I've got some problems with the emulator I'm developing.
I started to develop the PPU and made the function to draw the background. The algorithm is simple, I'm not worried about color yet, so i'm just using the nametable and the pattern table, and 4 color that i manually set, just for test purpose.
Well, my problem is when it shows the screen, the screen is completely wrong.
It should show the main screen of Super Mario Bros, but it show this:
These others are from Tennis and 10-Yard Fight:
I don't think the problem is with my algorithm, but here it is anyway (I'm using python by the way):
This is the main loop:
I'm not sure where is the problem.
I think the nametable is wrong, but I don't know what I'm doing wrong.
Thank you ... and sorry for the bad english (i'm brazilian).
I started to develop the PPU and made the function to draw the background. The algorithm is simple, I'm not worried about color yet, so i'm just using the nametable and the pattern table, and 4 color that i manually set, just for test purpose.
Well, my problem is when it shows the screen, the screen is completely wrong.
It should show the main screen of Super Mario Bros, but it show this:
These others are from Tennis and 10-Yard Fight:
I don't think the problem is with my algorithm, but here it is anyway (I'm using python by the way):
Code:
def drawBackground(self):
tileY = self.cpu.scanline / 8
Y = self.cpu.scanline % 8
for i in range(32):
ptrAddress = self.VRAM[self.nameTableAddress + i + (tileY*0x20)]
#ptrAddress = self.VRAM[0x2400 + i + (tileY*0x20)]
pattern1 = self.VRAM[self.backgroundPatternTable + (ptrAddress*16) + Y]
pattern2 = self.VRAM[self.backgroundPatternTable + (ptrAddress*16) + Y + 8]
for j in range(8):
bit1 = ((1 << j) & pattern1) >> j
bit2 = ((1 << j) & pattern2) >> j
colorIndex = (bit2 << 1) | bit1
if colorIndex == 0:
color = (255, 0, 0)
elif colorIndex == 1:
color = (0, 255, 0)
elif colorIndex == 2:
color = (0, 0, 255)
else:
color = (0, 0, 0)
pygame.Surface.set_at(self.screen, (((i*8) + ((j * (-1)) + 7)), self.cpu.scanline), color)
tileY = self.cpu.scanline / 8
Y = self.cpu.scanline % 8
for i in range(32):
ptrAddress = self.VRAM[self.nameTableAddress + i + (tileY*0x20)]
#ptrAddress = self.VRAM[0x2400 + i + (tileY*0x20)]
pattern1 = self.VRAM[self.backgroundPatternTable + (ptrAddress*16) + Y]
pattern2 = self.VRAM[self.backgroundPatternTable + (ptrAddress*16) + Y + 8]
for j in range(8):
bit1 = ((1 << j) & pattern1) >> j
bit2 = ((1 << j) & pattern2) >> j
colorIndex = (bit2 << 1) | bit1
if colorIndex == 0:
color = (255, 0, 0)
elif colorIndex == 1:
color = (0, 255, 0)
elif colorIndex == 2:
color = (0, 0, 255)
else:
color = (0, 0, 0)
pygame.Surface.set_at(self.screen, (((i*8) + ((j * (-1)) + 7)), self.cpu.scanline), color)
This is the main loop:
Code:
def run(self):
cyclesClock = 0
while True:
cycles = self.instructions[self.memory[self.registers['PC']]](self)
cyclesClock += cycles
if cyclesClock > 113:
cyclesClock = 0
if self.scanline >= 0 and self.scanline < 240:
self.ppu.doScanline()
elif self.scanline == 241:
self.ppu.enterVBlank()
#print "enter VBlank"
elif self.scanline == 261:
self.scanline = -1
self.scanline += 1
cyclesClock = 0
while True:
cycles = self.instructions[self.memory[self.registers['PC']]](self)
cyclesClock += cycles
if cyclesClock > 113:
cyclesClock = 0
if self.scanline >= 0 and self.scanline < 240:
self.ppu.doScanline()
elif self.scanline == 241:
self.ppu.enterVBlank()
#print "enter VBlank"
elif self.scanline == 261:
self.scanline = -1
self.scanline += 1
I'm not sure where is the problem.
I think the nametable is wrong, but I don't know what I'm doing wrong.
Thank you ... and sorry for the bad english (i'm brazilian).
