2002h read and NMIs

Zepper · Post by **Zepper** » Sat Mar 08, 2008 8:46 am

- We know that reading 2002h clears the VBlank flag. Well, if NMIs are enabled, "reading 2002h near the VBL time suppress the NMI". If I change this thing to "reading 2002h suppress the NMI" still passes through the (old) test ROMs. Is this correct?

- I ask because the new test ROM fails on nmi_on_timing (5 N) and I don't know why.

hap · Post by **hap** » Sat Mar 08, 2008 8:55 am

nmi_on_timing tests NMI timing near the end of vblank by writing with bit 7 ($80) set to $2000. if 5=N, it means your edge timing is 1 PPU cycle off.

Zepper · Post by **Zepper** » Wed Mar 19, 2008 8:17 am

Still stuck. By the way, what's the meaning of those numbers anyway?

hap · Post by **hap** » Thu Mar 20, 2008 3:41 pm

Code: Select all

; Correct output:
; 01 N
; 02 N
; 03 N
; 04 N
; 05 -
; 06 -
; 07 -
; 08 -
; 09 -

The numbers don't mean anything

it's just an ordered list. Each next in the list is the result timed at 1 PPU cycle after the previous one.

Zepper · Post by **Zepper** » Sun May 04, 2008 7:16 am

- I'm still getting an error with nmi_on_timing test, 1 cycle off. Is the NMI (always) cancelled when reading 2002h?

Code: Select all

; 01 N
; 02 N
; 03 N
; 04 N
; 05 N
; 06 -
; 07 -
; 08 -
; 09 -

raidtab · Post by **raidtab** » Thu Oct 15, 2009 8:09 am

I have this exact problem, how did you fix yours?