Model PPS grid and BSN grid for LOFAR2.0 timing.

applications/lofar2/doc/prestudy/station2_sdp_timing.py

+###############################################################################
+#
+# Copyright 2019
+# ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>
+# P.O.Box 2, 7990 AA Dwingeloo, The Netherlands
+# 
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+# 
+#     http://www.apache.org/licenses/LICENSE-2.0
+# 
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+###############################################################################
+
+# Author: Eric Kooistra
+
+"""Show PPS and SDP timing grid information for LOFAR2.0 Station
+
+Usage:
+> python station2_sdp_timing.py -h
+
+"""
+
+import argparse
+import math
+
+figNr = 1
+
+# Parse arguments to derive user parameters
+_parser = argparse.ArgumentParser('station2_sdp_timing')
+_parser.add_argument('-n', default=10, type=int, help='Number of seconds')
+_parser.add_argument('-f', default=200, type=int, help='Sample frequency in [MHz]')
+_parser.add_argument('-q', default=32, type=int, help='Oversampling rate 32/q')
+args = _parser.parse_args()
+
+Nsec = args.n
+fadc = args.f * 1000000              # ADC sample frequency in [Hz]
+Tadc = 1000. / args.f                # ADC sample period in [ns]
+p    = 32
+q    = args.q                        # Subband oversampling rate for Ros = p / q, where p = 32
+
+Nsub     = 512                       # Number of subbands
+Ncomplex = 2
+Nfft     = Nsub * Ncomplex           # Subband filterbank FFT size
+Nblk     = Nfft * q / p              # Subband period in [Tadc]
+Tsub     = Nblk * Tadc               # Subband period in [ns]
+
+# Check that Tsub can be expressed as an integer number of ns 
+result = 'PASSED'
+if int(Tsub) != Tsub:
+    print ''
+    result = 'WARNING'
+    print 'Warning: Tsub = %f ns, choose f such that Tsub is an integer number of ns' % Tsub
+
+print ''
+print '    SSN |      first                    ToD |                 |  nof BSN'
+print ' of PPS | BSN in PPS               at first |          offset |   in PPS'
+print '   grid |   interval *  Tsub =          BSN |          to PPS | interval'
+print '    [s] |               [ns]           [ns] |   [ns]   [Tadc] |         '
+print '--------+-----------------------------------+-----------------+---------'
+# BSN = Block Sequence Number of first block in this PPS interval
+BSN = 0
+nofBSN_hi = 0
+nofBSN_lo = 0
+prevToffset = 0
+for SSN in range(Nsec):
+    # SSN = Second Sequence Number of this PPS interval
+    
+    # Determine BSN of first block in next PPS interval
+    nextSSN = SSN + 1
+    nextBSN = math.ceil((1.0 * nextSSN * fadc) / Nblk)
+    
+    # Determine timing for this PPS interval
+    # . Time of Day at BSN in [ns]
+    ToD_ns = BSN * Tsub
+    
+    # . Offset of ToD at BSN relative to PPS in [Tadc]
+    Toffset = BSN * Nblk - SSN * fadc
+    # Note: ToD_ns - SSN * 1000000000 yields Toffset in [ns], but first
+    # derive Toffset in [Tadc] units. to avoid the division (which could
+    # lead to integer truncation but not for f = 160 or f = 200) that is
+    # used to calculate ToD_ns.
+    
+    # . Number of blocks in this PPS interval
+    nofBSN = nextBSN - BSN
+    # . Maintain count of number of BSN intervals with 1 extra BSN
+    if SSN == 0:
+        nofBSN_H = nofBSN
+        nofBSN_L = nofBSN
+        nofHiBSN = 1
+        nofLoBSN = 0
+    else:
+        if nofBSN_H == nofBSN:
+            nofHiBSN += 1
+        else:
+            nofBSN_L = nofBSN     # nofBSN_H = nofBSN_L + 1 by design
+            nofLoBSN += 1
+    # Print timing information
+    if Toffset == 0 and prevToffset != 0:
+        # insert divider row each time BSN grid coincides with PPS grid again
+        print '        |                                   |                 |         '
+    print '%7d | %10d * %5d = %12d | %6d %8d | %8d' % (SSN, BSN, Tsub, ToD_ns, Toffset*Tadc, Toffset, nofBSN)
+
+
+    # Prepare for next PPS interval
+    BSN = nextBSN
+    prevToffset = Toffset
+    
+print ''
+if nofBSN_H != nofBSN_L:
+    print 'nofBSN = %d occured %d time' % (nofBSN_H, nofHiBSN)
+    print 'nofBSN = %d occured %d time' % (nofBSN_L, nofLoBSN)
+    timeBSN    = (nofBSN_H * nofHiBSN + nofBSN_L * nofLoBSN)
+    timeBSN_ns = timeBSN * Tsub
+    timeSSN_ns = Nsec * 1000000000
+      
+    print 'time SSN = %d [ns]' % timeSSN_ns
+    print 'time BSN = %d [ns] = %d * %d + %d * %d = %d [Tsub]' % (timeBSN_ns, nofBSN_H, nofHiBSN, nofBSN_L, nofLoBSN, timeBSN)
+    if timeBSN_ns != timeSSN_ns:
+        result = 'WARNING'
+        print 'Warning: not an integer number of BSN in n PPS intervals, choose n multiple of q'
+print ''
+print result
+print ''