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Agon 8-bit development progress


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Whilst waiting for the X16, I thought some of you might be interested in checking out the progress on the Agon Z80 based 8-bit computer, developed by Bernardo Kastrup. This computer will be released fully open-source and will feature a eZ80F92 CPU+Flash running at 18Mhz, 512KB of onboard SRAM, 128KB flash, with onboard SD card, PS/2 and expansion port with SPI, I2C, 20 GPIOs.

It will have a separate A/V subsystem based on the ESP32-PICO-D4 chip, capable of running FabGL libraries and more, output over VGA and will boot-up immediately into BBC Basic. Both CPU and AV subsystem can be fully programmed by the user, so the entire system can be hacked.

All components are currently available, with projected costs for the BoM around 50 euro. The non-profit Dutch HomeComputerMuseum will sell it in a fully-populated, ready-to-use format, +/- summer timeframe.spacer.png

 

Latest progress:

 

 

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Well, that's pretty much what I would consider a perfect modern 8 bit computer. Probably cost 100 EUR fully assembled and shipped, which is about 138 CAD. I guess that's fine. However...

Is there something that this version of BBC BASIC can do that the version included with RISC OS for the $7 Raspberry Pi Zero cannot? If not, then a person who is only going to use BASIC does not need this product, because the Pi0 can boot to BASIC almost instantly while also being compatible with USB keyboards and HDMI monitors, which I imagine would be more convenient than PS/2 and SVGA. This is not a complaint, but a legitimate question, does the Agon have hardware capabilities exposed to BASIC that make it better than running BBC BASIC on something else? I Googled, but did not find an answer.

It will be interesting to see what assembly programmers can do with the machine.

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On 4/5/2022 at 4:41 PM, Tatwi said:

Well, that's pretty much what I would consider a perfect modern 8 bit computer. Probably cost 100 EUR fully assembled and shipped, which is about 138 CAD. I guess that's fine. However...

Is there something that this version of BBC BASIC can do that the version included with RISC OS for the $7 Raspberry Pi Zero cannot? If not, then a person who is only going to use BASIC does not need this product, because the Pi0 can boot to BASIC almost instantly while also being compatible with USB keyboards and HDMI monitors, which I imagine would be more convenient than PS/2 and SVGA. This is not a complaint, but a legitimate question, does the Agon have hardware capabilities exposed to BASIC that make it better than running BBC BASIC on something else? I Googled, but did not find an answer.

It will be interesting to see what assembly programmers can do with the machine.

Yeah, it's a very interesting new platform to discover Z80 assembly. It's not meant as a pure Basic platform, but the small group currently developing it, has selected BBC Basic v4 as a jumpstart for future users to explore it further.

Nothing would prohibit me from developing an entire different firmware/OS for it. I imagine this will easily create an opportunity for others to create interesting stuff. 

And if all one would want to do is flash a flew leds from basic, even create some vga graphics, I agree it is hard to beat the pricepoint of a Pi Zero or even pico, great platforms on their own (I own both), but these are not a true 8-bit platform that some of us love to explore and tinker with.

Edited by Jeroen
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It’s a client server model. Effectively a 30Mhzish z80 equivalent (its pipelined) but extended, flat 24 bit address space. 512M of RAM. I/O done by an Esp32 via a serial port, so it isn’t going to be a direct bitmap access, likely to operate at next level up. Serial PSRAM for graphics storage. Likely cost sub $100

The ez80 is a z80 with 24 bit address pairs. Takes a little getting used to, because you can forget this ! It can do a compatible z80, bit like the 65816.

Edited by paulscottrobson
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On 4/5/2022 at 3:41 PM, Tatwi said:

Well, that's pretty much what I would consider a perfect modern 8 bit computer. Probably cost 100 EUR fully assembled and shipped, which is about 138 CAD. I guess that's fine. However...

Is there something that this version of BBC BASIC can do that the version included with RISC OS for the $7 Raspberry Pi Zero cannot? If not, then a person who is only going to use BASIC does not need this product, because the Pi0 can boot to BASIC almost instantly while also being compatible with USB keyboards and HDMI monitors, which I imagine would be more convenient than PS/2 and SVGA. This is not a complaint, but a legitimate question, does the Agon have hardware capabilities exposed to BASIC that make it better than running BBC BASIC on something else? I Googled, but did not find an answer.

It will be interesting to see what assembly programmers can do with the machine.

Probably less than that, though shipping to Canada you never know.

The answer to your question is "it isn't done yet", but likely not, significantly, more complex than Basic V. The problem is it's essentially the same product as the X16

  • Modern version of classic CPU (though the eZ80 is significantly faster and has a 24 bit address space, the instruction set is an expanded Z80 (e.g. you can do things like LD DE,(HL) ))
  • RAM about the same 512M on the basic model.
  • Graphics and Audio handled by a seperate modern part via a fast serial link. The design of the link is more client/server I think than "Poking bitmaps" (though you probably will be able to poke bitmaps), so probably commands to draw lines/polygons etc. rather than bit tweaking. I think the graphics is based on FabGL though is likely to be extended.
  • VGA/PS2/SDCard connector.

Differences:

  • There's no ROM other than that on the eZ80 and initially it will be an X8 design viz. boot off the SDRAM card
  • The "VERA" equivalent is an ESP32 not an FPGA.
  • It is less practical to build as its entirely SMT though it is open source (I think)
  • Uses a cheap PSRAM chip to provide storage for graphics/audio stuff (8Mb I think)
  • The eZ80 has a 24 bit address space - HL DE etc. register pairs are now 24 bits wide (it can be put into Z80 compatibiilty mode)
  • It's only 6 bit colour.
  • No "real" audio chip.
  • Direct code load port.
  • USB port. Don't know flexible it is, e.g. could you plug a mouse or gamepad in ?

There's a reasonable question of "why not use a Raspberry PI" or similar, which is perfectly valid. The same criticism could be made of the Commander X16, and pretty much all the other retrocomputer projects and was made repeatedly at the start of the X16 project.

Does it give you something better ? Not really, but none of them do, save for programming on a modern version of an 8 bit CPU.

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It is probably best suited for assembly programming, like the rest of the 8 bit systems, and that's totally fine. Being entirely open, it is possible that folks could write a BASIC compiler which translates custom BASIC commands into efficient machine language routines, so one could write all of an advanced program in BASIC. So that's interesting. 

It should be noted that this project is headed by that dude who had some pretty crap criticism of this community. Nice product, excellent follow through, but I'm not real keen on where it's coming from.

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On 4/11/2022 at 7:01 AM, Tatwi said:

... It should be noted that this project is headed by that dude who had some pretty crap criticism of this community ...

Yeah, that post didn't make a lot of sense and followed the typical "If I didn't invent it, it's garbage" mentality. Either way, I wouldn't enrich him by one penny after reading that post. 

 

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"The purpose of engineering" is, apparently, to drain the joy out of hobbyist activities by imposing arbitrary rules on projects in order to rule out what one is not interested in and rule in what one is interested in.

It seems like he posted that on his blog because when he posted his arguments on the Facebook group, people on did not jump up and down and shout about how brilliant he was and how wrong they were to be interested in the CX16.

Edited by BruceMcF
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On 4/11/2022 at 4:04 PM, SlithyMatt said:

Bust rest assured, this system is "correctly designed" according to the guy who designed it.

It's very similar to the CX16 design. (with a few advantages ; it's faster, no paging and so on). It's just engineered in a coherent fashion. And it exists without burning 5 figures.

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Did he criticize the community?  Seemed like he was criticizing the product. Not defending him but I call it like I see it. And I can’t say he doesn’t have some good points. The X8 is looking better and better, I have to say.

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On 4/11/2022 at 6:50 PM, paulscottrobson said:

It's very similar to the CX16 design. (with a few advantages ; it's faster, no paging and so on). It's just engineered in a coherent fashion. And it exists without burning 5 figures.

It probably didn't include a preorder for scads of keyboards, either. Just because someone has burned five figures on a project doesn't mean that all that money was spent on prototypes.

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On 4/12/2022 at 2:53 PM, x16tial said:

Did he criticize the community?  Seemed like he was criticizing the product. Not defending him but I call it like I see it. And I can’t say he doesn’t have some good points. The X8 is looking better and better, I have to say.

There is a difference between making some good points and making a solid argument. He says "Engineering projects start with a clearly defined purpose and a set of constraints. Engineers then do the best they can, with the resources available within those constraints, to achieve the stated goal." and then proceeds to completely ignore the stated goal that David did not feel that he could recommend an original 8bit home computer to people new to 8bit computing who write and ask for a recommended starter system.

The argument has the common tell-tale of relying on a rhetorical question that he answers himself to quickly rush past one of the weak links in the argument: "If the offending element that breaks the purpose-centeredness of the machine is the FPGA board, why did they choose to use it? Because they wanted the video performance it brings with it. So performance was their goal, right?"

First, you have to accept that to serve any educational purpose, it is necessary to understand the system down to the gate level. This is a false dichotomy fallacy, where any education value in understanding a system down to the chip level is simply treated as beyond the scope of possibilities.

Then you have the core gap ... he offers an unnecessarily vague answer to his rhetorical question, when the more precise answer is "for performance as a hardware sprite / tile display chip" ... which would render his follow-up rhetorical question, "If you want performance, you go for a beefier, modern 8-bit MCU and faster, cheaper SDRAM" a non-sequitur.

However, to my mind, any criticism of the community is, however, only oblique, in the sense of implying that some elements of the community want some things that he implies it is irrational to want. For example, his argument seems to imply that it's not rational to want to build the X16 if you don't want to also dive deep into the FPGA programming & underlying hardware functioning of the FPGA fill-in for the missing VGA compatible hardware character / sprite graphic chip. From his argument, it would appear to be irrational to be willing to view Vera as a black box to be understood at the same level we understand the ASIC chips in the system.

Whether the eZ80 is an 8bit processor or not is open to debate ... unlike the 65816, as another example of an 8bit CPU expanded to support a 24bit address space, it has a 24bit ALU, Some would argue that it's a 24bit processor with a compatibility layer to run code written for its 8bit predecessor. It's not the kind of debate I would pursue, but after seeing debates over whether the 65816 is a "true" 8bit CPU, it's clearly the kind of debate that some people would pursue.

The quite reasonable observation that the CX16 system does not have a laser focus on implementing one specific design goal, but rather has a bit of a mish-mash of features has the flip side that many of those features might bring joy to some element of the 8bit Guy's audiences (plural, since he is, after also, "the 8bit Keys guy").

 

Edited by BruceMcF
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Besides... watching David's channel, it is clear that he has a special love for the VIC-20;  so it's completely understandable why he uses it as a foundation.  

Yeah 8BG needs no defending, but I grok it.  If I were an engineer* I might've started with the PET, for the same gut-reason that that's the first computer I learned on (although it does actually look like the VIC is a better starting place).

 

* I'm comp. sci.  It may be in the engineering college, but...

Edited by rje
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Guys, I didn't like what I read in Kastrup's post, either, but he has a right to an opinion. Regardless of how Mr. Kastrup has presented himself, we have a responsibility here to keep it classy and not resort to ad-hominem attacks on anyone - even if we dislike what they have to say. And this board is not a place for profanity. In case it needs to be spelled out, discussion here should always be appropriate for all ages.

Thanks

 

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On 4/13/2022 at 7:11 AM, rje said:

I might've started with the PET, for the same gut-reason that that's the first computer I learned on (although it does actually look like the VIC is a better starting place).

I agree. In fact, the current design is more like the Mini PET than it is the VIC-20. The Mini PET has a dual-port memory chip, which isolates the CPU and the CRT controller. I won't get into the details of how the CRT controller works, but the short version is that the PET does not use the same CPU/GPU interleaving that the VIC series does. That's where the similarity ends, though - the PET uses several counters and a bit shifter to generate the pixel matrix, along with some logic gates to sum them to a composite signal. (I'm not actually sure if the original PET used dual port RAM, or if it simply ran the video cycle during Phi 2... that's worth some research.)

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On 4/13/2022 at 12:35 PM, TomXP411 said:

Guys, I didn't like what I read in Kastrup's post, either, but he has a right to an opinion. ...

Indeed, much of the weakness of his argument seems to involve an effort to "objectively prove" what is in part a matter of opinion and preference, and that is not effectively answered if we lapse into the same approach.

A benefit of attempting to make a hardware project for a cluster of related communities of interest is that if, in the end, it turns out to satisfy enough people in those communities of interest, the number of people who are NOT satisfied with it or interested in it is beside the point. In a project where "thousands" would be a runaway success rather than an abject failure (imagine if the C64 had "sold thousands"!), on a world of 7.9billion, it very much does NOT have to make EVERYONE happy to succeed and thrive.

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^ As we say in the software world, "code wins arguments".  We can spend days arguing over algorithms, but there's no disputing a working solution.

 

 

Edited by rje
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On 4/13/2022 at 7:57 PM, BruceMcF said:

Indeed, much of the weakness of his argument seems to involve an effort to "objectively prove" what is in part a matter of opinion and preference, and that is not effectively answered if we lapse into the same approach.

A benefit of attempting to make a hardware project for a cluster of related communities of interest is that if, in the end, it turns out to satisfy enough people in those communities of interest, the number of people who are NOT satisfied with it or interested in it is beside the point. In a project where "thousands" would be a runaway success rather than an abject failure (imagine if the C64 had "sold thousands"!), on a world of 7.9billion, it very much does NOT have to make EVERYONE happy to succeed and thrive.

I like your hat. I wear a straw hat of a similar style around the yard, but it's not something I really would have thought I would wear. My dad wore one like it when he was gardening, so I picked it up for giggles when we were in Cuba a few years ago. But ya know, I quite like your hat, Bruce, and I wonder... would something similar suit my ugly mug? I do need a new hat before bald spot burning season begins...

Edited by Tatwi
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On 4/13/2022 at 3:11 PM, rje said:

Besides... watching David's channel, it is clear that he has a special love for the VIC-20;  so it's completely understandable why he uses it as a foundation. 

I'm a big fan of the SC/MP but I wouldn't use it as the basis for anything designed to be used now.

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