IBM PS/2

Wonder MCA Part 3 – Hunting a Ghost & How MADE24 broke /CMD on 386 PS/2 chassis

/ / IBM PS/2

A driver that “shouldn’t” work

For most of WonderMCA’s development the chassis matrix looked encouraging. The card came up clean on the IBM PS/2 Model 8550Z, on the 8555, on the 8556, on the 8557. POST passed, the option ROM checksum was correct, the screenpad lit up, the floppy emulator mounted images, the NE2000 tunnelled traffic over W5500. By early May 2026 four 286-class & 386 PS/2 boxes were green across the matrix.

Then I plugged the same card into a Model 8570 — the 25 MHz 386DX desktop — and got:

D0000  114

POST 114. The chassis BIOS had scanned for option ROMs in the C000–DFFF region, found WonderMCA’s 0x55 0xAA signature at segment D000, summed the declared 16 KB, and the modulo-256 result wasn’t zero. From the chassis’s point of view the option ROM was corrupt.

But it wasn’t corrupt. The 16 KB ROM image is built by … Read the rest

IBM PS/2

Wonder MCA part 2 – MEM & IO path working

/ / IBM PS/2

After several weeks of design work, I finally received the first WonderMCA prototype PCB. I’ve been using JLCPCB for months now, and they consistently deliver: the quality is excellent and the path from design to physical board is remarkably smooth.

The First Milestone: Four Basic Transfers

My first milestone was to get the WonderMCA (WM) handling the four fundamental MCA bus transfer types:

  • MEMR — Memory Read
  • MEMW — Memory Write
  • IOR — I/O Read
  • IOW — I/O Write

Per the MCA specification, these transfers are encoded on the bus as follows:

TransferM/IOS0S1
MEMR110
MEMW101
IOR010
IOW001

I started my experimentation on the PS/2 model 55 for no specific reason, and it was a good choice to start and I discover also very quickly the cliff in front of me.

Memory cycles (MEMR/MEMW) must complete … Read the rest

IBM PS/2

Wonder MCA Part 1 – the origin

/ / IBM PS/2

Introduction

After hesitating for months, I finally decided to start the WonderMCA project… It is just the beginning of a very long journey to bring MCA Bus based IBM Computer a software defined card like the famous #PICOMEM or the #PICOGUS.

This project has been in my head for many years, and I have postponed it way for too long.

I will be posting here my progress as I expect this journey to be more than a walk in the park… 

The story behind this project is pretty simple, it is all about frustration not being able to find MCA extension card available at a decent price. The lack of ongoing project was also a trigger.

What made me hesitate for so long was mainly: 

  • Scarce / or very little documentation,
  • Almost no open project, 
  • Lack of required skills,
  • Complexity of the MCA Beast

Over the last 2 years, … Read the rest

Experiment

Adding ESP32 WiFi Module to Raspberry Pico RP2040 / RP2350 CPU – Part 1

/ / Experiment

As I continue my journey building stuff based on Raspberry CPU, for one project I need to build a custom RP2350 board and to onboard on the PCB a WiFi Module.

Here is the source of the project on GitHub https://github.com/vibr77/ESP32C3_RP2350_WiFi

One could argue that using the recent release of the RM2 (existing on PICOW & PICO2W) would be the easiest solution. This is true, and the software integration (the driver) is also very mature and delivers very good performance.

The alternative approach is to consider module that would bring WiFi and Bluetooth supports. Many solutions on the market such as ATWINC1500 or the family of ESP32 products.

The key criterias for my projects are:

  • Form factor,
  • PCB integration capacity
  • Performance,
  • Maturity & openness,
  • Cost

For all these reasons, I have selected the ESP32C3-WROOM-02-N4 chip from expressif

On-board PCB antenna or external antenna connector

  • 2.4 GHz Wi-Fi (802.11b/g/n) and Bluetooth® 5
… Read the rest
HomeNetworking

Heating Opentherm Boiler & HomeAssistant, meet the FusionBerry, part 1

/ / HomeNetworking

This is the first post on this topic, and I wanted to share my lessons learned and also a project initiated a few month ago. The photo below is the first release of the FusionBerry up and running to manage an end to end open solution to manage Opentherm, Ethernet, MQTT, HomeAssistant boiler & heating solution.

It integrate perfectly with node red flows to fully manage the cycle (scheduler, TRV management, boiler order), but this will be another post soon.

The problem statement was how to manage, automate and optimize the heating system in my house with Home Assistant, opentherm boiler and multiple TRVs.

I spent hours to find the right approach, that brings efficiency, reliability and easy operation. I have tested many products on the market (netatmo, Legrand, deltadore). All excellent product, but sometimes blackbox, not open and flexible as I needed and also not addressing opentherm.

The main … Read the rest

AppleII, SmartdiskII

Logic Analyzer & Apple II

/ / AppleII, SmartdiskII

Over the last few weeks, I have built several SmartDisk II, and I have been testing the hardware and the latest firmware release on my beloved IIGS.

The IIGS is very easy to work with, and loading GSOS 6.04 immediately reveals any timing issues.

Everything was fine until I received a message from a user explaining that some SmartDisks were working on the IIc Smartport and others were not, though all were working on the IIGS. 

I decided to sort this out, so I took all my 10 samples—and guess what? Half of them were not working on the IIc.

Finding the issue was like looking for a needle in a haystack, as the problem was not consistent.

I gathered my courage and reopened the engine. I spent endless hours trying to figure out what was not working.

I used my preferred logic analyzer, and for some reason the incoming … Read the rest

IBM PS/2

Resurrecting an IBM 8540 PSU

/ / IBM PS/2

I finally was able to find an IBM PS/2 8540SX in a good esthetic shape with no plastic issue and all the very specific IBM screw on the back. The 8540 was one of the last (with the 8535) to be equipped with ISA bus and not the proprietary Micro Channel bus MCA. The is why, it is been highly chased by retro hunter.

In this case, this IBM was sold as not working and as it arrived the initial testing was not showing any sign of life.

The demand on this kind of computer is extremely high and almost with no offer at all, so when you see one appearing on the market one does not hesitate too long. The seller, was king enough to make the packaging strong to avoid any damages, especially on the plastic corners.

I was betting on the non starting root cause to be … Read the rest

AppleII, SmartdiskII, Uncategorized

SmartDisk II – The Origin

/ / AppleII, SmartdiskII, Uncategorized

I remember the first time I had my first prototype of what will become the SmartDisk II loading the NIB image of BoulderDash II on my Apple II.

The first prototype was made on a very poor quality breadboard with a STM32 Bluepill, with a lot of ICs. The process to load NIB image was not really accurate, but I was so proud of having at least something working. 

This was the beginning of my journey to design and build an accurate Apple II Disk Emulator. I reached out to the Applefritter community for help on this project, and I received more than what I was hopping. This was a few month of long hardworking and debugging session with a lot of up and down along this way.

The purpose of this project was really a personal goal to experiment, learn, understand, and build. My approach from the beginning was … Read the rest

AppleII, SmartdiskII

Smartloader for SmartDisk

/ / AppleII, SmartdiskII

I received a message on AppleFritter to add a new feature on the SmartDisk II. The request was to have the content of the SDCard to be displayed on the Apple II at startup like Slot card are able to do it. I did not reply straight because I was not sure it was possible or not. 

I started reflecting on how I would do it given my knowledge of the DISK II interface card and also the way the SmartDisk II is working. I had an interesting discussion with Antoine Vignau on an approach that would use the SMARTPORT protocol with undocumented function around CMD. With this approach the SmartDisk II would issue a SmartPort CMD with specific parameters that are not used by the SmartPort ROM or the SP6 Rom. I still think this is possible, however the approach would assume that the Apple II has a SMARTPORT … Read the rest

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