ALMA Integrated Computing Team Coordination & Planning Meeting #3 Socorro, June 2014 Observation with ACA correlator for Cycle3 Manabu Watanabe NAOJ

ICT-CPM June 2014 n ACA correlator has a bug to get bad channels. n In MBR telecon on 16 May 2014, we have made decisions for Cycle 2 as:  Full array mode will be used with ACA correlator.  FPS will be used even when bad channels will be output.  The fact is that 5 B grade (1.4%) among 353 A+B projects for Cycle 2 require ACA where bad data will be emerged at up to tens channels near the band edges. n The bug will not be likely fixed yet for Cycle 3. n How could we live with the ACA correlator for Cycle 3 given the persisting bug? Background & purpose

ICT-CPM June 2014 n ACA correlator frequently outputs bad data at multiple channels during observations. n We believe the problem is caused by a few bugs in logic circuit of FPGAs in the ACA correlator. n The location of failure in the logic circuit of FPGA is not determined yet. n Experience has shown that the occurrence or absence of bad channels depends only on the spectral spec, but not on the input data. Problem overview

ICT-CPM June 2014 n It will take a long time to understand thoroughly & resolve the underlying cause. n Plan for 2014 fiscal year  May- and Jun-2014: a preparation phase. the posterior analysis of the problems.  Jul-, Aug- and Sep-2014: the logic design analysis, mapping between failures and circuits. small-scale simulations.  Oct-, Nov- and Dec-2014: large-scale simulations to reproduce the problem and to give a theoretical grounding to the occurrence condition.  Jan-, Feb- and Mar-2015: the proposal of the fix and/or countermeasures Investigation and fix

ICT-CPM June 2014 n No theory for the error prediction  Brute force attack n 56,344 spectral specs have been confirmed at present  Up to 4-spw for the full-array  1-spw for 2-subarrays n Bad channels only with FPS (No errors w/o FPS, so far)  Full-array: 3% cases affected (360: errors/11,478: no errors) 7.6kHz- or 15.3kHz-channel spacing for 1-polarization. 15.3kHz-channel spacing for 2- or 4-polarizations. 1GHz BW, 1ms dump duration, 1-polarization & 64ch for the last-spw.  2-subarrays (808: errors/888: no errors) Error for about a half of confirmed spectral specs. Study of occurrence condition

ICT-CPM June 2014 n Full-array mode with ACA correlator.  But at the same time, we will continue the brute force attack for the remaining spectral specs.  Up to 4-spw for 2 subarrays which share the same spectral specs between them by March n Add the usage information of FPS to ASDM  This information is needed intrinsically for ARCHIVE users. n Align spw in ascending order of bandwidth by ALMA-OT  This will dramatically reduce the number of spectral specs to be tested in the light of errors with the 64ch last spw. n 4 options for the FPS (next slide)  We recommend the “FPS online with CDP computers” option Workaround proposal for Cycle 3

ICT-CPM June 2014 n No FPS  Difference will be 2%-3% typically, 10% at most compared to the frequency profile of the BL correlator. n FPS online with ACA correlator  Live with the bad channels problem. n FPS online with CDP computers  Difference will be 1%-2% typically, 5% at most compared to that for FPS with ACA correlator. n FPS offline with CASA  Equal to FPS with CDP for the spectral averaging factor = 1  No simulation yet for the spectral averaging factors > 2 4 options for FPS for Cycle3 (1)

ICT-CPM June options for FPS for Cycle3 (2) explain with an example provided by T.Kamazaki