First off, thanks to everyone who helped correct/optimize my code - I
look to post something more functional soon.
Could someone please explain bit.w's functionality? I have a rather
lame 6502 instruction set ref (HTML page) which is
for 7800 and does not show opcodes, among other things...
Maybe someone out there has a link to a better opcode ref - If so I (and
the list, no doubt) would sure appreciate hearing about it.
Also, I assume the reason the .byte $2c opcode is being used is because
the opcode is undocumented (or maybe just un-supported by DASM?) If so,
anyone out there know of any hacks to DASM to enable this and other
un-supported 6507 mnemonics?
BTW, Thomas Jentzsch provided the following code in response to my
question RE: better boundary detection - it is from this that
I derive my questions (full source code further down in this mail):
>> bcc
.inXBounds
>> lda #RIGHT_BOUND
>> .byte $2c
; opcode for bit.w, this hides the
next instruction
<--
I don't understand? (Wade)
>>.outOfLeftBound:
>> lda #LEFT_BOUND
>> sta Player1X
>>.inXBounds:
Thanks,
Wade
At 09:23 AM Tuesday 7/31/2001, you wrote:
Wade Brown wrote:
> I am working on a "shell" that I can use to flesh out some
ideas I have -
> the idea being to have basic semi-reusable functions such as: b/w
color
> selection, screen saver timer, and score digits.
That's a good idea, if you want to start programming the 2600. Later on,
you will find, that often you need more specialized or optimized code.
> BTW, I was trying to get a fairly optimal way to read diagonals from
the
> joystick - anyone out there see how I can improve this approach or
has a
> different take, I would really like to see...
The code below is a bit more compact than yours:
; check joystick:
lda SWCHA
asl
bcc .noRight
inc Player1X
bcs .withJoy
;3 always taken branch, saves 1 byte
compared to jmp
.noRight:
asl
bcc .noLeft
inc Player1X
bcs .withJoy
;3 always taken branch, saves 1 byte
compared to jmp
.noLeft:
asl
bcc .noDown
...
bcs .withJoy
;3 always taken branch, saves 1 byte
compared to jmp
.noDown:
asl
bcc .noJoy
...
.withJoy:
ldy
#0
; joystick moved
sty SaverTimer
.noJoy:
> I would especially appreciate any help in the
> area of boundary detection (i.e detecting when the player/enemy is
at the
> edge of the screen).
Here is a slightly better solution:
; check x-bounds:
; I LOVE to use constants, because that makes the code more readable (for
me:) and I can much easier change the parameters
LEFT_BOUND = 20
RIGHT_BOUND = 140
lda Player1X
cmp #LEFT_BOUND
bcc .outOfLeftBound
cmp #RIGHT_BOUND+1
bcc .inXBounds
lda #RIGHT_BOUND
.byte $2c
; opcode for bit.w, this hides the
next instruction
.outOfLeftBound:
lda #LEFT_BOUND
sta Player1X
.inXBounds:
You could also combine the joystick and boundary routines. This might
give you more optimal solutions. But that's mixing two different basic
functions and doesn't fit into your concept.
Have fun!
Thomas
BTW: I don't think a screensaver mode is necessary any more. And it
"wastes" a lot of valuable space.
_______________________________________________________
Thomas Jentzsch | ***
Every bit is sacred ! ***
tjentzsch at web dot de |
______________________________________________________________________________
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