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API Notes

Basics

The o_C firmware operates with several "concurrent" threads. (really they interrupt each other I guess)

There is a main loop as well as an ISR that fires from a timer. The loop acts as a watchdog while the ISR does all the work. UI events are on a seperate ISR timer. The display driver and input polling are also on independent interrupts. So that's at least 4? separate processes happening in a cascade for every cycle, which is 60us (nanoseconds) or 16.666khz

That's the general idea.

Anyway, we have top-level Apps and then there are Applets as implemented in the Hemisphere App. An Applet inherits the base class HemisphereApplet and gains the superpowers necessary to live on half of your module's screen.

Base Classes

The two primary interfaces in the Hemisphere API are HSApplication and HemisphereApplet. They both have many similarly named methods for I/O and graphics, with HemisphereApplet taking extra considerations for offsetting both in the right side.

All of the hardware details are neatly abstracted under these two interfaces. If you simply want to make an applet that does some stuff, these APIs are your starting point.

Applets

There are a few different things an Applet must do:

  • Controller - the main logic computed every tick (every time the ISR fires)
  • View - draw the pixels on the screen (there are many helpful gfx* functions)
  • UI Event Handling:
    • OnButtonPress - what to do when the encoder button is pressed
    • OnEncoderMove - what to do when the encoder rotated
  • OnDataRequest / OnDataReceive - how to save / load state

There is also a Start() function for initializing things at runtime, plus some Help text. That's about it.

You can easily try it out by copying the HEM_Boilerplate.ino.txt file into place, and then adding your computations to its skeleton.

Applet Functions

Function? or Method? Either way, this is how you do the things.

I/O Functions

The main argument of each is the channel to operate on - each half of the screen gets 2 channels. So n is typically either 0 or 1.

Input:

  • Clock(n) - has the digital input received a new clock pulse?
  • Gate(n) - is the digital input held high?
  • In(n) - Raw value of the CV input
  • DetentedIn(n) - this one reads 0 until it's past a threshold ~ a quartertone

Output:

  • ClockOut(n) - hold the output high for a pulse length
  • GateOut(n, on_off) - set the output high or low
  • Out(n, raw) - set the output to an explicit value

I've added a standard case function for modulating a parameter with a certain input.

  • Modulate(param, n, min, max) - automatically scales the input and modifies param

gfx Functions

There are many strategies for drawing things on the screen, and therefore, many graphics related functions. You can see them for yourself in HemisphereApplet.h All of them typically take x and y coordinates for the first two arguments, followed by width and height, or another x,y pair. x is how many pixels from the left edge of the screen. y is how many pixels from the top edge of the screen.

Some essentials: gfxPrint, gfxPixel, gfxLine, gfxCursor, gfxFrame, gfxBitmap, gfxInvert