Pass:
 - Four vertically stacked red, green, blue, and gray (in that order) 256*30
   spectrums, originating at (0, 0).
 - In each spectrum:
    - Minimum component value of 0x00 on the left, maximum of 0xFF on the right.
    - Red and blue components should be truncated to 5 bits, then scaled back up
      to 6 bits, where LSB = MSB. The difference between neighboring 8-pixel-
      wide stripes should be 2/63, except for 3/63 between the middle two.
    - Green component should be truncated to 6 bits. The difference between
      neighboring 4-pixel-wide stripes should be 1/63.
    - A black pixel in roughly the center of every 16th column.
 - White filling the 64*120 area to the right of the spectums.
 - RAM (0xD00000) viewed starting at (256, 204).

Fail:
 - Somewhat noisy 16-pixel-wide columns, cycling in color through roughly blue,
   brown, purple, and sandy, from (0, 120) to (319, 203) and (0, 204) to
   (255, 204). Side effect of DMA..?
