Hi Lawrence,

Yes, I’ve written the AVR code in ATMEL Studio. Every 1/100 of a second the routine scans the matrix. It provides a press scan code or a release scan code. It generates an interrupt for the VIA on key changes.

I think the code is not very nice, but it works for me.

Thanks for the nice compliments. I finished this project a while back. Programing for it would be a logical next step, but I also feel the urge to simplify and improve on the hardware.

OK folks, I hope I have a project here to distract you from reality. :P

Ten years ago I started gaining up on electronics and joined Forum64. Seven years ago I joined this forum with the intention of creating my own (gaming) computer with hopefully better specifications than the Commodore 64 ...

01 20191103_121916.jpg
02 20191103_114540.jpg
03 20191103_114923.jpg
04 300front.jpg
05 1.png
06 20181220_210428.jpg
07 20191103_113904.jpg
08 20191103_113945.jpg
09 20191103_114100.jpg
10 20181220_193358.jpg
11 20181220_210128.jpg
12 20181122_124636.jpg
13 20181122_122301 ...

I’d like to thank those who have written (here and by post). I’m a few weeks at home now and I’m recovering well. Getting off of the painkillers is probably the most difficult at the moment.

I’m busy with old and new projects, all 6502 and AVR related.

Of course I wish that everyone stays well or ...

@Chromatix
Perhaps you could upload the code as it presently stands Sure thing:
Player31 bugfix working version.asm
I recall previously you said the tempo didn't vary with CPU speed The difference is more noticeable with the MIDI file I’m using now. (from Duke3d) So I’m not so sure anymore if ...

@Chromatix
Thank you! It’s working now, that is, the MIDI file is playing back as previously. All events are being send, but there where’re multiple events with delta time 0, it starts stalling. i.e. the player behaves as if there were no software buffer or transmitter interrupt. :(
I’m not sure if ...

@Chromatix
I suspect he's trying to learn by doing, rather than by following a recipe. Indeed I am. I just began writing this MIDI player by reading the MIDI implementation. It worked out very quickly and very well, but I must admit that I have a hard time to make sense of what happens when the ...

OK, this is the interrupt code:

I’ve also appended the whole source, it’s too long to put it in the post.

interrupt
pha
phx
phy

lda isr
and #%00001000 ;check if interrupt is caused by C/T
beq HandleUart ;no? goto uart irq
HandleTimer
lda tc ;is binvlq = tc?
cmp binvlq
bne IncTc ;no ...

Well that took me some effort! First I replaced the SC26C92 with the SC28L92. In order to make use of the 16 bit FIFO, I had to enable it by setting the MR0A[3] bit to ‘1’. This made no difference in playback performance.

Then I implemented a circular 256 byte software buffer together with ...

@Chromatix
I’ve got the version SC26C92 with 8-byte FIFO in use, but I also got one with 16-byte FIFO. So those buffers are used automatically? I could do two quick checks, one is to replace the SC26C92 with the SC28L92. That should at least be noticeable. Secondly I could indeed check if the buffer ...

I think I know what's going on here. You say the behavior doesn't depend on CPU clock speed, but there's another clock that you're not varying - the baud rate of the MIDI interface. Granted, that is set by the standard, but I think that's what you're running into. I’m sure you might be right about ...

I think my MIDI player works pretty well, all be it only for MIDI type 0 files. But that’s ok, because I can convert virtually any MIDI file to type 0. The only problem I have is when I play a MIDI file with a lot of information (delta time 0 and or running status), I get audible slowdowns.

To ...

Thanks! I'll most likely need that in the future.

Happy and healthy 2019 to all of you!

I finally created a universal 24x16 bit multiplication and a 40/40 bit division routine. They are not optimized for speed or size, but they are as readable as possible.
mul 24 by 16 bit no zp.asm
div 40 by 40 bit no zp.asm

I also tackled your (Chromatix’s ...