APPENDIX K
vblsem
1 1 0 6 - 1 1 0 7 < $ 4 5 2 -$ 4 5 3 )
A se m a p h ore fo r ve rtica l b lan k in te rru p t p ro ce ssin g . A va lu e of 0 h ere d is
ab les vb la nk p ro ce s sin g , w h ile a va lu e of 1 en ab les p ro cessin g .
nvbls
1 1 0 8 -1 1 0 9 ($ 4 5 4 - $ 4 5 5 )
T h e n u m b er of d efe rred ve rtica l blan k in terru p t h an dler v ecto rs in th e ta
ble p oin te d to b y
__
vb lqu eu e (se e below ). T h es e are slots w h ere ap p lica
tio ns ca n tack o n th eir o w n vertical blan k in te rru p t h an d le rs . T h e d efau lt
n u m b er o f slo ts th a t T O S allo ca tes is 8.
__
vblqueue
1 1 1 0 - 1 1 1 3 ( $ 4 5 6 - $ 4 5 9 )
T h e v e rtical b lank in terru p t (V BI) q u eu e. VBI p ro ce ssin g starts a t th e po in t
w h en th e v id eo d isp lay 's e lec tro n b eam h as fin ish ed u p d atin g th e last lin e
of th e scre en d isp lay , a n d fin ish es be fo re it sta rts u p d atin g th e first line of
th e n ex t scre en fram e. D e p en din g o n w h a t k ind of scre en is u se d , th is in
te rru p t w ill o cc u r e v e ry 1/5 0 se c o n d (E u ro p e an colo r m o n ito r), e v ery 1/60
se co n d (U .S . c o lo r m on ito r), o r e ve ry 1/70 se co n d (m on o ch ro m e m on ito r).
A n u m b er of ro u tin e sy ste m fu n ctio n s a r e carrie d o u t b y th e d efa ult ve rti
cal blan k in te rru p t ha n d ler. T h ese in clu d e blink in g th e cu rs o r, ch eck in g for
a sh ift b etw e en m o n o ch ro m e a n d co lo r m o n ito rs , an d o th er vid eo -rela ted
task s w h ich a re b es t p erfo rm ed w h en th e scre en is n o t be in g u p d ated .
B e cau se th e ve rtical b lan k in g in terv al is th e p erfect tim e for m a k in g
g ra p h ics ch an g e s, it is often de sirab le for a p p licatio n s to in sert th eir h an
d lers in to th e v ertica l blank in te rru p t h an d le r ch ain . T o this e nd , T O S su p
p o rts th e in stallatio n o f deferred VBI h an d le rs. T O S in itially allo cates a tab le
th at ca n ho ld th e a d d res ses of u p to e ig ht d eferred VBI slots (th e n u m b er
is s to re d in nv b ls, a b o v e). T h e a d d re ss of this table is sto re d in th is lo ca
tio n, v b lq u e u e . J u st b e fo re th e sy stem in te rru p t h an d ler ro u tin e retu rn s, it
ch eck s th e c on te n ts o f e a ch o f th e se e ig h t a d d re sse s in tu rn . If it fin ds a
n o n ze ro v alu e in th e first o n e , it a ssu m e s it to b e th e ad d re s s of a d eferre d
V BI ha n d ler, a n d p erfo rm s a JS R to th at a d d res s. W h en th e first su b ro u
tin e is co m p le te d , th e sy ste m in terru p t h an d le r c h eck s th e n e xt slot, an d
so o n , un til it e n co u n te rs a va lu e o f z e r o in th e vb lq u eu e tab le.
In o rd e r to in stall y o u r o w n in terru p t ha n d ler, y ou m u s t e xa m in e th e
en trie s in th e tab le p o in te d to b y vb lq ue u e. Y o u m ay in stall y o u r V BI h an
d ler a t th e first tab le e n try th at co n tain s a 0 . Y o u r h an dler m ay u se an y
re giste rs e xc ep t th e u s e r stack p o in te r. It sh o u ld retu rn w ith an R TS in
stru ctio n , n o t an R T E. Be s u re to cle ar th e a d d re ss o f y o u r h an d le r fro m
th e vb lq u eu e tab le before y o u r ap plication clo ses.
T h e ST s ys te m is n o t lim ited to eig h t d eferred V BI h an d le rs. If th e ta
ble p o in te d to b y vb lq u e u e is full, y o u m a y w ish to alloca te a larg er table,
co p y th e co n te n ts o f th e vb lq u eu e tab le to it, an d th en u p d ate nv b ls a n d
vb lq u eu e to reflect th e n ew tab le size a n d loca tio n . B e su re to re sto re th e
old tab le b efo re y o u r a pp licatio n ex its.
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