Merge pull request #106 from bgamari/Marlin_v1

Make F_CPU dependence of stepper.cpp more explicit

Marlin/Makefile

@@ -23,7 +23,9 @@
 #  3. Set the line containing "MCU" to match your board's processor. 
 #     Older one's are atmega8 based, newer ones like Arduino Mini, Bluetooth
 #     or Diecimila have the atmega168.  If you're using a LilyPad Arduino,
-#     change F_CPU to 8000000.
+#     change F_CPU to 8000000. If you are using Gen7 electronics, you
+#     probably need to use 20000000. Either way, you must regenerate
+#     the speed lookup table with create_speed_lookuptable.py.
 #
 #  4. Type "make" and press enter to compile/verify your program.
 #
@@ -42,6 +44,8 @@ MCU = atmega1280
 #Arduino install directory
 INSTALL_DIR = ../../arduino-0022/
 
+# Be sure to regenerate speed_lookuptable.h with create_speed_lookuptable.py
+# if you are setting this to something other than 16MHz
 F_CPU = 16000000
 
 UPLOAD_RATE = 115200

Marlin/create_speed_lookuptable.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python
+
+""" Generate the stepper delay lookup table for Marlin firmware. """
+
+import argparse
+
+__author__ = "Ben Gamari <bgamari@gmail.com>"
+__copyright__ = "Copyright 2012, Ben Gamari"
+__license__ = "GPL"
+
+parser = argparse.ArgumentParser(description=__doc__)
+parser.add_argument('-f', '--cpu-freq', type=int, default=16, help='CPU clockrate in MHz (default=16)')
+parser.add_argument('-d', '--divider', type=int, default=8, help='Timer/counter pre-scale divider (default=8)')
+args = parser.parse_args()
+
+cpu_freq = args.cpu_freq * 1000000
+timer_freq = cpu_freq / args.divider
+
+print "#ifndef SPEED_LOOKUPTABLE_H"
+print "#define SPEED_LOOKUPTABLE_H"
+print
+print '#include "Marlin.h"'
+print
+
+# Based on timer calculations of 'RepRap cartesian firmware' by Zack
+# Smith and Philip Tiefenbacher.
+
+print "const uint16_t speed_lookuptable_fast[256][2] PROGMEM = {"
+a = [ timer_freq / ((i*256)+32) for i in range(256) ]
+b = [ a[i] - a[i+1] for i in range(255) ]
+b.append(b[-1])
+for i in range(32):
+    print "  ",
+    for j in range(8):
+        print "{%d, %d}," % (a[8*i+j], b[8*i+j]),
+    print 
+print "};"
+print
+
+print "const uint16_t speed_lookuptable_slow[256][2] PROGMEM = {"
+a = [ timer_freq / ((i*8)+32) for i in range(256) ]
+b = [ a[i] - a[i+1] for i in range(255) ]
+b.append(b[-1])
+for i in range(32):
+    print "  ",
+    for j in range(8):
+        print "{%d, %d}," % (a[8*i+j], b[8*i+j]),
+    print 
+print "};"
+print
+
+print "#endif"
+

Marlin/stepper.cpp

@@ -750,7 +750,13 @@ void st_init()
   // output mode = 00 (disconnected)
   TCCR1A &= ~(3<<COM1A0); 
   TCCR1A &= ~(3<<COM1B0); 
-  TCCR1B = (TCCR1B & ~(0x07<<CS10)) | (2<<CS10); // 2MHz timer
+  
+  // Set the timer pre-scaler
+  // Generally we use a divider of 8, resulting in a 2MHz timer
+  // frequency on a 16MHz MCU. If you are going to change this, be
+  // sure to regenerate speed_lookuptable.h with
+  // create_speed_lookuptable.py
+  TCCR1B = (TCCR1B & ~(0x07<<CS10)) | (2<<CS10);
 
   OCR1A = 0x4000;
   TCNT1 = 0;