145 lines
3.4 KiB
Markdown
145 lines
3.4 KiB
Markdown
Technical Notes
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===============
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It took me a lot of time digging around the Internet to find some of this stuff.
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I'm writing down the highlights here,
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so that when original sources fall off the net,
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hopefully at least my notes will still be around.
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Sample Rate
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-----------
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The number of samples taken since the last HID report
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is sent as the second Y axis.
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If you `#define DEBUG`,
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you can use the
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[included gamepad tester](gamepad.html),
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to see the approximate number of samples as an integer,
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on the first X axis.
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This is approximate,
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because the browser encodes the value as a real number between -1 and 1.
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We convert it back, but may lose a little precision.
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It's close enough for me,
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hopefully it's close enough for you.
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Debouncing
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----------
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Using `millis()` time to debounce the switch
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roughly halved my sample frequency.
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So instead, I do some preprocessor arithmetic
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to calculate how many samples to take after an edge,
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in order to debounce switches.
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The drum controller was a partcular pain:
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in addition to the switch bouncing,
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the stick was bouncing on the rubber pad.
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I settled on a 40ms silence window as feeling pretty good.
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You can adjust this if you want to.
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USB Junk
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========
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Gamepad Buttons
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---------------
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The `buttons` struct member is a bitmap,
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each bit mapping to one of the 12 buttons reported through HID.
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Here's what each bit means:
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* 0o00: Blue
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* 0o01: Green
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* 0o02: Red
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* 0o03: Yellow
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* 0o04: Orange
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* 0o05: Tilt Switch / 2x kick
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* 0o06: Solo modifier (second row of buttons on guitar)
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* 0o07: ???
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* 0o10: Minus
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* 0o11: Plus
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* 0o12: Drum pad modifier
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* 0o13: Cymbal modifier
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* 0o14: Select
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hatAndConstant
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--------------
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The HAT switch reports its position like a clock.
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7 0 1
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6 8 2
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5 4 3
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0 is up,
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2 is right,
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4 is down,
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6 is left,
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and 8 is centered.
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velocity
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--------
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I don't know how I can verify that I'm setting this right,
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but the `rbdrum2midi` program looks at these bytes to detect hits.
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I set them to 127 when a hit is detected on the digital pin.
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Sending these values does not seem to cause problems with my Wii games.
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Product ID (PID)
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----------------
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Nicholas,
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who did the initial work on the guitar,
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suggested that PID 0x0005 would get the sketch working as drums.
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And that was correct:
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this works great on
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Wii Rock Band 1 and
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Wii LEGO Rock Band.
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But it fails in frustrating ways on
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Wii Rock Band 3:
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the yellow and blue pads don't navigate menus,
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and cymbals aren't detected.
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The fix was setting the USB PID to 0x3110.
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Drum Velocity
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--------
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I split the 12 "reserved" bytes from Nicholas's
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`struct InstrumentButtonState`
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into 4 bytes of I-Don't-Know, 4 bytes of velocity,
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and 4 more bytes of I-Don't-Know.
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Whenever a pad is hit,
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I send 127 on the corresponding velocity.
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I did this because a program called `rbdrum2midi`
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ignores the button press events,
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and looks only at the velocity values.
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None of the Wii games I have
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seem to care what these values are set to.
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References
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=========
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The most valuable sources of information I found were:
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* [Nicholas Angle's reverse-engineering write-up](https://www.niangames.com/articles/reverse-engineering-rockband-guitar-controllers)
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* [Nicholas Angle's guitar controller program](https://github.com/NianZo/WiiGuitarController)
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* [Clone Hero Wiki: Drum Mapping Guide](https://wiki.clonehero.net/books/guitars-drums-controllers/page/drum-mapping-guide)
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* [rbdrum2midi source code](https://github.com/rbdrum2midi/rbdrum2midi)
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