1. fix hello.pal (in noncpu)
2. fix hello.pal (in multipdp8) (it only sees bytes with the lowest bit set)

   Command block:

             +--------------+   +----------------+
       +-----| 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:

    We only have enough pins for a single front panel, so we need an arbiter to
    control which PDP core is talking to the panel.

    Maybe the command parser should have a command for controlling that arbiter?

    Or we could repurpose some of the switches on the panel to control it? The
    DF and IF switches are sort of an obvious choice here.