Autonegotiation @ MiSTer

[dtimber]

Hi,

when using the MT32 pi in combination with a MiSTer, is there some sort of autonegotiation for the RX and TX pins of the USB connector?

I'm just wondering because the MT32 pi HAT and the MT32 pi lite using the same pinout. Shouldn't the pinout for MT32 lite be swapped because the USB cable on MT 32 pi HAT also has the TX and RX pins swapped?

[dwhinham]

...is there some sort of autonegotiation for the RX and TX pins of the USB connector?

Yes. This is because some A-A USB cables are not crossed over, so MiSTer has to handle both cases.

https://github.com/MiSTer-devel/Template_MiSTer/blob/master/sys/mt32pi.sv#L88-L94

[dtimber]

Thank you for the quick reply and the clarification.

[venice1200]

Hi,
the MiSTer Pinout Schema in the Wiki is for the usage of „crossed“ USB A-A cables?
If so, Pin 9 of the MiSTer SNAC Port is needed for 1:1 Cables or the MT32-pi lite.
Is this correct?

All the best

[dwhinham]

Pinout is crossed because USB spec says the cables are supposed to be crossed. The wiki pinout assumes you are using a cable, like the original non-lite mt32-pi HAT.

Pin 9 is not currently used by mt32-pi but it could be in the future (e.g. routing MIDI into MiSTer running a sequencer for recording a performance).

I have not compared the lite schematic with the non-lite; I did not design it, so any questions about it should be directed to Sorgelig.

Is there some kind of problem?

[venice1200]

Many Thx to your reply.

The IOBoard v5.6 (and v5.5) has VCC (3.3v) at Pin 9 of the SNAC Port.
The newer Boards (Analog 6.1/Digital 1.2) have a jumper to choose the usage of another IO Pin or VCC there.
Mostly the additional IO is the default setting.

This means you need to add the additional IO Pin to your v5.6 Board if you use an 1:1 cable or if you want to use an MT32-pi lite.
Modding the v5.5 Board need more work than adding the IO Pin.

There was an entry in the MiSTer Forum
https://misterfpga.org/viewtopic.php?p=46042#p46042
and it looks like that the manual IO mod fixed the problem.

dtimber will test an MT32-pi lite Board next week with an un-modded IOBoard v5.6 to if what to do to get it working.

And many many Thx for your MT32-pi System.

[dwhinham]

I understand now, thanks.

If dtimber can verify the steps necessary to fix the older I/O board, I'd welcome any improvements to the documentation so that others know what to do in this situation.

Thanks for appreciating mt32-pi, and also for your work on tty2oled. Unfortunately I haven't found time to try it myself, but it looks very cool and I know people like your project a lot. 🙂

[venice1200]

Some more Infos!
The Standard "lite" Version of the MT32-pi uses a 1:1 connection by plugging the MT32-Board directly in the MiSTer's SNAC Port.
This connection needs an IO-Board >= 6.1/1.2 or a manually modded IO Board v5.6 with the additional IO6 connection
as the MiSTer crosses the lines internally and USB Pin9 (IO6) which is normally midi_rx becomes USB Pin6 which is is2_bclk.

dtimer has built his own "lite" board and he was able to use his 5.6 IOBoard without modification
but he had to change his board pins in that way that it looks to the MiSTer like an "normal" MT32 with crossed USB cable.

[venice1200]

Maybe the right words for your wiki:

The MT32-pi lite need one of the newer IO Boards 6.1/1.2 and need the 3.3/IO Jumper set to IO.

The normal MT32-pi, which is normally connected with an USB A-A cable (RX/TX crossed), can be used up from IO Board 5.6.

[dwhinham]

Thanks for the extra info.

I will be receiving a "lite" soon and I have a MiSTer here with a 6.0 board for testing.
Will hopefully find time to update the wiki soon when I can test everything here.

Cheers,
-Dale