP
----R-WR     15F        E

Yuck! But we’ll get to what this means in a moment. You will see the screen pauses at the end. This is a feature built-in to OS-9 and it can be turned on or off. Press SPACE and you will see the listing continues, but there wasn’t anything left other than an empty line before returning to the “OS9:” command prompt.

Looking at that listing, if we made it expand to a wider display, it becomes much easier to understand. It might look like this on a 40 or 80 column OS-9 system:

 DIRECTORY OF . 00:08:28
83/06/02 1921   0  OS9BOOT  ------WR       A     3032
83/06/02 1956   0  CMDS     D-EWREWR      3C      620
83/06/02 2002   0  SYS      D-EWREWR     164       A0
83/06/02 2002   0  DEFS     D-EWREWR     17F       C0
83/06/02 2003   0  STARTUP  ----R-WR     15F        E
  • CREATED ON – The first column is the date (YY/MM/DD) and time (HHMM) the file/directory was created.
  • OWNER – The second column is the owner of the file/directory. OS-9 Level 1 is a multi-user system, and each user can have its own unique user number. 0 is reserved for the administrator (super user).
  • NAME – The third column is the file/directory name. OS-9 Level 1 allowed filenames to be up to 28 characters long, and use upper and lowercase. Spaces are not allowed, and there are some other restrictions, like files cannot start with a number and most special characters are not allowed. But still, far more advanced than DOS was.
  • ATTR – Attributes of the file. This is how we can tell if something is a file or a directory. There are eight attributes, and the first is D if it is a directory, or – if it is a file. We can skip the next one, and focus on the next two sets of 3 attributes. They are “EWR” — the first three are PUBLIC Execution (for binaries), Write (writeable), and Read (readable). The next three are the same but for the OWNER. Thus, you can have a file that ONLY the user can read, or everyone can read. You can make a file that only the user can write to, but the public can read but NOT write to. The same thing for directories. Private directories could exist, usable only by the owner, or public, that other users on the system could read and/or write to.
  • START – This is a hexadecimal value of what logical sector the file/directory starts at on the disk system. OS-9 splits a disk up in to logical sectors of 256-bytes each. We don’t need to worry about this.
  • SIZE – This is the file size, also shown in hexadecimal. We see the “startup” file is E (&HE to BASIC users, or 0xE to C programmers) long – 14 bytes.

Here are what those files are:

  • OS9BOOT – The OS-9 boot file, which contains the kernel, device drivers, etc. This will be all the files necessary to get the system up and running to the OS9: command prompt.
  • CMDS – We see that this is a directory. It contains various command line utility programs.
  • SYS – Another directory. This one contains system text files.
  • DEFS – Another directory. This one has definition text files used by the assembler/compiler and such.
  • STARTUP – This is a text file with public Read and owner Write/Read. It is basically AUTOEXEC.BAT for OS-9.

Let’s try the “list” command on the STARTUP file, which we know is 14 bytes long:


The contents of the file is displayed, much like using “cat” under Linux or “type” under MS-DOS. We see the contents is one line, “SETIME </TERM” and if we counted those characters, we’d get 13 characters. The file size is 14, because it contains those thirteen characters plus a carriage return at the end of the line.

By default, OS-9 will boot and then run whatever is in this STARTUP file. This allows us to customize things if we wanted to, or remove that set time prompt completely.

Let’s see what is in the various directories.



ASM       ATTR      BACKUP
PROCS     PWD       PXD

There is quite a bit available! We see some commands that may look familiar — like DATE (show the date), DEL (delete a file), COPY (copy a file), DIR (directory), DELDIR (delete directory), ECHO (echo text), LIST (list a file), MAKDIR (make directory), RENAME (rename a file) and so on. OS-9 has a full file system with most of the standard commands you would expect.

If you have ever used “CHKDSK” on a PC or “fsck” on Linux, you will find OS-9 DCHECK familiar. If you have ever merged files on a Linux system, MERGE will be familiar.

OS-9 is very Unix-like in design, and with Linux being based on UNIX, it will have some familiar aspects to a Linux user.

We will explore these commands later, but let’s keep looking.




Not much there. All three of these are text files.

  • ERRMSG – Contains a text listing of error messages (OS-9 will use an error number like ERROR #216, and this text file will show you that it means “PATH NAME NOT FOUND”.) You could type “LIST SYS/ERRMSG” if you wanted to see them all. You can also type the command PRINTERR to activate long error messages. Now instead of just getting “ERROR #216” it will be followed by the text description from the file. This will make error messages slower, though, since each time it will have to seek through the text file to find the entry and display it.
  • PASSWORD – As a multi-user system, OS-9 has a password file that can have entries for each user. You could create a password file with an entry for “admin” that would let them log in, change to the user’s “home” directory, and set their user ID to 0 (super user). Or you could make an entry for “bob” that sets his home directory somewhere else and makes him user 42, non-super user. Type “LIST SYS/PASSWORD” to see what is in there. You will see nothing is encrypted. Ah, those early days of operating systems! This file is used by the “login” command.
  • MOTD – Message of the Day text file. This file will be displayed to a user after they log in using the login command. We don’t see it because by default this OS-9 just boots directly to an OS9: command prompt.




There are text files used by the 6809 assembler. They are sorta like .h header files in C. They contain various text definitions for bit values or whatever.

  • OS9DEFS – Definitions for the operating system.
  • RBFDEFS – Definitions for the “random block file” manager (disk).
  • SCFDEFS – Definitions for the “sequential character file” manager (console, serial ports, etc.)
  • SYSTYPE – Definitions for the system.

Unless we are programming for those, we would never use these files.

So what can we do?

In the next installment, we’ll explore some of the commands, and discuss some of the things that make OS-9 very unique (and the reason why it can run as a disk-based operating system, or completely out of ROM with no file system at all).

To be continued…