BBC BASIC on the AgonLight2 - Modern Z80 single-board computer

I take a closer look at the AgonLight2, running the standard image with MOS operating system and BBC BASIC.
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[@slithymatt]

As I predicted, there are cases you can now 3D print yourself: www.printables.com/model/422272-agon-light2-cases Also, Olimex now sells a nice metal case, which I have coming. If you live outside the EU, shipping is very pricey, so you may want to try just have someone local print one for you, if you don't have your own printer.

[@tomwilson2112]

Just FYI, that case doesn't quite fit together properly; it rubs the Reset button, and it doesn't quite lock together on the front. It works, but I'm a little disappointed with the fitting on this one.

[@RichardHallas]

Note that Agon MOS has some similarities with Acorn’s MOS. As such, (a) *-commands can be typed in lower case (it’s only BASIC commands that must be in all caps), and (b) cataloguing a directory can helpfully be abbreviated to *. (full stop/period character).

[@dannixon247]

Very excited to see content that is covering this exciting new Dev platform... Thx

[@Zeem4]

A few years ago I wrote a PDP-8 emulator in BBC BASIC, using both RISC OS on a Raspberry Pi and Richard Russell's BBC BASIC SDL. I wonder how fast it would run on this hardware.

[@slithymatt]

That would be pretty neat! Is your code on GitHub or something?

[@RichardHallas]

That'd be a great thing to port! (Maybe after the next system software update, since there are some useful changes coming soon.) In the meantime, is your RISC OS version available to download?

[@Zeem4]

@@RichardHallas See my other comment - it's on GitHub but I can't remember if it's in Russell's SDL format or RISC OS format.

[@RichardHallas]

@@Zeem4 Found it. As I rather expected(!), it's in SDL format - which is a pity, as (as a RISC OS user myself) I'd be more interested in the RISC OS version…

[@Zeem4]

@@RichardHallas I must have a computer round here somewhere with BBC BASIC SDL on it (plus Matrix Brandy probably), if I remember I'll export it as plain text. Several times I switched between the two as I was playing about with it. The current version might need some alteration as I think I ended up with an interval timer handling the keyboard which isn't available on RISC OS BASIC, but the original code might still be in there but commented out.

[@thebyteattic]

Great video again! The eZ80 does have a 24-bit address bus, but it is still an 8-bit CPU, even in its extended mode. What determines whether a processor is 8-, 16-, 24-, 32-bit and so on, is the width of the data bus and, therefore, of the data memory. All 8-bit processors of old also had 16-bit address buses, so this is entirely normal. In Agon light, both the data bus and data memory are always 8-bit wide, in both compatibility and extended mode, so Agon is unreservedly a true 8-bit machine. The Quark BASIC interpreter already uses extended 24-bit instructions for extra performance, even though it is a fully 8-bit implementation of BASIC. Agon light also has multiple screen modes. The highest resolution is 640x480, with up to 64 simultaneous colors.

[@brucemcfarling4674]

The 8088 was not considered an 8bit processor, even though it had an 8bit data bus. It would simplify things if there really were these hard and fast definitions for all worlds, but in real world language, lots of words are used in different ways by different people. For some people, the 24bit registers, operations and ALU mean the eZ80 is like the 8088, a processor with an external data bus smaller than its internal bus.

[@zxspectrum16KB]

How many colour palette?

[@ChipGuy]

I like that the board is reasonably priced, but what I miss is that the upper address lines and the programmable chip select lines are not used and not available on a real expansion connector. I would have likes that board to have a high density expansion connector on the bottom to I could use it as a main board for a backplane of some sort.

[@thebyteattic]

This is a fair point. We do provide two dozen GPIOs that people can use to connect to all kinds of cards, sensors, actuators, etc. A full bus expansion connector would have made the system more expensive, as it requires tristate buffers, loads the buses (thereby requiring more careful layout and perhaps impedance control during PCB manufacturing), etc. So for #AgonLight we decided to go without it, even though the original prototype did have it. Remember that Agon runs at almost 20MHz; this isn't an 8MHz system.

[@talideon]

There's a jumper on the board that will cause the audio to go through the buzzer. It's BUZ_EN1. The audio jack is mainly there for if you want to be able to record the audio, and the sound you get through the buzzer is the same one-bit audio. I'm guessing the jumper was a simpler solution than sensing the impedance on the audio jack for output sensing.

[@thebyteattic]

If you insert an audio jack, the buzzer will be disabled, regardless of the jumper. The jumper is there just in case someone dislikes the sound of the buzzer, and wants to disable it even when no speakers are plugged in. And it serves the extra purpose of providing an easily-accessible header for those who want to wire the audio signal to an amplifier (several people did it, while constructing their own custom cases).

[@talideon]

@@thebyteattic Ah, cool! Thanks for the clarification.

[@michaelcloutier2225]

The Two headed addapters you are talking about have a USB HOST CHIP in them that actively bridges the PS2 Devices as HID USB devices. What you are looking for is a simple passthrough cable that came with Devices that had PS/2 / USB factuality chips as the Amazon KB has. Any KB with a PS/2 connector will work on that port with one of those passthrough cables. I have several of them.

[@richy69ify]

This is a bargain. Cheaper than modern little tune-ups for old 8-bit machines.

[@nicholsliwilson]

The trick with the feet on Olimex boards is to use needle-nosed pliers to pull the nub through the mounting holes, @The Retro Desk

[@slithymatt]

I will probably use one to get them out! I have a case shipping to me right now from Olimex.

[@nicholsliwilson]

@@slithymatt honestly never tried getting them out before. 😄

[@spinnetti]

Impressive little machine!

[@talideon]

The extra mystery port is for the rare occasions when the eZ80's firmware needs to be updated. I don't think it's strictly needed after the boards are manufactured.

[@avalonbits]

Yup. There is an utility to flash the firmware from the SD card so that port is really only needed when flashing it for the first time.

[@thebyteattic]

The ZDI port is only required for sellers, who need to program the Agon firmware for the very first time.

[@johnwilliams7999]

would love to see some more videos on this system! Purely for selfish reasons...i just bought one but have no idea on how to use it lol

[@slithymatt]

Got one coming very soon!

[@TechCowboy]

This is more like what I expected of the original X16 to be.

[@slithymatt]

The Gen3 version will be more like this, but entirely implemented on a single FPGA, or possibly an ASIC

[@brucemcfarling4674]

Entirely or mostly? An FPGA with enough internal RAM for the LowRAM, HighRAM, VeraRAM and to hold the ROM code would be a bit pricey if it exists.

[@slithymatt]

@@brucemcfarling4674 I meant the logic entirely implemented on FPGA or ASIC. Of course it makes more sense to have memory as separate off-the-shelf packages.

[@brucemcfarling4674]

@@slithymatt Yes, hence the 2chip vs 3chip vs 4chip issues ... two FPGAs of the type Vera was designed for, one holding Vera and the other holding everything else. That lets HighRAM be a single 512KB SRAM because the onboard 1Mbit can host LowRAM. Then a 512KB FlashROM makes a 4chip design.

[@RoboticParanoia]

I have a proprietary access control device powered by a Z80 equipped with a 2 lines LCD, alphanumeric keyboard, barcode reader, fingerprint reader and Ethernet. I wonder if I can repurpose it.

[@slithymatt]

Probably! Does it have a reprogrammable ROM on it?

[@GarryGri]

Is the Basic completely BBC compatible, specifically does it have mode 7 (Teletext) text/graphics supported? Also does the BBC Basic still allow Machine Code to be run from within it?

[@slithymatt]

Both good questions, but I haven't looked into it that far. I would imagine you could jump into a machine code program at a given address, but I haven't seen an example of that yet.

[@silasdenny3267]

This computer is interesting,. My family's first computer ran CP/M, and my hobby is working with single board computers. I would like to what it takes to get CP/M running on this.

[@slithymatt]

That will be coming soon!

[@michaelcloutier2225]

The reason that KB/Mouse adapter did not work was that it has a host USB chip in it to convert both interphases to USB. You need just a passthrough passive adapter that often came with duel PS2/USB devices.

[@slithymatt]

Yep, that's what I did and it works fine now.

[@tonedef71]

I am not aware of any case, box, or enclosure available for the AgonLight2 at this time from Olimex or elsewhere.

[@slithymatt]

Yes, I should have clarified that the case designs are for the original AgonLight, and would need to be modified for the AgonLight2. Since it's all open source, that will exist very soon, hopefully.

[@slithymatt]

AgonLight2 cases are now available at Olimex (for 10 Euro), and soon from The Pi Hut for distribution in the UK.

[@mybricology7388]

Hello, at 1:52 you say that the Z80 ALU was only 4 bits. This is wrong it was 8 bits. I will really appreciate to know your source of information about the fact you're saying that. greetings

[@slithymatt]

web.archive.org/web/20130909224112/www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-how-it.html

[@mybricology7388]

@@slithymatt yet I saw the link insinde a comment of a Z80 Spectrum ASM course. Thanks

[@alexany4619]

Why are the graphic commands not implemented in Basic, instead you have to use these cryptic VDU-commands?

[@slithymatt]

Mainly, it makes the BASIC interpreter itself simpler and offloads all of the graphics stuff to VDP. It's how the original BBC Micro worked, back when ROM space was at a premium.

[@alexany4619]

@@slithymatt Doesn't has BBC-Basic e.g. the commands Draw, Move and Plot regularly?

[@slithymatt]

@@alexany4619 yes, and the Agon has all of those. Just like with the BBC, those are convenience functions for certain VDU commands

[@jimtekkit]

I thought this would just be another forgettable linux SBC running emulators or something, but my ears pricked when you mentioned the eZ80. I've been thinking about building a Z80 (or eZ80) computer where all the I/O is handled by an external microcontroller and so this is overall very similar to what I want. Might pick one up to experiment with!

[@RichardHallas]

It's a great system with real potential. It deserves to have people developing things for it.

[@SpeccyMan]

The Z80 version has already been done. See Z80-MBC2.

[@vaelenorg]

Nice! Good work as always. :)

[@revietech5052]

I have that exact same ps2 perixx keyboard and seems odd that it wont work with the al2. It suggests something wrong with the al2 itself.

[@slithymatt]

It does work, just not with my two-headed PS/2-USB adapter. It works fine with my simple passive adapter

[@revietech5052]

That's good to know

[@zxspectrum16KB]

How many colour palette?

[@revietech5052]

Can you play bbc games on this from websites like stairwaytohell?

[@slithymatt]

If it is written in BASIC using strictly console and drawing commands, then maybe. If it's poking memory at all or depending on anything specific to the hardware, no.

[@MrWaalkman]

Using a PS/2 connector would have been a better choice. And my boards cost 121.15 euros for two of them with shipping. Which works out to $130 for two, $77 for one.

[@slithymatt]

The original Agon and AgonLight used PS/2 ports, but those were limited runs. I'm not sure why Olimex went with the USB-A, but you can still use a PS/2 keyboard with a passive adapter

[@richy69ify]

@@slithymatt Olimex sell a PS2 (with USB connector) keyboard for 12 euros

[@frankowalker4662]

Is it possible to write your own BASIC ROM for this and ditch the BBC version ?

[@slithymatt]

Sure. It's not on ROM, though, it loads from the Micro SD, so you could compile your own eZ80 binary and boot to that.

[@thebyteattic]

Yes, you can reprogram the firmware of both the CPU (running BASIC) and the video co-processor (running all the graphics and sound routines) entirely. You can code the firmware in ANSI C using the free ZDS-II IDE (for the CPU) and the Arduino IDE (for the video co-processor). In other words, you can make Agon entirely your own, either starting from scratch or from the firmware provided. You need no licenses or permission. And you may commercialize it too.

[@frankowalker4662]

@@thebyteattic Brilliant. Thank you. :)

[@alastairhewitt9462]

It's not all "fixed logic'. The board has an ESP32 on it. I believe that is a Xtensa dual-core 32-bit LX6 microprocessor operating at 240 MHz. It clocks in around 600 MIPs vs. a typical 1980's Z80 that would be around 0.43 MIPs.

[@slithymatt]

A microcontroller is fixed logic. You can't change the transistors around! It's running software right alongside the eZ80.

[@zxspectrum16KB]

Can she handle full screen animation? 1.2mb a second no?

[@slithymatt]

Good question! I don't know if anyone has tried

[@djcsdy2]

There's something unsettling about seeing MOS and BBC Basic running on a Z80.

[@SpeccyMan]

So the Cambridge Z88 never entered your radar?

[@djcsdy2]

@@SpeccyMan huh! No it did not! I'm not sure why. Thanks for sharing!

[@AlexanderWeurding]

IPX?

[@zxspectrum16KB]

Why isn't it clokked at 50mhz? Why isn't there 16mb of fast dualported video ram as well as 16mb of ram?

[@earthsteward70]

Its gonna be crazy to see what people can do once assemblers are written for this thing.

[@slithymatt]

The hope is that original CP/M assemblers will run on it once the OS port is done.

[@SpeccyMan]

BBC BASIC has an assembler built in.

[@michaelkaercher]

I was thinking about buying a old platform or the commander x16 or this one. But I cannot really find any reason to do so. The miserable screen resolution, the slow operation, the lack of network, there is nothing attracting me. The 8-bit guy did say that it is about understnding the thing end to end. OK. Just buy a microcontroller for 3 Euro. You can understand that end to end. There is just no case.

[@zxspectrum16KB]

16mb of video ram?