( SPI interface to MMC disk )
 : BITS-ON  ( mask -)  IOSET !  ;
 : BITS-OFF ( mask -)  IOCLR !  ;
 : PIN13 ( - mask)     $00002000  ;
 : DISABLE-MMC ( -)    PIN13 BITS-ON   ;
 : ENABLE-MMC  ( -)    PIN13 BITS-OFF  ;
 : SPI!@ ( c - c)  ( send a byte then collect the returned byte)
   SPDR !  BEGIN SPSR @ $80 AND UNTIL SPDR @  ;
 : SPI!  ( c -)  ( sned a byte but throw away returned byte)
   SPI!@ DROP  ;
 : SPI@ ( - c) ( send a dumm byte and collect returned byte)
   $FF SPI!@ ;
 : DUMMY-SPI-BYTES ( # -) FOR $FF SPI! NEXT  ;

 : GET-MMC-RESPONSE ( - f)
   ( Try up to 256 times to get a response.  A zero response          )
   (  means no error.  A valid response is a byte whose MSBit is zero.)
   (  Return -1 in case of a time-out. )
   256 ( remaining tries)   ( fall through to next word)
 : (GET-MMC-RESPONSE ( remaining# - f)    (  PAUSE  )
   SPI@ DUP $80 AND NOT IF NIP ( cardResponse)  ; THEN DROP
   ( remaining#)  1- DUP 0= IF DROP -1 ; THEN
   (GET-MMC-RESPONSE  ;

FIXME:…