exxos's Atari, Amiga & retro forum

Cwiiis wrote: 13 Oct 2023 11:09 Well, this may be indicative of some other issue that could be solved, but I've found that if I disconnect the MIDI cables, the issue goes away! They are quite long, I guess that interferes with things somehow? If anyone knows a fix that would allow me to keep the cables connected, I'm all ears...

Midi has opto isolates and buffers on it, so not sure how that can cause any issues with the ACIA.


Have you checked out singles like E-clock from the CPU to the ACIA ?

exxos wrote: 13 Oct 2023 11:23

Cwiiis wrote: 13 Oct 2023 11:09 Well, this may be indicative of some other issue that could be solved, but I've found that if I disconnect the MIDI cables, the issue goes away! They are quite long, I guess that interferes with things somehow? If anyone knows a fix that would allow me to keep the cables connected, I'm all ears...

Midi has opto isolates and buffers on it, so not sure how that can cause any issues with the ACIA.


Capture.PNG


Have you checked out singles like E-clock from the CPU to the ACIA ?

I've no idea what that even means, so no, afraid not :?

Cwiiis wrote: 13 Oct 2023 11:44 I've no idea what that even means, so no, afraid not :?

Scope pin 14 of the ACIA (E). It comes from the CPU. It's the Enable signal for the ACIA. If that's "bad" it may cause odd problems. Though that be a new fault to me if so. But knowing how screwy these machines are...

exxos wrote: 13 Oct 2023 11:23

Cwiiis wrote: 13 Oct 2023 11:09 Well, this may be indicative of some other issue that could be solved, but I've found that if I disconnect the MIDI cables, the issue goes away! They are quite long, I guess that interferes with things somehow? If anyone knows a fix that would allow me to keep the cables connected, I'm all ears...

Midi has opto isolates and buffers on it, so not sure how that can cause any issues with the ACIA.

I don't know that area of the ST series at all but IIRC the MIDI and keyboard share an interrupt. Can one 'drown out' the other?

BW

Badwolf wrote: 13 Oct 2023 12:31 I don't know that area of the ST series at all but IIRC the MIDI and keyboard share an interrupt. Can one 'drown out' the other?

It is certainly a interesting question as both the ACIA share the same datalines, CS and IRQ line. Like if the keyboard and midi interrupt happened at the same time which one would "win" :shrug:

Maybe @ijor can shed some light on it?

ah no there are 2 CS lines. So each ACIA is on its own address.


I don't know how TOS processes it interrupts though. Does not seem to be any way to know which chip issued the IRQ.

I can only assume TOS reads the KB one first, and if it gets back "11111111" it assumes no KB input, and further then assumes it is a MIDI IRQ :shrug:

exxos wrote: 13 Oct 2023 12:58 It is certainly a interesting question as both the ACIA share the same datalines, CS and IRQ line. Like if the keyboard and midi interrupt happened at the same time which one would "win" :shrug:

Maybe @ijor can shed some light on it?

Simultaneous interrupts shouldn't be a problem. Software, either TOS or a custom interrupt routine, should be able to deal with that. You can even have multiple simultaneous interrupts triggering on the same ACIA, like one transmit and one receive interrupt. Shouldn't be a problem.

exxos wrote: 13 Oct 2023 13:01 I don't know how TOS processes it interrupts though. Does not seem to be any way to know which chip issued the IRQ.
I can only assume TOS reads the KB one first, and if it gets back "11111111" it assumes no KB input, and further then assumes it is a MIDI IRQ :shrug:

Each ACIA has a status registers that indicates if any interrupt is pending, and if so, which ones.

So, an interesting discovery - recent Atari STE problems have me using the MiSTer instead so I don't just end up spending all my time debugging/fixing/breaking things - turns out this issue with MIDI killing inputs in some games happens on the MiSTer too! So whatever defect it is, it would appear to be software in nature (or something inherent to the hardware design?) and not specific to just my particular STEs. Bit annoying in that I have to fiddle with settings or physically unplug my midi board/cables to circumvent this, but very interesting that the behaviour isn't limited to just original hardware.

ijor wrote: 14 Oct 2023 16:17 Each ACIA has a status registers that indicates if any interrupt is pending, and if so, which ones.

What might happen if the higher priority interrupt is constantly firing? I'm thinking, for example, of severe noise on MIDI ports causing it to think its buffer is full?

(Completely hand-waving, I know)

BW