[Coco] More coco music on the web

[Torsten Dittel]

Bill Pierce via Coco <coco at ...> writes:

> If you ever do drag up that Coco 2 software, I'd love to see it.
Especially the sources on how you accessed
> midi.

My journey into CoCo MIDI programming started indeed with LYRA and my Dad's
early Coco 1. First we figured out that an op-amp at the CoCo1's bitbanger
was much too slow for more than 9.6kB transmissions (we exchanged that
discrete part by a faster one, I had a discussion on that one here with Gene
about a year ago). When it principally worked like on my CoCo2B, I noticed I
had "hangig" MIDI notes on my MDI synth from time to time (it looked like
the "Note Off" was missing). I started to disassemble and debug LYRA when I
found that it was sending the corresponding MIDI event, but the transmission
was disturbed. Having then a closer look at Lester's bit banger routine, I
was able to find and patch a bug I've already described here a few years ago
( http://comments.gmane.org/gmane.comp.hardware.tandy.coco/21822 ):

"[...] the ML-code [...] was trying to send the bits in 28.5 (=57/2) cycles
by sending the "0"s in 28 and the "1"s in 29 cycles [or vice versa]. This
worked only perfect in cases like $55 or $AA. I wrote a new routine which
was transmitting the first bit in 28, the second in 29, the third in 28
cyles and so on. I later used the code in some of my own (never released)
MIDI programs until I had my selfmade 2 ACIA MIDI Pak (2x MIDI in and out)
[...]"

Regards,
Torsten