I've been trying to figure this out for a while now... The latest version
of Fall Down works fine in Stella and Z26, but several people have
reported that the title screen rolls on a real machine (I can't test it
myself).
I've been able to narrow the problem down to somewhere in the following
code... Basically, disabling everything between the lines ;-- read input
-- and .wait_overscan: makes the screen stable, but re-enabling any one
block (I've tried most of them individually) makes it roll again.
I've looked for the obvious missing # character, but couldn't find one.
Also the way I'm doing vblank hasn't changed in ages, and none of the
previous versions rolled (from what I've heard at least), so I don't think
that's the problem.
The display code right before this uses a brk to WSYNC for however many
lines. Nothing special. The code after it does a jmp (jump_addr) and
then goes into the VERTICAL_SYNC macro.
So I don't know... is there anything really obviously wrong with what
I've written here? If not, are there any common errors that only affect
real hardware?
Anyway, there's also a .bin attached if anyone wants to take a look...
-Aaron
;*****************************
;**** overscan - 30 lines ****
;*****************************
lda #2
sta VBLANK
sty PF1
sty PF2
sta WSYNC
lda #overscan_timer
sta TIM64T
lda #<display_title
sta jump_addr
lda #>display_title
sta jump_addr+1
;--- read input ---
lda #0
sta title_mode_change
ldx #5
lda SWCHB
jsr title_read_input
bcc .no_reset
lda #0
sta sound
sta sound+1
sta subsound
sta subsound+1
sta sound_timer
sta sound_timer+1
jsr advance_track
jsr title_reset_music
.no_reset:
ldx #3
.input_loop:
lda SWCHA
jsr title_read_input
dex
bpl .input_loop
ldx #4
lda SWCHB
jsr title_read_input
;--- change game mode ---
lda #nmodes ;This is the easter egg...
sta scratch ;if P0 presses up and P1 presses down,
lda SWCHA ;we increase the number of available modes
and #%00010010 ;by two.
bne .no_easter_egg
inc scratch
inc scratch
.no_easter_egg:
lax mode
clc
adc title_mode_change
bpl .mode_high_enough
lda #nmodes-1
.mode_high_enough:
cmp scratch
bcc .mode_in_bounds
lda #0
.mode_in_bounds:
sta mode
cpx mode
beq .no_mode_change
lda title_timer_h
and #%00000111
sta title_timer_h
;On every mode change, we'll reload the
;high score from the eeprom if it's present.
;This takes a whole TV frame, so first we'll
;do a quick test to see if the eeprom is
;there, and if not we can skip the whole
;thing...
jsr i2c_startwrite
bcs .no_eeprom
lda #<reset
sta jump_addr
lda #>reset
sta jump_addr+1
.no_eeprom:
jsr i2c_stopwrite
.no_mode_change:
;--- check if the game should start ---
lda INPT4
and INPT5 ;either player can start the game
and #%10000000
bne .noexit
;bit 7 is CLEAR if fire was pressed
jsr title_init_game
jmp .wait_overscan ;title_timer overlaps with the
;data that we just cleared
.noexit:
lda #title_speed
adc title_timer_l
sta title_timer_l
lda title_timer_h
adc #0
sta title_timer_h
bcc .no_attract
;go into attract mode - just the AI playing
lda #nmodes
sta mode
jsr title_init_game
.no_attract:
.wait_overscan:
lda INTIM
bne .wait_overscan
sta WSYNC
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[demime 1.01d removed an attachment of type application/x-zip which had a name of rolling_ntsc_fd.zip]
