jlesech · July 30, 2012 17:25 · Jul 31, 2012 · Jul 30, 2012 · Jul 30, 2012
diff --git a/pyTWI.py b/pyTWI.py
@@ -19,30 +19,28 @@
 """
 
 import argparse
-import sys 
+import sys
 
 """
-Prescaler configuration.
-"""
-class PrescalerConfiguration:
-
-    def __init__(self, prescalerValue, prescalerBits):
-        self.value = prescalerValue
-        self.bits = prescalerBits
-
-"""
-Compute rate.
+TWI bus max frequency.
 """
-def ComputeBitRate(f_cpu, f_scl, prescalerValue):
-    bitRate = (f_cpu - 16 * f_scl) / (2 * f_scl * prescalerValue)
-    return bitRate
+TWI_MAX_FREQUENCY = 400000
 
 """
 Prescaler bits in TWPS register.
 """
 TWPS0 = 0
 TWPS1 = 1
 
+"""
+Prescaler configuration.
+"""
+class PrescalerConfiguration:
+
+    def __init__(self, prescalerValue, prescalerBits):
+        self.value = prescalerValue
+        self.bits = prescalerBits
+
 """
 Available prescaler configurations.
 """
@@ -53,33 +51,38 @@ def ComputeBitRate(f_cpu, f_scl, prescalerValue):
     PrescalerConfiguration(64, ((1 << TWPS1) | (1 << TWPS0)))
 ]
 
+"""
+Compute bit rate.
+"""
+def ComputeBitRate(f_cpu, f_scl, prescalerValue):
+    bitRate = (f_cpu - 16 * f_scl) / (2 * f_scl * prescalerValue)
+    return bitRate
+
 """
 Main function.
 """
 def main():    
     # Parse arguments.
     parser = argparse.ArgumentParser()
     parser.add_argument(
-        "-f_cpu", dest = "f_cpu", default = "16000000",
+        "-f_cpu", dest = "f_cpu", type = int, default = 16000000,
         help = "CPU frequency in Hz")
     parser.add_argument(
-        "-f_scl", dest = "f_scl", default = "400000",
+        "-f_scl", dest = "f_scl", type = int, default = 400000,
         help = "SPI frequency in Hz")
     args = parser.parse_args()
 
-    print "F_CPU = " + args.f_cpu + " Hz"
-    print "F_SCL = " + args.f_scl + " Hz"
-
-    f_cpu = int(args.f_cpu)
-    f_scl = int(args.f_scl)
+    print "F_CPU = %d Hz" % (args.f_cpu)
+    print "F_SCL = %d Hz" % (args.f_scl)
 
-    # TODO: check frequencies.
+    # Check the preconditions.
+    assert(args.f_scl <= TWI_MAX_FREQUENCY)
 
     bitRate = 65535
     index = 0
 
     for index in range(len(prescalerConfigurations)):
-        bitRate = ComputeBitRate(f_cpu, f_scl, prescalerConfigurations[index].value)
+        bitRate = ComputeBitRate(args.f_cpu, args.f_scl, prescalerConfigurations[index].value)
         if bitRate <= 255:
             break
 

diff --git a/pyTWI.py b/pyTWI.py
@@ -78,7 +78,7 @@ def main():
     bitRate = 65535
     index = 0
 
-    for index in range(4):
+    for index in range(len(prescalerConfigurations)):
         bitRate = ComputeBitRate(f_cpu, f_scl, prescalerConfigurations[index].value)
         if bitRate <= 255:
             break

diff --git a/pyTWI.py b/pyTWI.py
@@ -0,0 +1,95 @@
+#!/usr/bin/env python
+# encoding: utf-8
+
+"""
+Copyright (C) 2012  Julien Le Sech - www.idreammicro.com
+ 
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+import argparse
+import sys 
+
+"""
+Prescaler configuration.
+"""
+class PrescalerConfiguration:
+
+    def __init__(self, prescalerValue, prescalerBits):
+        self.value = prescalerValue
+        self.bits = prescalerBits
+
+"""
+Compute rate.
+"""
+def ComputeBitRate(f_cpu, f_scl, prescalerValue):
+    bitRate = (f_cpu - 16 * f_scl) / (2 * f_scl * prescalerValue)
+    return bitRate
+
+"""
+Prescaler bits in TWPS register.
+"""
+TWPS0 = 0
+TWPS1 = 1
+
+"""
+Available prescaler configurations.
+"""
+prescalerConfigurations = [
+    PrescalerConfiguration(1, 0),
+    PrescalerConfiguration(4, (1 << TWPS0)),
+    PrescalerConfiguration(16, (1 << TWPS1)),
+    PrescalerConfiguration(64, ((1 << TWPS1) | (1 << TWPS0)))
+]
+
+"""
+Main function.
+"""
+def main():    
+    # Parse arguments.
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "-f_cpu", dest = "f_cpu", default = "16000000",
+        help = "CPU frequency in Hz")
+    parser.add_argument(
+        "-f_scl", dest = "f_scl", default = "400000",
+        help = "SPI frequency in Hz")
+    args = parser.parse_args()
+
+    print "F_CPU = " + args.f_cpu + " Hz"
+    print "F_SCL = " + args.f_scl + " Hz"
+
+    f_cpu = int(args.f_cpu)
+    f_scl = int(args.f_scl)
+
+    # TODO: check frequencies.
+
+    bitRate = 65535
+    index = 0
+
+    for index in range(4):
+        bitRate = ComputeBitRate(f_cpu, f_scl, prescalerConfigurations[index].value)
+        if bitRate <= 255:
+            break
+
+    # TODO: check bitrate value.
+
+    print "Bit rate (TWBR) = %d" % (bitRate)
+    print "Prescaler value = %d => prescaler bits (TWPS) = %d" % (prescalerConfigurations[index].value, prescalerConfigurations[index].bits)
+
+"""
+
+"""
+if __name__ == '__main__':
+    main()