From 28fd6aeacf2d7a57246f6a9fce6c36dc7995c109 Mon Sep 17 00:00:00 2001 From: Eric Kooistra <kooistra@astron.nl> Date: Fri, 7 Aug 2020 17:56:46 +0200 Subject: [PATCH] Discussed S_sub_bf = 512 instead of 488. --- .../lofar2/doc/prestudy/station2_sdp_ring.txt | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/applications/lofar2/doc/prestudy/station2_sdp_ring.txt b/applications/lofar2/doc/prestudy/station2_sdp_ring.txt index aa45cc1933..36ad9f70b8 100755 --- a/applications/lofar2/doc/prestudy/station2_sdp_ring.txt +++ b/applications/lofar2/doc/prestudy/station2_sdp_ring.txt @@ -47,6 +47,19 @@ the data rate for one full band station beam is N_pol * S_sub_bf * f_sub * N_com W_beamlet_sum = 2 * 488 * 195312.5 * 2 * 18 = 6.8625 Gbps. Using L_lane = 7.8125 Gbps this leaves about 1 - 6.8625 / 7.8125 = 12% margin for packet overhead, which is sufficient. +On the lane: +Using s_sub_bf = 488 yields 6.8625 Gbps, so 1 - 6.8625 / 7.8125 = 12.1% margin +Using s_sub_bf = 496 yields 6.975 Gbps, so 1 - 6.975 / 7.8125 = 10.7% margin +Using s_sub_bf = 512 yields 7.2 Gbps, so 1 - 7.2 / 7.8125 = 7.8% margin + +In the dp_clk domain: +Using 488 yields 512 / 488 = 4.9 % margin +Using 496 yields 512 / 496 = 3.2 % margin +Using 512 has no margin, so requires higher dp_clk rate to be able to insert headers. + +Design decsision: + Use dp_clk = 200 MHz, so do not overclock to support S_sub_bf = 512. It may be feasible to + support S_sub_bf = 496, but assume 488 because that is required. Design descision: Use W_beamlet_sum = 18 bit for both critically sampled beamlet and oversampled beamlets. -- GitLab