PicoCPC

Rodrik Studio announced its PicoCPC expansion card, which is created with the help of FreddyV (the author of the PicoMEM ISA card for IBM PC).

Architecture

The PicoCPC use a Pico2, connected via multiplexor. This let enough pin to add an I2S DAC, MicroSD and some more control signals. The Final board will be really different, with RP2350B Directly soldered.

No 5V pin go to the pico. We use some 1 buffer, 1 level shifter, 3 multiplexers. We write to the CPC with 3.3V, we use 5V to the CPC only to drive some signal like A15 for C3 memory mode and IOReq to disable intern floppy.

We prefer to have somerthing between the Pico and the CPC, as even if 5V work now, there is no guarantee that the boards will work after some years of intensive usage. It is really better to be carefull.

The board can decode any I/O port and of course RAM/ROM cycles. As it use a Pico2, its RAM is doubled vs Pico1 and it can access a 8MB PSRAM as well.

The PicoCPC does NOT use a CH376 chip, everything is done with the Pico itself. PicoCPC handles FAT12, 16, 32, ExtFS. CH376 will be emulated on the board, with nothing to do at the CPC side.

There is no external ROM, so the microntroller access the emulated RAM/ROM and USB/MicroSD at the same time: Direct write from the uSD to the CPC emulated RAM at 3MB/s (For example).

The PicoCPC is clocked at 366Mhz. So it is not as powerful as the RSF3 clocked at 480Mhz. But it is more powerful than the M4 Board clocked at 168Mhz. Source

Multiplexers

The "Secret" of the PicoMEM/PicoCPC is its multiplexers. Source It allow to limint the number of I/O needed and act as a Voltage converter at the same time.

The Pi Pico allow to have multiple PIO core, plus the main core working together in parallel,so the PIO manage the Multiplexer, reconstruct the Address, while CPU core detect and manage the Control signals, Read in advance the High part of the address to jupt to the correct code. (IO MEM Read or Write, Bank number) So, when the Main core is in the correct code section, it can read directly the full Address from the PIO.

The PicoCPC use only 12 I/O to manage all the address, Data and Control signals. We can add 2 pin only to control the multiplexer. Then, the CPC bus is "manipulated" Via ROMDIS, RAMDIS, RD, A15, IOREQ (Pico Output)

With this way to do, it is possible to be almost as fast with multiplexing that without.

Features

It now has :

• ROM Emulation
• RAM Emulation (464/6128), all modes, except C3 mode for now
• Floppy disk controller emulation, supporting .DSK and even most of the copy protected games. (on 464)
• Create Floppy "pack" and swap between them with a button
• Navigate in the SD and run games from it
• Setup program helping to do the initial config if there is no config file on the SD (With graphics and music)
• Various commands, to list and load the ROM and Disk images
• Reset button

C3 mode to arrive in the next hardware release (update 09/04/2025: C3 mode works perfectly fine). And much more for the final hardware release: vocal synthesizer, cpr cartridges, usb mouse, wifi, nfc, ...

News

Here’s the translation into English of the description of the 07/03/2025 video:

It’s still far from being finished, but it’s progressing well.

What’s still missing:
*Loading and unloading ROMs from BASIC
*Copying files between SD and floppy disk
*Saving files to SD (for now, the Pico can only read and launch)
*Formatting floppy disks
*Displays on the I2C screen during the Wizard
*All the sound part
*All the Wi-Fi part
*All the NFC part

Prototype 2 will require a major change on the I/O side but should normally open up more possibilities, like the C3 memory mode on 464/664, switching to 512KB of extended memory, and sound.

At the moment, I’m aiming for June as a tentative date. Even if the code isn’t finished, the hardware should be.

In the comments of that video, Rodrik said:

• "When it works on all CPCs, including the Plus models, and the hardware is more or less final, I’m aiming for June."
• "The features will evolve; I wrote that in the description. The next big thing will be sound—voice synthesizer—but also a second AY chip and maybe some other quirky stuff like Adlib. Then Wi-Fi and NFC."
• "I plan to add Wi-Fi later if possible, and also USB, which is simpler than micro SD for transferring things."
• "I can even say it’s very likely that Plus cartridges will be emulated soon."
• "Wi-Fi is planned for the longer term; the separate Wi-Fi module for Pico2 isn’t available yet."
• "There are too many boards, often too expensive, hard to find, and with different features. The idea is that the PicoCPC should cost half the price of a DDI5."
• "I didn't check the price of DDI-5, but this one will be around 70€."
• "I will have a distributor in UK, so no problem."
• "When the board is ready, I will open-source both ROMs, the PicoCPC and the Wizard."
• "It’s coming along, but it’ll take a few more months. The final board will be pretty high-tech with 4 layers, etc., and some surprises like connectivity features."
• "There will be a case around it to make it look like a peripheral from back in the day."
• "The HDD part isn’t great; binaries that load other binaries won’t work. In the end, I could only put a few games on it."

On 12/04/2025, Rodrik posted on CPCwiki forum:

I wanted to clarify few things, there is no interest list, nowhere to register to. When the card is ready enough, it will be made available via resellers in France, UK and maybe US.
I still don't know when this will happen, the card did progress of lot since the start in December last year, this means 4 months ago. But I think 3 more months at least are required to make it work properly on all CPC flavors.

The card is currently limited by the RB2350, I do not have enough gpio, so I either use an oled screen, either I2S DAC, either use the pins to drive some signals on the bus. So it requires a new revision with e 2350B soldered on board.

Feature list is unknown yet, but it will grow over time. The card will be available with lot of hardware, but only future firmware revision may make use of it.

Links

• PicoCPC project presentation - 16/01/2025
• PicoCPC project update - 07/03/2025
• Topic on CPCwiki forum