extruder: Create a new class and python file to track the printer extruder

Create a new python file (extruder.py) to control the extruder heater
and stepper motors.  This separates the extruder control logic from
the cartesian robot code - making it easier to customize both the
kinematic control of the robot as well as the extruder.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extruder.py

@@ -0,0 +1,62 @@
+# Code for handling printer nozzle extruders
+#
+# Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import logging
+import stepper, heater
+
+class PrinterExtruder:
+    def __init__(self, printer, config):
+        cfg = config.getsection('extruder')
+        self.heater = heater.PrinterHeater(printer, cfg)
+        self.stepper = stepper.PrinterStepper(printer, cfg)
+        self.stepper_pos = 0
+    def build_config(self):
+        self.heater.build_config()
+        self.stepper.build_config()
+    def get_max_speed(self):
+        return self.stepper.max_velocity, self.stepper.max_accel
+    def motor_off(self, move_time):
+        self.stepper.motor_enable(move_time, 0)
+    def move(self, move_time, move):
+        inv_accel = 1. / move.accel
+        new_step_pos = int(move.pos[3]*self.stepper.inv_step_dist + 0.5)
+        steps = new_step_pos - self.stepper_pos
+        if not steps:
+            return
+        self.stepper_pos = new_step_pos
+        sdir = 0
+        if steps < 0:
+            sdir = 1
+            steps = -steps
+        clock_offset, clock_freq, so = self.stepper.prep_move(sdir, move_time)
+
+        step_dist = move.move_d / steps
+        step_offset = 0.5
+
+        # Acceleration steps
+        #t = sqrt(2*pos/accel + (start_v/accel)**2) - start_v/accel
+        accel_clock_offset = move.start_v * inv_accel * clock_freq
+        accel_sqrt_offset = accel_clock_offset**2
+        accel_multiplier = 2.0 * step_dist * inv_accel * clock_freq**2
+        accel_steps = move.accel_r * steps
+        step_offset = so.step_sqrt(
+            accel_steps, step_offset, clock_offset - accel_clock_offset
+            , accel_sqrt_offset, accel_multiplier)
+        clock_offset += move.accel_t * clock_freq
+        # Cruising steps
+        #t = pos/cruise_v
+        cruise_multiplier = step_dist * clock_freq / move.cruise_v
+        cruise_steps = move.cruise_r * steps
+        step_offset = so.step_factor(
+            cruise_steps, step_offset, clock_offset, cruise_multiplier)
+        clock_offset += move.cruise_t * clock_freq
+        # Deceleration steps
+        #t = cruise_v/accel - sqrt((cruise_v/accel)**2 - 2*pos/accel)
+        decel_clock_offset = move.cruise_v * inv_accel * clock_freq
+        decel_sqrt_offset = decel_clock_offset**2
+        decel_steps = move.decel_r * steps
+        so.step_sqrt(
+            decel_steps, step_offset, clock_offset + decel_clock_offset
+            , decel_sqrt_offset, -accel_multiplier)