Atari ST series Technical Reference Manual page 193

Find Valid Drive Numbers
Drvmap()
D r v m a p ( ) m a y b e u s e d t o d i s c o v e r w h a t d i s k d r i v e s a r e c u r r e n t l y a t ­
t a c h e d .
C macro format
l o n g d r i v e s ;
d r i v e s = D r v m a p ( );
Machine language format
m o v e . w # 1 0 , - (s p )
t r a p # 1 3
a d d q .l # 2 , s p
Inputs
N o n e
Results
DO d r i v e s l o n g
Drvmap
A b it f la g t h a t i n d i c a t e s w h i c h d r i v e s a r e c o n n e c t e d .
E a c h b i t c o r r e s p o n d s to a d i f f e r e n t d r i v e s , w i t h b i t 0
s t a n d i n g f o r d r i v e A : , b i t 1 f o r d r i v e B :, a n d s o o n . A
1 in a b i t p o s i t i o n m e a n s t h e d r i v e is c o n n e c t e d ,
w h i l e a 0 m e a n s it i s n 't . If d r i v e A : is p r e s e n t , d r iv e
B : is a l w a y s p r e s e n t a l s o , b e c a u s e if t h e r e is n o p h y s ­
ic a l B d r i v e , t h e s y s t e m u s e s d r i v e A : a s a lo g ic a l
d r i v e B :.
Opcode = 10
185