Redraw the diagram in PLAN to make it a little prettier.

1 files changed, 46 insertions, 23 deletions

diff --git a/PLAN b/PLAN
index a4e4691..80701cd 100644
--- a/PLAN
+++ b/PLAN
@@ -1,31 +1,54 @@
 1. fix hello.pal (in noncpu)
 2. fix hello.pal (in multipdp8) (it only sees bytes with the lowest bit set)
 
-             +-----------+
-       +-----| 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 |
-             +-------+          +-----------+   +----------------+   +-------------+
-                   ^                                                             |
-                   |                                                             |
-                   +-------------------------------------------------------------+
+   Command block:
 
-    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
+             +--------------+   +----------------+
+       +-----| Echo Arbiter |<--| Result Printer |<-------------------------------+
+       |     +--------------+   +----------------+                                |
+       |       ^                                                                  |
+       v       |                                                                  |
++--------+   +----------------+                                                   |
+| UART 0 |-->| Command Parser |------------+   RAM block:                         |
++--------+   +----------------+            |                                      |
+                                           |               +----------------+     |
+                                           |               | Off-chip DRAM  |     |
+                                           |               +----------------+     |
+   PDP-8 block:                            |                 ^           |        |
+                                           |                 |           v        |
++--------+   +-------+                     |               +----------------+     |
+| UART 1 |<->| PDP-8 |                     v               | RAM Controller |     |
++--------+   +-------+                   +-------------+   +----------------+   +---------------+
+             | Cache |------------------>| Mem Arbiter |-->| Another Cache  |-->| Mem Broadcast |
+             +-------+                   +-------------+   +----------------+   +---------------+
+                   ^                       ^                                      | |
+                   |                       |                                      | |
+                   +--------------------------------------------------------------+ |
+                                           |                                        |
+           *                               |                                        |
+           * (PDP-8s are replicated)       |                                        |
+           *                               |                                        |
+                                           |                                        |
++--------+   +-------+                     |                                        |
+| UART N |<->| PDP-8 |                     |                                        |
++--------+   +-------+                     |                                        |
+             | Cache |---------------------+                                        |
+             +-------+                                                              |
+                   ^                                                                |
+                   |                                                                |
+                   +----------------------------------------------------------------+
 
+    Echo Arbiter:  Trivial priority arbiter (input echo has priority over the result printer)
+    Nen Arbiter:   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
+    Mem Broadcast: 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
+
+Note that the mem arbiter and broadcast have to be as wide as (number of
+PDP-8s)+1, so they will wind up being bottlenecks. The memory protocol allows
+arbitrary stalls, so multi-cycle arbitration is possible.
+
+Not shown is the front panel interface.
 
 
 For the front panel: