APPENDIX K
sav__contxt
1198-1201 ($4AE-$4B1)
P o in te r to a te m p o ra ry b u ffe r w h ere th e p ro ce sso r c o n tex t is sa v ed .
__
bufl
1202-1209 ($4B2-$4B9)
T w o p o in te rs to G E M D O S bu ffer list h ea d ers. E ach p o in ts to a B u ffer C o n
trol B lock (B C B ), w h ic h is laid o u t a s follo w s:
struct BCB
{
BCB
*b
_
link;
f* ptr to next BCB *1
int b
_
bufdrv;
/* drive number, or -1 *1
int
b
_
buftyp;
/* buffer type */
int
b
_
bufrec;
/* record number in this buffer *1
int b__dirty /* dirty (buffer changed) flag *1
DMD
*b__dm
I* ptr to Drive Media Descriptor *1
char
*b
__
bufr
/* ptr to buffer */
T h e first bu ffer is u sed to s to re d ata s e cto rs, th e se co n d is u se d to store
FA T a n d direc to ry se c to rs.
__
hz
__
200
1210-1213 ($4BA-$4BD)
C o u n te r fo r 2 0 0 H z tim e r. D iv id ed by 4 for th e 5 0 H z sy ste m clock. T h is
v alu e is u se d as th e sta rtin g se ed th e first tim e R a n d o m () is called .
the
_
env
1214-1217 ($4BE-$4C1)
T h e de fau lt en v iro n m en t strin g, w h ich co n sists of fou r 0 by tes.
__drvbits
1218-1221 ($4C2-$4C5)
Ind icates w h ich d riv es are co n n ec te d . E ach o f th e 32 bits o f t h e
__
d rvb its
variab le co rre sp o n d s to a d iffere n t d riv e. B it 0 is as s ig n ed to d riv e A :, b it 1
to d rive B :, a n d so on u p to b it 1 5, w h ich co rres p o n d s to d riv e P : (th e
cu rre n t ve rsio n of th e ST o p eratin g sy stem on ly reco g n ize s 16 d riv es). If
th e bit w h ich co rre sp o n d s to a d riv e is s et to 1, th at d riv e is co n n e cte d ,
o th e rw ise, it is un av ailab le. T h e v alu e sto re d h ere is th e sa m e o n e re
tu rn ed b y th e B IO S fu n ctio n D r v m a p (). N o te th at if e v en o n e flop p y is
co n n e cte d , bits 0 a n d 1 a re b oth alw a ys se t to o n e. T h at's b eca u se if d riv e
A : is co n n ec te d , th e sy stem w ill u se it a s a logical d rive B: if n o p h y sical
d riv e B: is p re se n t.
400
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