looking further, I've done two things:

- modified the magma.c to verify that the driver is getting touched.

  I changed the mttyread to log the in and out counts.  Numbers change!

- connected up to a serial port on a different box, both 9600, pa=none

  0x0d (CR) appears goes out the magma as 0xfe (lotsa ones)

  0: 0x30 -> 0xfa
  1: 0x31 -> 0xfd
  2: 0x32 -> 0xfa
  3: 0x33 -> 0xff
  4: 0x34 -> 0xfb
  5: 0x35 -> 0xff
  6: 0x36 -> 0xfb
  7: 0x37 -> 0xff
  8: 0x38 -> 0xfa
  9: 0x39 -> 0xfd

Ideas?