Hi, I'm trying to build an NES Emulator. I am trying to get Pacman to work and was comparing my emulator log with Nintendulator log. However, I noticed that a specific LDA Immediate in Nintendulator is taking more cycles than expected.
The first and the second line indicate that the LDA #$C0 takes 6 cycles, (4 more than expected). This looks to be a one off event because on the second last instruction and last instruction, the same instructions are run but this time LDA #$C0 expectedly take 2 cycles. Does anyone know why this happen?
Code:
C0CC A9 C0 LDA #$C0 A:1F X:08 Y:00 P:25 SP:FF PPU:291,196 CYC:81944C0CE 8D 17 40 STA $4017 = FF A:C0 X:08 Y:00 P:A5 SP:FF PPU:309,196 CYC:81950C0D1 20 4B EE JSR $EE4B A:C0 X:08 Y:00 P:A5 SP:FF PPU:321,196 CYC:81954EE4B A9 00 LDA #$00 A:C0 X:08 Y:00 P:A5 SP:FD PPU:339,196 CYC:81960EE4D 85 F0 STA $F0 = 00 A:00 X:08 Y:00 P:27 SP:FD PPU: 4,197 CYC:81962EE4F A9 06 LDA #$06 A:00 X:08 Y:00 P:27 SP:FD PPU: 13,197 CYC:81965EE51 85 F1 STA $F1 = 00 A:06 X:08 Y:00 P:25 SP:FD PPU: 19,197 CYC:81967EE53 A9 20 LDA #$20 A:06 X:08 Y:00 P:25 SP:FD PPU: 28,197 CYC:81970EE55 85 F2 STA $F2 = 00 A:20 X:08 Y:00 P:25 SP:FD PPU: 34,197 CYC:81972EE57 A9 06 LDA #$06 A:20 X:08 Y:00 P:25 SP:FD PPU: 43,197 CYC:81975EE59 85 F3 STA $F3 = 00 A:06 X:08 Y:00 P:25 SP:FD PPU: 49,197 CYC:81977EE5B AD BF F0 LDA $F0BF = C1 A:06 X:08 Y:00 P:25 SP:FD PPU: 58,197 CYC:81980EE5E 85 F4 STA $F4 = 00 A:C1 X:08 Y:00 P:A5 SP:FD PPU: 70,197 CYC:81984EE60 AD C0 F0 LDA $F0C0 = F0 A:C1 X:08 Y:00 P:A5 SP:FD PPU: 79,197 CYC:81987EE63 85 F5 STA $F5 = 00 A:F0 X:08 Y:00 P:A5 SP:FD PPU: 91,197 CYC:81991EE65 A9 40 LDA #$40 A:F0 X:08 Y:00 P:A5 SP:FD PPU:100,197 CYC:81994EE67 85 F7 STA $F7 = 00 A:40 X:08 Y:00 P:25 SP:FD PPU:106,197 CYC:81996EE69 A9 1F LDA #$1F A:40 X:08 Y:00 P:25 SP:FD PPU:115,197 CYC:81999EE6B 8D 15 40 STA $4015 = FF A:1F X:08 Y:00 P:25 SP:FD PPU:121,197 CYC:82001EE6E A9 C0 LDA #$C0 A:1F X:08 Y:00 P:25 SP:FD PPU:133,197 CYC:82005EE70 8D 17 40 STA $4017 = FF A:C0 X:08 Y:00 P:A5 SP:FD PPU:139,197 CYC:82007Statistics: Posted by minhmxc — Fri Jan 31, 2025 1:40 am — Replies 5 — Views 437