( Then comes the CMD8. We send it with a 0x01aa argument and
  expect a 0x01aa argument back, along with a 0x01 R1
  response. )
    0x48 0 0x1aa  ( CMD8 )
    SDCMDR7                     ( r arg1 arg2 )
    0x1aa = NOT IF _err THEN    ( arg2 check )
    0 = NOT IF _err THEN        ( arg1 check )
    0x01 = NOT IF _err THEN     ( r check )

                                                      ( cont. )