Dunfield 6809 Portable
dunfield.classiccmp.org
dunfield.classiccmp.org
Multiple stack registers for complex argument passing.
Internal 16-bit registers.
(Integer) Multiply/Divide.
Sign extension (SEX instruction!)
Years later I did some embedded OS/9 (Not the Apple OS, but the Microware one.) The target was actually a 68k, but the OS had been ported from the original 6809 platform. It was pretty powerful for the day and although not completely POSIX compliant, it was very POSIX-like.
I haven't tried his CUBIX on his emulator yet, but there's a certain richness to systems that start with a full fledged debugger on the bare metal. And he's got his own assembler, Forth, BASIC, APL, C compiler...
What does this mean? Aren’t all registers (for any mainstream processor) internal?
https://www.amazon.com/MOTOROLA-MC6809E-MICROPROCESSOR-PROGR...
For a small town kid interested in all this stuff, that made quite an impression. Instant Moto fan.
My co-workers went nuts with the PC-relative capabilities, but I didn't bother- those addressing modes were pretty slow.
We had a cool piece of hardware: an in-circuit emulator. The 6809 version of this one:
http://www.decadecounter.com/vta/articleview.php?item=1064
That thing was the bomb, because it had trace memory so you could watch what led up to an interrupt causing your system to crash. Non-symbolic though, you needed the linker map and assembly listings by your side to do anything.
http://www.iobium.com/applied_microsystems_em189_e.htm
$3750 in 1983.. $10,106 in today's money..
I got into broadcast character generators in 1989. Mind telling me who you worked for, and what you worked on?
Oh, I bet you had this experience: 100s of monitors whining at near 15734 Hz, damaging your young ears..
Yeah, I've heard that whine. Haven't heard it in years, though. Both monitors and my ears have changed...
Did you ever go to the National Association of Broadcasters trade show? That was loud. Hundreds of monitors, but dozens of booths, each trying to play catchy audio loud to attract attention.
Prosumer and professional character generators are woefully underdocumented. Anyone wanna donate any old functional ones to me? I'll set up and make a Youtube series about them lol. I'd love to see them eventually be emulated in the way that classic game consoles and home computers have been.
I'm 40 years old and I can still hear flyback. I actually have a Roku Express+ hooked up to a 27" Trinitron. I miss the days of CRTs, except for their weight.
I miss CRT's too, and I have a couple. One, near my work desk, is a lightly used SONY PVM, high pitch Trinitron. I love to have movies playing on it when working. Above it, on a shelf, are a reasonable VHS that I use for capturing tapes and watching movies on as well as some not so special DVD/Blu-Ray player I should hook up via RGB, but is running S-video.
Rambling aside, I would enjoy a video series on character generators. Lots of us geeked out on broadcast details.
Personally, I would enjoy any tech info on how the characters were done and what trade-offs got made any why. Some of what was out there looked very good. Other gear, not so much. Bet it's a few minor details that differentiate those outcomes too.
We had descriptions of each character of each font in a scalable, vector form. To draw a character, we'd draw it as a bitmap (1-bit depth) at 4 times the size. Then we would shrink each 4x4 cell down to one 8-bit value (weighting the center more than the edges). That 8-bit value was the alpha (transparency) value for drawing the character over whatever was already there in the frame buffer.
When drawing (compositing) one thing over another with an alpha channel, we used true Porter & Duff compositing, with pre-multiplied colors. We had a custom ASIC that would do it, so it was fast.
One of the trade offs was the rise time (or number of pixels, same thing) of the edge of a character. Too fast and the NTSC video signal couldn't handle it (and you'd have visually obvious stair-steps on the diagonals). Too slow and the characters looked soft rather than crisp.
So the frame buffer was compressed using run-length coding. The hardware decoded it on the fly when generating the video. Anyway, we could get very high resolution this way with a tiny fast SRAM frame buffer, it looked great.
A problem was that even with the 68000, composing a page from text was quite slow: 10 seconds for single line, something like that.
One of the products was a teleprompter. To make smooth slow scrolling without complex sampling we moved the screen by changing the vertical sync position. This is not so easy to do well because the vertical sync detector in the monitor is pre-charged by the nearest horz sync (this is why NTSC has the double-rate serration pulses for interlace).
On the other hand, we did roll and crawl effects using fast 6809 assembly on other products. The font on this type was very crude- either fixed width characters like a terminal or semi-proportional spaced, where the width had to be a multiple of some number of pixels (so still character cells). You could get away with it on CATV bulletin board devices, but not in high quality titlers.
It also explains some of what we would see on various systems too.
If, say target frame buffer was some multiple of the color clock, it would be 320, 640, maybe as low as 160 pixels. (We had a couple of those and it was crappy obvious)
That ramp seems like it needs to align with that clock too, or there would be color fringing. Avoiding it entirely is gonna be soft, or strict limits on color combos.
(How many TV newscasts went with blue and white?)
Going sharper would mean a potential color artifact amd or different ones, depending on the alignment between the color clock and the ramp pixel start?
Say it was a blue fringe. Placing the glyph on an even pixel start might generate a bluish artifact, and a reddish one on an odd pixel. (Assuming 320 pixels for illustration)
Good placement against say a blue background, maybe gradient to also mask even odd line effects...
Were there placement limits per glyph to keep these things consistent? Did you guys get down to that detail?
Some of the graphics seen near the end of SD were sweet! Like almost every issue woven into a nice looking, very clever package.
As I remember it, it had the instruction MUL, which did 8 by 8 bit unsigned multiply, but no divide.
Maybe the Hitachi CMOS version had it? I know this version had undocumented additional instructions.
EDIT: WP says it had hardware division:
https://www.youtube.com/watch?v=Vsg97bxuJnc
"I have much more in this small CPU than great comfort at a most pleasant price. I have great confidence, for which there can be no price. In 6809, I have what I need."
I just got a nice, old CRT for use with my retro machines. A CoCo upgrade and jam session is in my future.
And the 3 didn't use the 6847, but a custom ASIC.
Fun stuff.
We were definitely into SEX in those days.
In the late 1970s I was working at Tymshare, and one of my tasks was maintaining the assembler and linker. (I think this was on the PDP-10 but it could have been another machine.)
We wanted a "weak external" feature, somewhat akin to a "weak reference" in modern languages: instead of failing to build if the external symbol was not defined in another object file, it would link OK but leave a null value that you would check at runtime.
The assembly directive for a regular external was EXTERN. I thought of calling the weak external WEXTERN but that looked silly. So I decided to call them Secondary Externals, with the directive being SEXTERN.
And as far as I know, no one complained!
https://www.atarimagazines.com/computeii/issue3/page52.php
John Draper (Cap'n Crunch) once creepily invited a friend of mine (who was a strapping young lad at the time) into the back of a van to "execute some 1802 instructions".
We used to drive around in his VW microbus finding interesting payphones. Then when he was learning to program, I visited him once in a while at his place in Berkeley to help him with his code.
My motivation was that he usually had some decent weed. Then one time he asked if I wanted to "work out". That lasted about two minutes until I found out what he really meant.
Many years later, I ran into John at the Homebrew Reunion. He didn't recognize me at first, so I reintroduced myself and mentioned how we used to hang out and write code.
His eyes lit up and he asked, "did we work out?"
Luckily, someone has already scanned that article. In fact, it looks like they recreated the article:
https://cdn.hackaday.io/files/460001968064000/byte_6809_arti...
Sure do miss BYTE. Would be excellent to have a similar publication today. The scope is larger, perhaps too large, but maybe not. One got such great perspective from the pages of BYTE.
The author's simulator runs fine on a 32-bit Windows machine. I would expect it to run under DOSBox just fine.
The simulator's text user interface is also superb. Getting the machine running with the full OS was very straightforward (run "D6809.COM W=CUBIX.DDI" to start with the OS disk mounted read/write).
Direct link to the archive: http://www.certsoft.com/PXK9_OS9_Source.zip
This seems to have been written in Pascal (Modula?).
I never really wrote any ASM for it though, but it inspired me to write a p-code based runtime that had 16 bit registers for the 6502.
The 96KB were done in a rather weird way, because there were really only 32KB of contiguous address space available once you accounted for ROM, and both the 6502 and 6809 had a 64KB address space anyway. So the SuperPET had 32KB contiguous RAM in the lower half of the address space, and 64KB of paged RAM occupying a 4KB address range somewhere in the upper half of the address space. The code for the Waterloo languages typically ran in paged RAM, split into 4KB segment, and when it needed to jump from one page to another, it used some trampoline routine to switch the page and jump back.
For FORTH, I used a simpler scheme: I ran in contiguous RAM and used the paged RAM for the FORTH explicit virtual memory system, because there you only needed to guarantee access to one page at a time so it mapped onto the hardware without much sweat.
Someone should do a Ben Eater style kit. I am very tempted!
ARM64 and RISC-V I would agree are very different beasts. One of the key differences I feel, is that caching and pipelining become much more important on these systems. Most (not all) ARM32 systems have very simple and short pipelines, and no cache. E.g. Cortex-M3 and -M4.
The historical reason for this is that ARM32 was directly modeled after the 6502, which in turn was based on the 6800, as was the 6809.
The conditional branch instructions (and set of flags) for all of these are from the PDP-11.
The instruction set and overall CPU complexity, and the hardware it's running on.
In my view, playing with assembly is best done while also either playing with hardware, or really understanding and having access to said hardware at the "raw metal" level. The distinction being computation, and that's not too much different of an experience, and making things actually happen, which can be a widely different experience!
The simplicity, again in my view, of 8 bit type hardware is very helpful. It's not so large and or complex. People can understand it reasonably well, and with some degree of effort, make things happen.
Back when I was learning assembly language, it was on these kinds of systems. Sometimes the hardware played a lesser role, say a machine that has serial i/o for use with a terminal. Other times, the hardware was far more prominent, like with home computers of the time.
With the terminal, one would typically setup the hardware for serial comms, and once that was all done, basically stuff values, from a buffer, into the designated address or capture them, into a buffer, as they arrived.
On a machine with built in display, the display was typically memory mapped in some fashion. Writing to a specific address in RAM would cause a character to appear on the display screen.
It was common to have a memory map of the computer handy when writing assembly language programs. Put a number here, or set a bit there, and things would happen, like maybe click a speaker, or change the color of the screen, turn a motor on, or make a sound.
Have you looked at the 6502 hardware tutorial kits Ben Eater is doing?
(I mentioned up thread the idea of doing these with the 6809, which is tempting me badly right now...)
They are fantastic! Assembly language + hardware functionality = your program.
And this is the embedded view on things too. Having everything simple and small generally means being able to make good progress and learn a lot without it being too heavy of a lift. And depending on what your interests are, frankly you might be able to do more than you would expect.
Should your interests lie in this direction, a 6809 is an awful lot of fun to program. It's one of the best 8 bit experiences, IMHO. Be warned though! It can be an addiction, and once it starts... you may find yourself with a scope, spiffy new tools, and the need for some space to work, and, and, and! Mine has been life long, first triggered by writing a line of BASIC, pressing carriage return (enter key these days), and seeing a light bulb turn on. :D Soon after that, it was a speaker click, then a loop to make sounds, then one with parameters to make different sounds, and, and, and... There you go.
But, it's not necessary to fixate on this chip either. It's a beautiful CPU, no doubt. But others are also fun, and they have their advantages and there is a wide variety of hardware out there to program in and with.
If this kind of thing does not appeal in some way, then yes! By all means explore assembly language on something newer, bigger and faster.
Or, maybe it is, and or you don't know.
I would suggest emulation. We've got pretty great emulation for all the old machines.
Many of us, who enjoy these older CPUs, work with emulators, because we've got access to modern tools and such that make life a whole lot easier.
While there is something to be said for an authentic experience, to be frank? It's a lot of work, and kind of painful most of the time.
A good emulation smooths away a lot of pain points and "nicer" is a lot less important. Use an older CPU, newer one, freely. And you can save states and all the other good stuff that makes learning less painful and more fun and fruitful.
Right now I've got a little 6502 project in progress for an Apple //e type computer. It's being done in an emulator, and from time to time I move it all onto the real computer just to see it all go and interact with it for real, and or check it out at different clock speeds, or just show off.
But the majority of the time developing is on emulation. I can fire it up, make a little progress, or explore an idea, and then save everything for the next step later. In this way, it's easy to jump in for an hour, have some fun, and get back out again when that hour isn't costly in some way.
Probably more here than you wanted. Hope it helps.
I haven't ever really tried to dig into a lot of details on assembly with the contemporary processors though. I know there are quite a lot of extra capabilities, for example various things for efficient vector math and virtualization, but don't know a lot of details. So I was just wondering what people thought about doing assembly on the latest CPUs compared to the old ones. But I think as you point out, a lot of that depends on what hardware you are interfacing with and how and more generally the application.
I think you are right to point out that the details and capabilities of the hardware interfaces are going to make a huge difference. That is something that is attractive to me about assembly programming, especially olders systems that are designed to be interfaced with assembly, is that hardware capabilities are directly accessible and you can achieve interesting things straight away just by putting some numbers into memory.
So a few years ago I built this thing called Vintage Simulator https://vintagesimulator.com/ and one of the ideas I had was about directly accessing interesting hardware capabilities. For example, the system provides Lua scripting, and I created a way to interface with the RAM on the emulated systems. So I started working on the idea of a virtual 3d spaceship controlled by an onboard C64. I was making it so that I would put things like the elevation of the ship into memory with Lua, and then with C64 assembly I made a read out on the screen. I was planning on making so the assembly program could control the ship, with the Lua program monitoring special memory locations.
Also along those lines, I was dreaming about making a virtual 3d holographic vector display. So it could maybe monitor certain memory locations or something and then to display into the 3d environment from the emulated 8 bit computer, just write to memory. Or maybe write to some kind of output system if that made more sense.
Fun to think about.
Given this context, I have a few thoughts:
Contemporary processors may be interesting when simplified some. Your projects make me think about the Zachtronics games.
http://www.zachtronics.com/tis-100/
That is an assembly language game with surprising depth. People, who play it seriously will learn quite a lot.
Using older hardware in tandem with current is a lot of fun. The terminal, for example, still does exactly what it was designed to do and is still useful today. A C64 has a user port for this kind of thing. Apple 2 computers saw all manner of expansion cards capable of data capture, control, computation... making ones own card with a PIA was a standard type project, just as connecting a circuit to the user port was. BASIC was often enough for many basic controls, say regulating temperature, or turning things off and on based on time, or other data states, assembly language brought more of the speed possible, and with more speed, we get more posibilities.
Take one bit wired to a speaker. That is what the Apple and IBM PC shipped with to make sound. The PC had a spiffy timer to bang out notes, and the Apple had nothing but a toggle. Speaker on, or off.
Here is where the fun part was back in the day:
At first, it seems useless. Access an address and the speaker pops out. Do it again, and the speaker pops in. One can type this right into the computer with a BASIC POKE statement, or the monitor by address and watch the speaker change states.
A loop gets one some clicks rapidly, or maybe a buzz, depending. But in assembly language a lot more is on the table! Suddenly one realizes it is possible to turn the speaker on or off long before it has reached the other state. There are lots of other realizations, such as what a read modify, write instruction does compared to one that does a single read or write.
There are any number of simple, seemingly shallow examples out there, racing the beam, making sounds, cramming more onto a floppy, and so on.
But what happens when the hardware is simple, driven by software gets right at the heart of assembly language, in my view. Hardware may be designed to do something, and if designed reasonably, will do that thing.
But, where it may be simple, or over engineered, has bugs, whatever, all suggest more, and as time passed we saw people get far more out of a lot of hardware than intended. Demoscene comes to mind here.
Maybe four thoughts! You should definitely take a look at this guy:
https://m.youtube.com/watch?v=jmTwlEh8L7g
Here is the assembly programmer mindset modeled well. People generally approach it wanting to get more out of their hardware, or understand what is really happening better, or to help them with subtle program errors.
Some do it for fun too.
This work suggests the ideas evolved during early computing, hacking on hardware, exploiting bugs, design choices, and more continue to play out on modern processors and systems just fine.
Keys to the kingdom for those willing to play.
The serial ports on the back were attached to 6551 UARTs. The keyboard is parallel.