Added frame number operations

python/misc_utils/fn_time.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+# @file
+# @author Piotr Krysik <ptrkrysik@gmail.com>
+# @section LICENSE
+# 
+# Gr-gsm 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, or (at your option)
+# any later version.
+# 
+# Gr-gsm 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 gr-gsm; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street,
+# Boston, MA 02110-1301, USA.
+# 
+# 
+from math import floor, ceil
+from random import uniform
+
+__hyper_frame = 26*51*2048
+__symb_rate = 13.0e6/48.0
+__ts_period = 156.25/__symb_rate
+__frame_period = 8*__ts_period
+
+#The functions below are crucial part of synchronization between
+#transmitter and receiver.
+
+#fnmod_delta computes difference between two frame numbers modulo
+#__hyper_frame. The result is correct if difference between the frame
+#numbers is not bigger than __hyper_frame/2.
+def fnmod_delta(fn1, fn2):
+    h2 = __hyper_frame/2
+    delta = (fn1%__hyper_frame)-(fn2%__hyper_frame)
+  
+    if delta >= h2:
+        delta = delta - __hyper_frame
+    elif delta < -h2:
+        delta = delta + __hyper_frame
+    
+    return delta
+  
+#fn_time_delta computes difference between reference frame number and a second frame number. It also computes timestamp of the second frame number. The full list of parameters is following:
+#* fn_ref - reference frame number modulo __hyper_frame
+#* time_ref - precise timestamp of the first sample in the frame fn_ref
+#* fn_x - second frame number modulo __hyper_frame,
+#* time_hint - coarse time for fn_x that is used as a hint to avoid ambiguities caused by modulo operation applied to frame numbers. The correct are values from range <time2_precise-__hiperframe/2, time2_precise+__hiperframe/2> (where time2_precise is exact time of the first sample in frame fn_x)
+#* ts_num - number of timeslot in the frame
+
+def fn_time_delta(fn_ref, time_ref, fn_x, time_hint=None, ts_num=None):
+    if time_hint is None:
+        time_hint = time_ref
+        
+    if ts_num is None:
+        ts_num = 0
+
+    time_diff = time_hint-time_ref
+    frames_diff = int(round(time_diff/__frame_period))
+    fn_ref = (fn_ref + frames_diff)
+    fn_delta = fnmod_delta(fn_x,fn_ref)+frames_diff
+    time2_precise = fn_delta*__frame_period+time_ref+ts_num*__ts_period
+    
+    return fn_delta, time2_precise
+
+
+if __name__ == "__main__":
+    fn1 = 10000
+    time1 = 10
+    for fn2 in xrange(__hyper_frame/2+fn1-10,__hyper_frame/2*10+fn1+10,10):
+        time2 = time1 + (fn2-fn1)*__frame_period 
+        error = uniform(-6200,6200)
+        time2_err = time2+error
+        fn_delta, time2_precise = fn_time_delta(fn1, time1, fn2, time2_err)
+        if fn_delta != fn2-fn1:
+            print "dupa:", fn2, error#, 'fn_delta:'+str(fn_delta), time2, error, frames_diff_h4, (time2-time1)/(__hyper_frame*__frame_period), time_diff_h4_prev, time_diff
+        time_diff = time2 - time2_precise
+        if time_diff > 0.1:
+            print "dupa"
+