Add ESP32 PWMOutput support

Package.swift

@@ -13,13 +13,14 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/uraimo/SwiftyGPIO.git", from: "1.2.5"),
+        .package(url: "https://vato.ddns.net/gitlab/vato007/SwiftSerial.git", .branch("master"))
     ],
     targets: [
         // Targets are the basic building blocks of a package. A target can define a module or a test suite.
         // Targets can depend on other targets in this package, and on products in packages which this package depends on.
         .target(
             name: "Swift2dCar",
-            dependencies: ["SwiftyGPIO"]),
+            dependencies: ["SwiftyGPIO", "SwiftSerial"]),
         .testTarget(
             name: "Swift2dCarTests",
             dependencies: ["Swift2dCar"]),

Sources/Swift2dCar/Esp32ServoOutput.swift

@@ -0,0 +1,85 @@
+//
+//  Esp32ServoOutput.swift
+//
+//
+//  Created by Michael Pivato on 9/9/20.
+//
+
+import Foundation
+import SwiftyGPIO
+import SwiftSerial
+
+/**
+ This class implements PWMOutput from the SwiftyGPIO package to communicate over Serial with an ESP32 that is running
+ the sketch found in the esp32 subproject in picar: https://vato.ddns.net/gitlab/vato007/picar
+ */
+public class Esp32ServoOutput : PWMOutput {
+    private let serialPort: SerialPort
+    private let channel: UInt8
+    private let pin: UInt8
+    
+    public static let ESP32_RESOLUTION: UInt8 = 8
+    
+    public init?(forChannel channel: UInt8, forPin pin: UInt8, onPort port: SerialPort) {
+        if channel < 0 || channel > 16 {
+            return nil
+        }
+        self.channel = channel
+        // TODO: Add checks for pin number, or make init private with enums for each pin.
+        self.pin = pin
+        self.serialPort = port
+    }
+    
+    public convenience init?(forChannel channel: UInt8, forPin pin: UInt8, onPort port: String) {
+        self.init(forChannel: channel, forPin: pin, onPort: SerialPort(path: port))
+    }
+    
+    public func initPWM() {
+        do {
+            try serialPort.openPort()
+            serialPort.setSettings(receiveRate: .baud115200, transmitRate: .baud115200, minimumBytesToRead: 1)
+            let bytesWritten = try serialPort.writeData(Data([0, 1, channel, pin]))
+            if bytesWritten != 4 {
+                print("Wrote %d bytes, but should have written 4",  bytesWritten)
+            }
+            
+        } catch {
+            print("Failed to init PWM")
+        }
+    }
+    
+    public func startPWM(period ns: Int, duty percent: Float) {
+        do {
+            // Scale to 1 byte range, which is the current resolution.
+            let bytesWritten = try serialPort.writeData(Data([channel, (UInt8)((percent / 100) * pow(2, Float(Esp32ServoOutput.ESP32_RESOLUTION)))]))
+            if bytesWritten != 2 {
+                print("Wrote %d bytes, but should have written 2", bytesWritten)
+            }
+        } catch {
+            print("Failed to start PWM")
+        }
+    }
+    
+    public func stopPWM() {
+        
+    }
+    
+    // Patterns not supported for now.
+    public func initPWMPattern(bytes count: Int, at frequency: Int, with resetDelay: Int, dutyzero: Int, dutyone: Int) {
+        
+    }
+    
+    public func sendDataWithPattern(values: [UInt8]) {
+        
+    }
+    
+    public func waitOnSendData() {
+        
+    }
+    
+    public func cleanupPattern() {
+        
+    }
+    
+    
+}

Sources/Swift2dCar/Servo.swift

@@ -92,7 +92,7 @@ open class PWMHardwareServo : Servo{
         self.device = pin
         self.device.initPWM()
         self.internalValue = initialValue
-        self.device.startPWM(period: Int(self.frameWidth), duty: self.minDc + self.dcRange * ((internalValue - self.minValue) / self.valueRange) * 100)
+        self.value = initialValue
     }
     
     public func min(){