Pi Compute Module

So my idea is to use the middle line of the connector to pass specific signals from the Broadcom CPU, to open the way for designing new cards…

Did you read the PDF I linked you to? Later (RiscPC era) cards use the middle row of pins. Plus the podules run at 5V logic and modern stuff at 3.3V… [and in some cases like parts of the Beagle, 1.8V!]
If it’s only ever going to be used by you then you might be okay, but the moment you plug in a podule that supports DEBI and it pumps 5V signals into your Pi……

but why i understand that the ARC had a IOC, an MEMC, a VIDC

IOC – I/O chip, sort of Acorn’s version of a combined Northbridge/Southbridge.
MEMC – memory controller, the MMU.
VIDC – the GPU.

Pretty standard parts of a computer system. If you split the IOC up into different parts, then one could say the 6522s and µPD7002 are this on the Beeb, the MEMC is a lot of 74-series logic, and the video ULA/SAA5050/6845 are the GPU (really stretching the definition of “GPU”!).

underestimate de capabilities of the Broadcom chip who has also a lot of integrated capabilities…

Yup. Pretty standard fare for FHD-era media player devices: ARM core (that’s subservient to the GPU!), the GPU, MMUs, USB, SPIx3, IICx2, UARTx1½, DMA, GPIO, timers, SD interface, PCM/I2S audio, PWM… The Pi adds a heap of memory, Ethernet, and a USB hub.

As for MIDI, I created a module that has more or less the same API as the old Acorn one (basically because Maestro is the only music software I have), and Dave has picked it up to add many improvements and enhancements.

I should add that one aspect of my work is that the USB MIDI module’s API has moved even closer to the Acorn one in that the USB MIDI module now supports 4 ports (i.e. devices), same as Acorn.

The compute module has 45 lines available to do the task of connecting a simple podule (without B pins), 2,4,8 Mhz will be produced by an external oscillator on the interface board along with the necessary 74LVC245 to make the level transitions.

If you use a podule that requires the bus signals to be synchronous with one of the clock signals, you will find that it will occasionally malfunction because of metastability. It’s an extremely difficult problem to solve.

oops, there was a typo in one of my comments, it’s not 45 but 54 GPIO’s that the compute module make available, but it is not sufficient for a full ‘IONYX’ podule connector implementation, that’s why i stick to a simple ARC (64 pins) podule interface with some enhancement in the middle row pins…(e.g. one of the GPIO’s will be used to toggle full backplane on/off of the bus, this will allow me to run other OS’s without risking to corrupt something attached to the backplane…)

i already purchased this board for evaluation purposes: https://www.waveshare.com/compute-module-io-board-plus.htm, it is for me a good candidate to interface to the backplane…

Replying lately to Dave, I worked several years ago in a company that developed a podule for doing electro-encephalography, after AKA10, it was also in my list of interfaces to implement… But mostly, let’s admit it, it’s also mainly for playing with electronic and see ‘if it can be done’…

electro-encephalography

How do you pick that up and turn it into a useable signal?
I’ve tried poking my head and chest with the oscilloscope¹ probes (both the circuit test one and the banana plugs one) and at it’s most sensitive (something like 5mV/div) all I can see is the induced mains hum that turns up in everything.
I’m not sure I’d be able to make any sense out of what’s going on in my head ², but it would be kind of cool to visualise my heartbeat at least.

¹ The battery powered DSO Shell, not the big cathode ray thing.

² Back in the early 80s, child psychologists tried and failed… ;)

I’ve tried poking my head and chest with the oscilloscope1 probes (both the circuit test one and the banana plugs one) and at it’s most sensitive (something like 5mV/div) all I can see is the induced mains hum that turns up in everything.

From 20+ year old memory, the normal setup uses a floating front end¹ pickup feeding signals into differential amplifiers such that the noise signal on the pair of inputs is fed antiphase to the diff amp and the difference is the required signal.
Googling (duckducking ??) for circuit diagrams comes up with many items including this one

If you try without a differential input, you lose all the useful stuff in the noise, as you’ve discovered.

¹ Power for the front end is dc isolated from the backend amps. Basically, a PSU fail in the non-isolated circuitry isn’t going to put interesting voltages into places you might live to regret.

Basically, a PSU fail in the non-isolated circuitry isn’t going to put interesting voltages into places you might live to regret.

Or worse, you might not live to regret.

It would be kind of cool to visualise my heartbeat at least.

I’ve seen more than enough traces of my heartbeat. I’ve heard cardiologists commenting on it more than enough, too. Whether its peculiarities have anything to do with interesting voltages I put through myself in my youth, who knows?

From 20+ year old memory

Doing some rummaging, it looks like you can get modules based upon the AD8232 that does all of this automatically. Though, of course, it seems as if most of the ones listed on Amazon are cheap Chinese knockoffs that only work when you solder in a rather important resistor that was omitted.

That’s for heart monitoring.

isn’t going to put interesting voltages into places you might live to regret.

That’s why I only tried with the battery scope. Even if running it from a power adaptor, there are no “interesting voltages” anywhere near the equipment, and certainly nowhere near important parts of me.

Or worse, you might not live to regret.

The only thing I’d regret is that I have no friends and no social life and nobody here really knows me. I’m okay with that, I’ve always been a loner. But the regret is that nobody will think to write a snarky comment like “What a stupid way to die” (“Quelle façon stupide de mourir”) on my grave. That would be tragic.