Atari ST series Technical Reference Manual page 264

Get Default Drive Number
Dgetdrv()
T h is f u n c t i o n a l l o w s y o u t o f in d t h e d r i v e n u m b e r o f t h e c u r r e n t d e f a u l t
d r i v e .
C macro format
in t d e f a u l t ;
d e f a u l t = D g e t d r v ( );
Machine language format
m o v e . w # $ 1 9 , - ( s p )
t r a p # 1
a d d q .l # 2 , s p
Inputs
N o n e
Results
DO d e f a u l t w o r d
See also
D s e t d r v ( )
256
Dgetdrv
T h e d r i v e n u m b e r o f t h e c u r r e n t d e f a u l t d r i v e
( d r i v e A : = 0 , d r i v e B : =
Opcode = 25 ($19)
1 , a n d s o o n ) .