Rich, thanks to you and others for help, I'll probably post again when I've digested all comments and suggestions, best wishes, Neil
-----Original Message----- From: casper-boun...@lists.berkeley.edu [mailto:casper-boun...@lists.berkeley.edu] On Behalf Of Rich Lacasse Sent: 18 December 2015 20:04 To: casper@lists.berkeley.edu Subject: Re: [casper] building 300-receiver channel cross-correlator Hi Neal, Some of this may be obvious to you, but I pass it along for what it's worth. Please pardon my ASCII. I'd like this to make it through people's spam filters! As I'm sure you're aware, the general approach to correlating many antennas together tends to favor a triangular processing architecture as shown below. Grp 0 Grp 1 ... Grp M Grp N | | | | | | | | _____ _____ _____ _____ _______ Grp 0 - | C00 | -> | C01 | -> ... -> | COM | -> | C0N | --> | |_____| |_____| |_____| |_____| | | | | | __|__ __|__ __|__ | Grp 1 - | C00 | -> | C01 | -> ... -> | COM | --> | |_____| |_____| |_____| | | | | ... ... ... | DATA __|__ __|__ | ACCUM Grp M - | C00 | -> | C01 | --> | |_____| |_____| | __|__ | Grp N - | C00 | --> | |_____| |________ M = N-1 above, for notational simplicity You certainly have too much processing to do in a single ROACH. You will have to divide and conquer somehow. Grouping the samples from several antennas into groups and grouping of smaller correlators into a (at least conceptually) triangular array, as shown above would be one approach. You will probably have to add delay stages for each antenna ahead of the correlators to align the wavefront. You will also have to find a way to initially distribute the signals. 300 MHz is a little fast; you may have to back off to 150 MHz at least initially by parallelizing the data. The CASPER way of passing signals around is to use a big Ethernet switch. That would take care of all of your interconnects in the triangle above and also to the data accumulator to the right above. As an alternative architecture you may want to have a look at powerMx. See www.powermx.org Rich "Before acting on this email or opening any attachments you should read the Manchester Metropolitan University email disclaimer available on its website http://www.mmu.ac.uk/emaildisclaimer "
