SoundTrack: SECTOR / SERIOUS S.G. '97 (CMG98)
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(C) RLA / CRG
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Stack Usage
When resolving PREREYVANIYAH
It is no secret that for fast manipulation
with graphics in games and, especially, in the demonstrations
are commonly used commands stack. With their help, you can
achieve the greatest rate of work with graphics. However, the
steeper the effect, the longer it takes. There may be occasions
when effect does not have time to work out 69,888 cycles
and an interrupt occurs. Return address
discarded onto the stack and irreversibly damages
contained underneath the information. But not all
lost. We consider several cases as
You can save the data and work with
stack enabled interrupts the second
kind.
1. If there is a clearing or filling the screen with any
data, it is not so scary, because when you return from interrupt
PUSH HL continue the cycle and the return address
will be overwritten by the required data.
1.1 It is possible that the stack will be equal to 4000h
and the return address will be lost, but this
case can be controlled if you know
address those points in which this can happen and go there not
to RET'u and JP ADDRESS.
Example:
LD SP, # 4020, net the most
LD HL, # 0000 top line
PUSH HL; in the screen
PUSH HL
PUSH HL
... * 16 times
PUSH HL
PUSH HL
ADR1 LD SP, (SAVESP)
RET
The latter case is possible if the interruption wedged
between the teams PUSH HL and LD SP, (SAVESP). Handler 2 (!)
Interrupts in this case would look like:
ORG # BFBF
INT2 DI
LD (TOSP +1), SP
LD SP, INT2-1
PUSH HL
PUSH DE
PUSH BC
PUSH AF
PUSH IX
EXX
EX AF, AF
PUSH HL
PUSH DE
PUSH BC
PUSH AF
PUSH IY
LD HL, (TOSP +1)
LD DE, - # 4000
ADD HL, DE
LD A, # C9; RET
JR C, OK
LD A, # C3; JP
LD (TO_RET), A
... treatment interruption
POP IY
POP AF
POP BC
POP DE
POP HL
EXX
EX AF, AF
POP IX
POP AF
POP BC
POP DE
POP HL
EI
TOSP LD SP, 0
TO_RET DB 0
DW ADR1
2. There is another insidious case where
data through the stack will not be recorded, and
read. Most often it is consumed,
when the screen is moving most of it
Part (TRASH DEMO, ART'98, all sorts of intros to the games). In
memory of pre-created great sprite and displayed on the screen
roughly the chain of bytes:
POP HL
LD (# 4000), HL
POP HL
LD (# 4002), HL
...
POP HL
LD (# 57FE), HL
LD SP, (SAVESP)
RET
In these programs, part of the screen
time to exchange a per interrupt,
and this problem does not arise, but there were
cases, when running a single effect, and then
need to throw the top window with the wishes of
or GTX'ami. If an interrupt, then
the stack is dropped again return address
and the sprite will be "permanently damaged.
It is in such a case appealed to me
one of my friends coder. After some
time the problem was solved. Its effects
worked in the interrupt enable, and
graphics are not spoiled.
Processor:
ORG # BFBF
INT2 DI
LD (TOSP +1), SP
LD SP, INT2-1
PUSH HL
PUSH DE
PUSH BC
PUSH AF
PUSH IX
EXX
EX AF, AF
PUSH HL
PUSH DE
PUSH BC
PUSH AF
PUSH IY
LD HL, (TOSP +1)
LD E, (HL)
INC HL
LD D, (HL)
LD (_JP +1), DE
... treatment interruption
POP IY
POP AF
POP BC
POP DE
POP HL
EXX
EX AF, AF
POP IX
POP AF
POP BC
POP DE
POP HL
TOSP LD SP, 0
PUSH HL; Record
POP HL; Adjustment stack
EI
_JP JP 0
Consider the possible cases when an interrupt can occur:
a) between the teams and POP HL LD (NN), HL
Reads a byte in register HL
and before returning to the team will be recorded
PUSH HL.
b) between the commands LD (NN), HL POP HL and
data again are in the HL and recover the same manner.
It is worth noting that the return from the handler will
always be performed by direct transition.
I note that demonstrations such workarounds tricks with the
stack I have not met.
I hope that this paper will reduce the work of some of your
effects on the excess 10-20 thousand cycles are so impeded
make your impact on the Int faster.
