PWM Support (requires latest, unreleased t2-firmware)

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

lib/tessel.js

@@ -21,7 +21,7 @@ var modes = Object.freeze({
   OUTPUT: 1,
   ANALOG: 2,
   PWM: 3,
-  // SERVO: 4,
+  SERVO: 4,
   I2C: 6,
 });
 
@@ -35,17 +35,17 @@ var pinModes = [
   { modes: [0, 1 ] },
   { modes: [0, 1 ] },
   { modes: [0, 1, 2 ], analogChannel: 0 },
-  { modes: [0, 1 ] },
-  { modes: [0, 1 ] },
+  { modes: [0, 1, 3, 4, ] },
+  { modes: [0, 1, 3, 4, ] },
   { modes: [0, 1, 2 ], analogChannel: 1 },
   // Port B
   { modes: [0, 1, 2 , 6], analogChannel: 2 },
   { modes: [0, 1, 2 , 6], analogChannel: 3 },
   { modes: [0, 1, 2 ], analogChannel: 4 },
   { modes: [0, 1, 2 ], analogChannel: 5 },
   { modes: [0, 1, 2 ], analogChannel: 6 },
-  { modes: [0, 1, 2 ], analogChannel: 7 },
-  { modes: [0, 1, 2 ], analogChannel: 8 },
+  { modes: [0, 1, 2, 3, 4, ], analogChannel: 7 },
+  { modes: [0, 1, 2, 3, 4, ], analogChannel: 8 },
   { modes: [0, 1, 2, 3 ], analogChannel: 9 },
 ];
 
@@ -115,7 +115,7 @@ function ToI2CBusPort(value) {
   return undefined;
 }
 
-var samplingInterval = 0;
+var samplingInterval = 5;
 
 function read() {
   if (read.interval) {
@@ -137,8 +137,6 @@ function read() {
   }, samplingInterval);
 }
 
-samplingInterval = 10;
-
 function processRead(board, report, value) {
   value = +value;
 
@@ -190,7 +188,7 @@ function Pin(options) {
   var state = {
     isAnalog: false,
     pin: pin,
-    index: pin.pin,
+    index: (options.port === "B" ? 8 : 0) + pin.pin,
     mode: 0
   };
 
@@ -222,14 +220,15 @@ function Pin(options) {
           pin.input();
         }
 
-        if (value === 1 || value === 3) {
+        if (value === 1 || value === 3 || value === 4) {
           // TODO: Make sure this doesn't
           // interfere with pwmWrite
           pin.output();
         }
 
-        state.isPwm = value === 3;
         state.isAnalog = value === 2;
+        state.isPwm = value === 3 || value === 4;
+        state.isServo = value === 4;
         state.mode = value;
       }
     }
@@ -243,8 +242,12 @@ function Pin(options) {
 Pin.prototype.write = function(value) {
   var state = priv.get(this);
 
-  if (state.isPwm) {
-    state.pin._port.sock.write(new Buffer([Port.CMD.ANALOG_WRITE, value >> 8, value & 0xff]));
+  if (state.isPwm || state.isServo) {
+    if (state.index === 15) {
+      state.pin._port.sock.write(new Buffer([Port.CMD.ANALOG_WRITE, value >> 8, value & 0xff]));
+    } else {
+      state.pin.pwmDutyCycle(value);
+    }
   } else {
     state.pin.write(value);
   }
@@ -299,6 +302,10 @@ function Tessel(options) {
   options = options || {};
 
   var state = {
+    pwm: {
+      // MHz
+      frequency: null,
+    },
     i2c: {
       // Defaults to Port A I2C bus
       bus: ToPortI2CBus(options.i2c !== undefined ? options.i2c.bus : 4),
@@ -348,7 +355,7 @@ Tessel.prototype = Object.create(Emitter.prototype, {
 });
 
 Tessel.prototype.setSamplingInterval = function(ms) {
-  samplingInterval = Math.min(Math.max(ms, 10), 65535);
+  samplingInterval = Math.min(Math.max(ms, 5), 65535);
   global.clearInterval(read.interval);
   read();
 };
@@ -412,16 +419,56 @@ Tessel.prototype.analogRead = function(pin, handler) {
   return this;
 };
 
+var PWM_FREQUENCY = 490;
+var PWM_MIN = 0;
+var PWM_MAX = 1;
+
+var SERVO_FREQUENCY = 50;
+var SERVO_MIN = 0.03;
+var SERVO_MAX = 0.12;
+
+var pwms = [5, 6, 13, 14, 15];
 
-// This is not really correct, but the resulting behavior is observably similar.
 Tessel.prototype.pwmWrite = function(pin, value) {
-  this.pins[ToPinIndex(pin)].write(scale(constrain(value, 0, 255), 0, 255, 0, 1023));
+  var state = priv.get(this);
+  var index = ToPinIndex(pin);
+  var constrained = constrain(value, 0, 255);
+  var output = 0;
+
+  if (pwms.includes(index)) {
+    // For B7/15, use the DAC
+    if (index === 15) {
+      output = scale(constrained, 0, 255, 0, 1023) | 0;
+    } else {
+      if (state.pwm.frequency !== PWM_FREQUENCY) {
+        state.pwm.frequency = PWM_FREQUENCY;
+        tessel.pwmFrequency(PWM_FREQUENCY);
+      }
+      output = scale(constrained, 0, 255, 0, 1);
+    }
 
+    this.pins[index].write(output);
+  }
   return this;
 };
 
 Tessel.prototype.analogWrite = Tessel.prototype.pwmWrite;
 
+Tessel.prototype.servoWrite = function(pin, value) {
+  var state = priv.get(this);
+  var index = ToPinIndex(pin);
+  var constrained = constrain(value, 0, 180);
+
+  if (pwms.slice(0, -1).includes(index)) {
+    if (state.pwm.frequency !== SERVO_FREQUENCY) {
+      state.pwm.frequency = SERVO_FREQUENCY;
+      tessel.pwmFrequency(SERVO_FREQUENCY);
+    }
+    this.pins[index].write(scale(constrained, 0, 180, 0.03, 0.12));
+  }
+  return this;
+};
+
 // Note: Tessel-IO will default to Port A if no bus is specified.
 Tessel.prototype.i2cConfig = function(options) {
   var state = priv.get(this);
@@ -591,7 +638,7 @@ function constrain(value, low, high) {
 
 function scale(value, fromLow, fromHigh, toLow, toHigh) {
   return ((value - fromLow) * (toHigh - toLow) /
-      (fromHigh - fromLow) + toLow) | 0;
+      (fromHigh - fromLow) + toLow);
 }
 
 if (process.env.IS_TEST_ENV) {

test/tessel-mock.js

@@ -21,6 +21,8 @@ function Tessel() {
   this.version = 2;
 }
 
+Tessel.prototype.pwmFrequency = function(frequency, cb) {};
+
 Tessel.Port = function(name, socketPath, board) {
   var port = this;
 
@@ -316,6 +318,8 @@ Tessel.Pin.prototype.readPulse = function(type, timeout, callback) {
 var ANALOG_RESOLUTION = 4096;
 Tessel.Pin.prototype.resolution = ANALOG_RESOLUTION;
 
+Tessel.Pin.prototype.pwmDutyCycle = function(duty, callback) {};
+
 Tessel.Pin.prototype.analogRead = function(cb) {
   if (!this.analogSupported) {
     console.warn("pin.analogRead is not supoprted on this pin. Analog read is supported on port A pins 4 and 7 and on all pins on port B");
@@ -548,6 +552,8 @@ var CMD = {
   TXRX: 18,
   START: 19,
   STOP: 20,
+  PWM_DUTY_CYCLE: 27,
+  PWM_PERIOD: 28,
 };
 
 var REPLY = {