SugiKit

Patch data model and System Exclusive message parser generator for the Kawai K4 digital synthesizer.

Implementation notes

Helper types

The System Exclusive messages deal in bytes and byte arrays. To make it explicit and to avoid typing, the following typealias definitions are used:

public typealias Byte = UInt8
public typealias ByteArray = [Byte]

Enumerated types

Many of the synth parameter values are modeled with enumerated types. To make the parsing of System Exclusive messages easier the types have an optional initializer that takes an integer value representing the corresponding byte from SysEx. For example, the LFO.Shape type has:

init?(index: Int) {
    switch index {
    case 0: self = .triangle
    case 1: self = .sawtooth
    case 2: self = .square
    case 3: self = .random
    default: return nil
    }
}

If the value passed in represents a valid enumeration case, it is used for initializing the object. Otherwise nil is returned.

To make generating SysEx messages easier, these enumerated types conform to the CaseIterable protocol which has been extended with a method that returns the index of the enumeration value:

extension CaseIterable where Self: Equatable {
    var index: Self.AllCases.Index? {
        return Self.allCases.firstIndex { self == $0 }
    }
}

Why this instead of rawValue? Can't remember.

Generating System Exclusive messages

Most synth blocks have a computed property data that provides the raw bytes needed for the generated System Exclusive message. It returns the bytes in the required format as a ByteArray.

The actual SysEx message is constructed using the computed property systemExclusiveData, which collects the bytes using the data property and adds the checksum:

public var systemExclusiveData: ByteArray {
    var buf = ByteArray()
    let d = self.data
    buf.append(contentsOf: d)
    buf.append(checksum(bytes: d))
    return buf
}