APPENDIX K
etv
_
timer
1 0 2 4 - 1 0 2 7 ( $ 4 0 0 - $ 4 0 3 )
T im e r tick h an d o ff v ec to r (log ical v e cto r $ 1 0 0 ). T h e sy stem tim e r in terru p t
h an d le r (called e v ery 2 0 m illisecon d s) is u se d to m a intain th e G E M D O S
tim e-o f-d ay clo ck , d riv e th e X B IO S b ack gro u n d s ou n d rou tin e, ha n d le k ey
rep ea t, an d p e rfo rm o th e r h o u sek ee p in g ch o re s. A t th e en d of e v e r y tim er
tick , th e in te rru p t h an d ler also p erfo rm s a JSR th ro u g h this ve cto r. T o in
stall a n e w h a n d le r ro u tin e, u se S e te x e c (), a n d sa ve th e old v ec to r a d
d res s. W h en th e h a n d le r is en te re d , th e tim er tick rate (in m illise co n d s) is
o n th e stack . T h e h an d le r sh ou ld ex ec u te its o w n co d e first, a n d ex it b y
ju m p in g th ro u gh th e old v e cto r. S ince th e T O S p ortion of th e in te rru p t
h a n d le r sav es all re gis ters b efo re callin g this ro u tin e, an d re sto re s th e m af
te rw a rd s, th ere is n o n e ed fo r th e use r-in stalled rou tin e to sa ve th e m as
w ell.
etv
_
critic
1 0 2 8 - 1 0 3 1 ($ 4 0 4 - $ 4 0 7 )
C ritical e rro r h an d le r (logical v e cto r $ 10 1). T his v ecto r is called by th e B IO S
w h en certa in e rro rs (s u ch as R w a b s () d isk erro rs o r m e dia ch an g e s) o ccu r.
T h is allo w s an ap p lication to tak e ca re of its o w n e r ro r h an d lin g. W h e n
ex ecu tio n p as s es to th e h a n d le r a t th is a d d re ss, th e first w o rd o n th e stac k ,
4 (s p ), is a n erro r n u m b er, a n d o th er p a ra m ete rs m a y follow it, d ep en d in g
o n th e er ro r. T h e h a n d ler sh o u ld p res erv e re giste rs D 3 -D 7 /A 3 -A 6 , a n d
w h en it r e tu rn s , it sh ou ld place a lo n g w o rd e rro r c od e in DO:
E rro r C o d e A c tio n
0x 0 00 10 0 00 R etry
0 x0 00 00 00 0 Ig n ore th e erro r
O xF FFFFF xx A b ort w ith erro r
T h e d efa ult h an d le r m e re ly re tu rn s a - 1 L .
etv
_
term
1 0 3 2 - 1 0 3 5 ($ 4 0 8 - $ 4 0 B )
P ro ces s te rm in ate h an d le r (logical v ec to r $ 10 2). G E M D O S calls th is v ec to r
righ t b efo re it te rm in a tes a p ro ce ss . N o rm ally , this v ec to r po in ts to a n RTS
in stru ctio n , w h ich a llow s th e p ro ce ss to term in ate . If th e ap p lica tion
d o e sn 't w a n t to b e te rm in ated (b ecau se of a n accid en tal C T R L -C d u rin g
C c o n r s (), fo r e xa m p le), it ca n rega in c o n tro l h ere . Se e a lso th e criticret
v e cto r (1 16 2, $ 48 A ).
etv__xtra
1 0 3 6 - 1 0 5 5 ($ 4 0 C - $ 4 1 F )
R es erv ed for u p to five fu tu re lo gical v ec to rs ($ 1 0 3 -$ 1 0 7 ).
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