yet another pdp-11 in fgpa

Johnny Billquist <bqt at softjar.se> wrote: oops, you are right, I was mixing numbers here and forgot about a factor of four. Here the revised arguments: See http://www.village.org/pdp11/faq.pages/prfmnc.html , there is a table comparing 11/70 with various J11 systems: 11/23 11/53 11/73 11/83 11/93 ----- ----- ----- ----- ----- CPU F-11 J-11 J-11 J-11 J-11 Microcycle(ns) 300 267 267 222 222 Clock (MHz) ? 15 15 18 18 Performance 0.2 0.5 0.7 1.2 1.4 (11/70 = 1) Cache no no yes yes no Floating-Pt opt no no yes yes Coprocessor My mistake was to forget that the J11 needs 4 clock cycles per microcycle (MC), that's why 18 MHz clock leads to 222 ns MC period. In the end the J11 (222ns MC) is faster than the 11/70 (150 ns MC) because it has a better micro architecture (three stage pipeline vs. instruction prefetch only). The J11 is roughly a factor two better compared to 11/70 in terms of MC efficiency. The w11a on the other side does one microcycle per clock cycle. So one can expect that is roughly a factor 5.5 faster than a 18 MHz J11 (MC rate is 11 times higher (50/4.5), but J11 has a factor two better MC efficiency). Let's look at the Dhrystone benchmarks again: w11a 11500 lps 11/53 830 lps So the w11a is measured to be ~14 faster than a 11/53. The 11/53 has half the performance of a 11/70, so one expects that the w11a is about a factor 7 faster than a 11/70. Because w11a and 11/70 have a similar micro architecture that should match the MC rate, and indeed it does (50/6.7). So the numbers are consistent, finally. Thanks for pointing that out. Walter