From: Eddie Hung <eddie@fpgeh.com>
Date: Fri, 13 Sep 2019 16:34:40 +0000 (-0700)
Subject: Refine diagram
X-Git-Tag: working-ls180~1039^2~114
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e235dd07854ad31617a4609c59dbdeacb9323ad0;p=yosys.git

Refine diagram
---

diff --git a/techlibs/xilinx/abc_model.v b/techlibs/xilinx/abc_model.v
index 109804f09..5963258e8 100644
--- a/techlibs/xilinx/abc_model.v
+++ b/techlibs/xilinx/abc_model.v
@@ -52,10 +52,12 @@ endmodule
 //   path between AREG/BREG/CREG/etc. and P/PCOUT.
 //   Since the Aq/ADq/Bq/etc. inputs are assumed to arrive at
 //   the box at zero time, the combinatorial delay through
-//   these muxes thus represents the clock-to-q delay at
-//   P/PCOUT.
+//   these boxes thus represents the clock-to-q delay
+//   (arrival time) at P/PCOUT.
 //   Doing so should means that ABC is able to analyse the
-//   worst-case delay through to P.
+//   worst-case delay through to P, regardless of if it was
+//   through any combinatorial paths (e.g. B, below) or an
+//   internal register (A2REG).
 //   However, the true value of being as complete as this is
 //   questionable since if AREG=1 and BREG=0 (as below)
 //   then the worse-case path would very likely be through B
@@ -63,15 +65,15 @@ endmodule
 //
 //   In graphical form:
 //
-//             NEW "PI" >>---+
-//           for AREG.Q      |
-//                           |
-//            +---------+    |   __
-//    A --X X-|         |    +--|  \
-//            | DSP48E1 |P      |   |--- P
-//            | AREG=1  |-------|__/
-//    B ------|         |
-//            +---------+
+//               NEW "PI" >>---+
+//             for AREG.Q      |
+//                             |
+//              +---------+    |   __
+//    A >>--X X-|         |    +--|  \
+//              | DSP48E1 |P      |   |--->> P
+//              | AREG=1  |-------|__/
+//    B >>------|         |
+//              +---------+
 //
 (* abc_box_id=2100 *)
 module \$__ABC_DSP48E1_MULT_P_MUX (input Aq, ADq, Bq, Cq, Dq, Mq, input [47:0] P, input Pq, output [47:0] O);