Mario Sprites Problem

Anes · Post by **Anes** » Sat Dec 25, 2004 12:36 am

i have problems emulating super mario bros.
Mario sprites itself goes to position x = 0 after scrolling 128 pixels, and after that mario's sprites are animated but i cant move it.

Help please

Post by **Memblers** » Sat Dec 25, 2004 8:06 am

Sounds like it could be a CPU bug. Do other games work ok?

Disch · Post by **Disch** » Sat Dec 25, 2004 10:45 am

Sounds almost like a V flag problem (bad wrapping at 128 could be because the V flag is being set wrong on ADC/SBC)

Double check your ADC/SBC. For ADC... the V flag should be set when:

Positive + Positive = Negative
or
Negative + Negative = Positive

In all other instances of ADC, the V flag should be cleared.

Likewise for SBC... V flag is set when:

Positive - Negative = Negative
or
Negative - Positive = Positive

Post by **tepples** » Sat Dec 25, 2004 2:38 pm

You can make SBC always work by implementing SBC in terms of ADC: load the operand from memory as normal, invert it (^ 0xff), and then do your ADC code. Reducing complexity of your emulator's 6502 core is a good thing.

Anes · Post by **Anes** » Sat Dec 25, 2004 6:02 pm

I have tested my cpu with nestress rom and it throw me all "ok"
do i have to trust in that?

Thanks

Hyde · Post by **Hyde** » Sat Dec 25, 2004 7:00 pm

Do not trust it; I'm pretty sure there is something wrong with your ADC and SBC code (V flag).

Anes · Post by **Anes** » Sat Dec 25, 2004 7:23 pm

sure, thanks i will try

Zepper · Post by **Zepper** » Sun Dec 26, 2004 12:29 pm

tepples wrote:You can make SBC always work by implementing SBC in terms of ADC: load the operand from memory as normal, invert it (^ 0xff), and then do your ADC code. Reducing complexity of your emulator's 6502 core is a good thing.

Really? That's pretty good...
Is there any other similar case?

Anes · Post by **Anes** » Sun Dec 26, 2004 3:27 pm

Fx3 wrote: Really? That's pretty good...
Is there any other similar case?

Fx3 if you read carefully Mos 6502 manual, it says that the processor is always really adding. It inverts the bytes of the source, add carry and then add.

Zepper · Post by **Zepper** » Mon Dec 27, 2004 5:56 pm

Anes wrote:
Fx3 wrote: Really? That's pretty good...
Is there any other similar case?
Fx3 if you read carefully Mos 6502 manual, it says that the processor is always really adding. It inverts the bytes of the source, add carry and then add.

Actually, it inverts the BITS of the data (byte)...

Mario Sprites Problem

Mario Sprites Problem

Nestress

adc implementation