Multifunction display notes (cpo, march 10, 2007)

**********************************************************************

During the RCE bootstrap, the multifunction display changes to
indicate progress.

The multifunction display is controller by the NpaBootStrap
package, file inproc.S.

Lower 2
Bytes of
Display    Meaning
--------------------
0x0001     Begin
0x0002     Completed cache invalidation, setting iccr/dccr registers
0x0003     Read page0 block0 (directory info)
0xXX04     Read status received.  Update XX = "flash operation status"
0xXX05     Check if "validation word" = 0xffffffff (sign of unformatted flash)
0xXX06     Test RLDRAM with zeroes
0xXX07     Test RLDRAM with ones
0xXX08     Try to read boot file, update XX = "flash operation status"

If an error occurs, the code sets the upper two bytes to 0xDEAD
and halts the processor.

The "flash operation status" bits are listed in rce/ffs/src/BramFunctions.hh:

enum Error {CorrectableRS, UncorrectableRS, FlashHWError, NullFileLink,
            MissingNullFileLink, ExcessData};

**********************************************************************

The slice multifunction display allocates 1 byte per slice, with
one FPGA driving it's own byte, as well as the byte of it's "neighbor".

Bottom nibble counts successful incoming frames.
Top nibble:
L - link OK
E - link error, latched by
    o nack
    o crc error
    o 8b10b error
    o sequence error (incorrect sequence number
      received)
P - waiting for link lock (pending ... state machine in progress)
F - link fail (only cause: version mismatch)
N - no link