"Strawberry" Homebrew Computer System

[Astal4]

Hello! I'm.. Announcing? I guess... A computer system I'm working on!

 

I was personally very disappointed in the Commander X16 (Commodore derivative), MEGA 65 (Recreation at a high price), and am not too interested in the ZX Spectrum Next (Enhanced clone) or any of the other systems that are either clones or derivative of older ones. So I'm creating my own.

 

It's currently just the codename "Strawberry" as in Strawberry Fields Forever.

 

The tentative speclist is...

 

Z80 @ 8.39MHz

A floating point coprocessor (either an AM9511A-4 or something custom built by me)

A "Programmable Block Transfer Unit" (Basically a blitter but I want to be fancy), aiming for 16.78MHz

128KB system RAM

19,200 byte framebuffer for 3 video modes (160x120x8, 320x120x4, 640x240x1)

8 oscillator 8 bit wavetable sound

4 system timers

DMA enabled system

Cartridge port, expansion port, and RGB video, along with an internal speaker and a 3.5mm output

VGA video output

PS/2 keyboard input

2 joystick ports (fully digital ports)

 

This is my major long term project, and I will be updating as I continue. I will be working on this over the course of likely at least a year. I would also like to be building a companion expansion cage for it, and a custom operating system. My goal is to be able to offer the system in a kit form for $99, but I can't promise anything with it being so early in development. I'd love to get this to a prototype stage and see what some of the talented developers here could do.

 

Wondering thoughts. I know these systems never take off beyond maybe 2 or 3 people who think it's cool but eh, I'd love to get something into the community and have a machine that's straight up fun to play with, with all new parts, that's accessible to users interested in the modern retro scene or in the modern retro scene but don't want to make a huge investment into something like a C65 or any of the other far more expensive machines.

 

Thanks everyone and have a great day!

Edited January 15, 2023 by Astal4

[+5-11under]

First of all, best of luck on your project. Have fun.

 

Personally, I prefer the ColecoVision resolution 256*192, but the 160*120 matches the Intellivision, so you're still in good territory.

 

I like your I/O choices. Easy and inexpensive to connect. If you want people to purchase, that's a good approach. I'd work hard to keep the overall price down to a certain level.

 

I think the other thing you need, if you want to sell a decent amount, is a reason for people to purchase. Maybe something different compared to other systems/computers, maybe just some good games. I'd also suggest a good way to program it, if you want others to program some games or applications.

[Astal4]

Thanks. The reason I chose 160x120/320x160/640x240 is they all integer scale to 640x480 so a non multisync VGA monitor can be used. The expansion connector is a Euro-DIN 96, it's cheaper than a big S100 style connector, for people to purchase, I would love to get this into the hands of developers and get some games going for an official launch. I have rough sketches of the case design and I would love to injection mold them but cost, so I can't do everything. But I'm hoping this is a fun machine for people. 

[r_chase]

I guess my only question is that...will it be compatible with any other sort of 8-bit computer? I can see Atari 8-bit enthusiasists buying this too, but I'm guessing this is a completely new system or something, so maybe an emulator made with a free-and-open-source Strawberry-based IDE would work...for Atari 2600 at least.

Good luck on your project though. I'm honestly rooting for you. ❤️

[Astal4]

5 minutes ago, r_chase said:

I guess my only question is that...will it be compatible with any other sort of 8-bit computer? I can see Atari 8-bit enthusiasists buying this too, but I'm guessing this is a completely new system or something, so maybe an emulator made with a free-and-open-source Strawberry-based IDE would work...for Atari 2600 at least.

Good luck on your project though. I'm honestly rooting for you. ❤️

Thanks for the kind words. It will not be compatible with any other 8 bit, as it is a completely new system. An emulator would be possible. I HEAVILY recommend the programmers to use the programmable interval timers for timing rather than the CPU clock for reasons which I'll share in the near future.

[jltursan]

Great project!. IMHO I think that with no palette and a max of 8 colors (digital palette, I presume), the graphics are severely crippled. No mention to the max color resolution of 160x120. 

 

Maybe 19K for video are too little?; but I would go for something beefier like 160x120x8 palettized or 320x200x16 with no palette.

 

Anyway, go for it!

[Astal4]

4 hours ago, jltursan said:

Great project!. IMHO I think that with no palette and a max of 8 colors (digital palette, I presume), the graphics are severely crippled. No mention to the max color resolution of 160x120. 

 

Maybe 19K for video are too little?; but I would go for something beefier like 160x120x8 palettized or 320x200x16 with no palette.

 

Anyway, go for it!

Thanks!

 

So the palette is the full RGB555 spectrum to choose from, or 32,768 colors, the color modes are 8 bit, 4 bit, and 1 bit, so 160x120 has 256 colors, 320x120 has 16 colors, and 640x240 has 2 colors. There's a look up table in RAM for the colors, 512 bytes on top of the screen buffer, where you put the color values, any 256 RGB555 colors. I could increase the video RAM though, the specs are tentative so lots of fun to be had with features.

 

Thanks for the kind words.

[jltursan]

Cool!; so there's a palette mechanism 😀

 

Any plans to implement some kind of raster interrupts (hsync, I'm assuming that vsync has already been tied to one 😉)?. Using timers you can program some raster effects; but usually having real hsync interrupts make things easier.

And about your "blitter"....hardware sprites support?, logical operations between blocks transferred?

[+atari2600land]

I thought it was called Strawberry as an alternative to Apple.

So is this like an 8 bit console or something bigger?

[Astal4]

9 hours ago, jltursan said:

Cool!; so there's a palette mechanism 😀

 

Any plans to implement some kind of raster interrupts (hsync, I'm assuming that vsync has already been tied to one 😉)?. Using timers you can program some raster effects; but usually having real hsync interrupts make things easier.

And about your "blitter"....hardware sprites support?, logical operations between blocks transferred?

So the "blitter" will just be a block transfer, can be used for anything, no specific sprites, but can move things around memory quickly, I'll likely set it up to address and move pixels around. The hsync interrupts i could look at adding as well. The fun part of using an FPGA for logic is I can add all this in progressively.

 

4 hours ago, atari2600land said:

I thought it was called Strawberry as an alternative to Apple.

So is this like an 8 bit console or something bigger?

8 bit computer, although the base form could easily be used as a console since the keyboard will likely be PS/2 detachable. It's just strawberry because I'm a music nerd

 

I'll likely be calling the expansion cage Penny Lane.

[Forrest]

The Agon Light seems close to the specs of your proposed system. The Agon Light was released last year and the specs are:

An eZ80 running at 18.432 MHz, system memory (parallel SRAM, 512KB), a µSD-card slot and several general-purpose I/O lines. The 'terminal' or Audio/Video subsystem contains an ESP32-PICO-D4 system-on-a-chip running at 240 MHz, 8MB of memory (pSRAM) and ports for video (VGA), audio and keyboard (PS/2). Agon™ takes 5V input power either from its USB or GPIO port.

 

The developer's website is https://www.thebyteattic.com/p/agon.html

 

Olimex is taking pre-orders for an assembled version for 50 pounds at https://www.olimex.com/Products/Retro-Computers/AgonLight2/open-source-hardware

Edited January 22, 2023 by Forrest

[Astal4]

12 hours ago, Forrest said:

The Agon Light seems close to the specs of your proposed system. The Agon Light was released last year and the specs are:

An eZ80 running at 18.432 MHz, system memory (parallel SRAM, 512KB), a µSD-card slot and several general-purpose I/O lines. The 'terminal' or Audio/Video subsystem contains an ESP32-PICO-D4 system-on-a-chip running at 240 MHz, 8MB of memory (pSRAM) and ports for video (VGA), audio and keyboard (PS/2). Agon™ takes 5V input power either from its USB or GPIO port.

 

The developer's website is https://www.thebyteattic.com/p/agon.html

 

Olimex is taking pre-orders for an assembled version for 50 pounds at https://www.olimex.com/Products/Retro-Computers/AgonLight2/open-source-hardware

Interesting, however I'm going to be building a hardware video system rather than using an ESP32 or something, it's going to be more in the 80s style, but I might pick one of those up to play with. This project is somewhat on the back burner right now as I've fallen in love with the Apple Newton for some stupid reason.

[Astal4]

Project is dead, however! There is a "Saturn" computer project that I have developed to a CAD schematic so far within the past few days, I think I'll be spinning up some boards soon. Completely new, unrelated design, it uses a full Zilog chipset on the mainboard with all 74 series logic minus a MAX232 and the ROM, RAM is a daughterboard... More details coming soon if anyone's interested. 

[jltursan]

Sure, any info will be welcome!

 

What are the key differences between both projects?, what do you mean by "full Zilog chipset", CPU+CTC?

[Astal4]

On 3/13/2023 at 9:38 AM, jltursan said:

Sure, any info will be welcome!

 

What are the key differences between both projects?, what do you mean by "full Zilog chipset", CPU+CTC?

Full Zilog chipset being CPU (Z84C00) + PIO (Z84C020) + CTC (Z84C030) + SIO (Z84C040)

 

The details are still somewhat TBD, but here goes.

 

10MHz clock speed

Hot plug serial data cards as an analogue to floppy diskette

4 expansion slots

1 higher DMA priority video expansion slot

RAM slot with support for up to 512KB RAM, possibly will increase to 1MB or 2MB if I see it needed

CP/M Plus BIOS, will run CP/M 3 out of the box via the onboard RS232 port, or a custom TBD mouse driven OS, built for CP/M 3 platforms.

Built in keyboard controller (8 rows by 16 columns)

Built in "serial expansion" slot for things like MIDI, joystick breakouts, probably mice, and other serial devices, with baud rates from 31250 to up to 2M. TTL level

Built in RS232 serial port

Up to 10Mbit/s serial speed for serial data card, size will likely be 512KByte, aim to write a floppy diskette compatibility layer in BIOS for it.

[+5-11under]

What is the CTC? I can't find that part number Z84C030.

 

[Astal4]

11 hours ago, 5-11under said:

What is the CTC? I can't find that part number Z84C030.

 

I'm sorry, typed it late, Z84C00, Z84C20, Z84C30, and Z84C40

[+5-11under]

How will you do video?

[Astal4]

2 hours ago, 5-11under said:

How will you do video?

There's a couple ideas up in the air for video, the major two are a second Z80 with a firmware to do graphical tasks, or an FPGA core with an era appropriate sprite engine in it. Sound will also be on the same card, the same implementation as my 7800 wavetable sound chip that I am working on. 

[jltursan]

My vote goes to an FPGA core. Dual CPU systems (main+video) are hard to program: two separate RAM banks, tiny shared memory, semaphores...or maybe you've a cleaner approach?

 

I've always considered the V6z80P of Retroleum the perfect example of a superb FPGA video graphics card implementation. Paired with a real Z80 is a really nice machine.

 

[Astal4]

8 hours ago, jltursan said:

My vote goes to an FPGA core. Dual CPU systems (main+video) are hard to program: two separate RAM banks, tiny shared memory, semaphores...or maybe you've a cleaner approach?

 

I've always considered the V6z80P of Retroleum the perfect example of a superb FPGA video graphics card implementation. Paired with a real Z80 is a really nice machine.

 

My implementation for dual CPU was going to be a DMA system from the video Z80, a ROM with built in functions for it, and an IO space register bank for control.

 

FPGA is the system I'm thinking of going with since I need one for my sound chip anyways.

[Astal4]

 

Revision zero motherboards arrived!