Atari ST series - Page 190

Getbpb
Get BIOS Parameter Block
Getbpb() Opcode = 7
T h is fu n ctio n retu rn s a p o in te r to th e BIO S P ara m e te r Block , a d ata s tru c
tu re th a t co n tain s in fo rm atio n a b ou t a d isk 's s ize an d lay o ut.
C macro format
in t d riv en u m ;
lo n g block ad d r;
b lo ck ad d r = G etb p b (d riv e n u m );
M a c h i n e l a n g u a g e f o r m a t
m o v e.w # d riv e n u m , - (sp )
m o v e .w # 7 , - (sp )
trap # 1 3
ad d q .l
# 4 ,s p
I n p u ts
d riv e n um w o rd T
w ish to re ad (0 = d riv e A :, 1 = d rive B :,
a n d so o n ).
Results
DO b lo ck ad d r lo n g T h e startin g ad d re ss of th e BIO P a ra m e te r B lock.
T he P a ram e te r B lock is a d ata stru c tu re th a t co n ta in s n in e w o rd s:
Word Name Description
0 re csiz N u m b e r of b y te s p e r se cto r (m u st b e 5 1 2 u n d e r c u rren t
G E M D O S )
1 clsiz N u m b er of se cto rs p e r clu ste r (m u st be 2 u n d e r c u rre n t
G E M D O S )
2 clsizb N u m b e r o f b y tes p e r clu ste r (m u st be 10 24 u n d e r cu rre n t
G E M D O S )
3 rd len R o o t d irec to ry le n gth (in sec to rs)
4 fsiz File A lloca tio n T ab le (F A T ) size (in s ectors)
5 fatre c S ec to r n u m b er o f th e sta rt o f seco n d F A T
6 d atre c S ec to r n u m b er o f th e first d ata c lu ste r
7 n u m cl N u m b e r o f d ata c lu ste rs o n th e disk
8 bflag s B it flags. C u rre n tly o n ly bit 0 is u sed . W h en set, it
in d icate s 16-b it F A T en trie s in stead of th e u su al 12-b it
en trie s.
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