From b1d1ecaa2d244e429d1f71165cab32d272b0e0fc Mon Sep 17 00:00:00 2001
From: Julian Blake Kongslie
Date: Sun, 13 Mar 2022 16:47:08 -0700
Subject: Reformat PLAN to be a little prettier.

---
 PLAN | 41 ++++++++++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 17 deletions(-)

(limited to 'PLAN')

diff --git a/PLAN b/PLAN
index d60dec5..cc8b5d6 100644
--- a/PLAN
+++ b/PLAN
@@ -1,20 +1,27 @@
 1. fix hello.pal (in noncpu)
 2. fix hello.pal (in multipdp8) (it only sees bytes with the lowest bit set)
 
-             +---------+
-       +-----+ Arbiter <-----------------------------------------------+
-       |     +-^-------+                                               |
-       |       |                                                       |
-       |       |                                                       |
-       |       |                                                       |
-+------v-+   +-+--------------+                                      +-+--------------+
-| UART 0 +---> Command Parser +-----+                                | Result Printer |
-+--------+   +----------------+     |                                +-^--------------+
-                                    |                                  |
-             +-------+              |           +----------------+     |
-             | Cache |              |           | Another Cache  |     |
-+--------+   +-------+            +-v-------+   +----------------+   +-+-----------+
-| UART 1 +---> PDP-8 +------------> Arbiter +---> RAM Controller +---> Broadcaster |
-+--------+   +-----^-+            +---------+   +----------------+   +-+-----------+
-                   |                                                   |
-                   +---------------------------------------------------+
+             +-----------+
+       +-----| Arbiter 1 |<--------------------------------------------+
+       |     +-----------+                                             |
+       |       ^                                                       |
+       v       |                                                       |
++--------+   +----------------+                 +----------------+   +----------------+
+| UART 0 |-->| Command Parser |-----+           | Off-chip DRAM  |   | Result Printer |
++--------+   +----------------+     |           +----------------+   +----------------+
+                                    |             ^           |        ^
+                                    |             |           v        |
++--------+   +-------+              |           +----------------+     |
+| UART 1 |-->| PDP-8 |              v           | RAM Controller |     |
++--------+   +-------+          +-----------+   +----------------+   +-------------+
+             | Cache |--------->| Arbiter 2 |-->| Another Cache  |-->| Broadcaster |
+             +-------+          +-----------+   +----------------+   +-------------+
+                   ^                                                             |
+                   |                                                             |
+                   +-------------------------------------------------------------+
+
+    Arbiter 1: Trivial priority arbiter
+    Arbiter 2: Adds clog2(1 + number of PDP-8s) tag bits indicating which channel was selected
+               For inputs coming from a PDP-8 as opposed to the command parser, add the appropriate prefix to the memory address
+    Broadcaster: Removes clog2(1 + number of PDP-8s) tag bits to determine which channel to send to
+                 For outputs going to a PDP-8 as opposed to the result printer, strip excess address bits
-- 
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