Can anyone help fix my CGA on VGA emulation?

[superfury]

I'm trying to get VGA's CGA mode (BIOS Video mode 06h) working.

uint_32 patch_map1314(VGA_Type *VGA, uint_32 rowscancounter, uint_32 rowscanaddress) //Patch full VRAM address!
{
	uint_32 newrowscan = rowscanaddress; //New row scan to use!
	
	if (!VGA->registers->CRTControllerRegisters.REGISTERS.CRTCMODECONTROLREGISTER.MAP13) //a13=Bit 0 of the row scan counter!
	{
		//Row scan counter bit 1 is placed on the memory bus bit 14 during active display time.
		//Bit 1, placed on memory address bit 14 has the effect of quartering the memory.
		newrowscan = (newrowscan&(~(1<<13)))|((rowscancounter&1)<<13); //Exchange row scan counter bit 0 for bit 13!
	}

	if (!VGA->registers->CRTControllerRegisters.REGISTERS.CRTCMODECONTROLREGISTER.MAP14) //a14<=Bit 1 of the row scan counter!
	{
		newrowscan = (newrowscan&(~(1<<14)))|((rowscancounter&2)<<13); //Exchange row scan counter bit 0 for bit 13!
	}
	
	return newrowscan; //Give the linear address!
}

uint_32 addresswrap(VGA_Type *VGA, uint_32 memoryaddress) //Wraps memory arround 64k!
{
	if (!VGA->registers->CRTControllerRegisters.REGISTERS.CRTCMODECONTROLREGISTER.AW) //Put address bit 13 on bit 0?
	{
		if (VGA->registers->CRTControllerRegisters.REGISTERS.UNDERLINELOCATIONREGISTER.DW) //Doubleword mode?
		{
			return ((memoryaddress<<2)&0xFFFC)|((memoryaddress>>12)&3); //SHL 2, MA12&13 to MA0&1?
		}
		else if (!VGA->registers->CRTControllerRegisters.REGISTERS.CRTCMODECONTROLREGISTER.UseByteMode) //Word mode is used in CGA emulation?
		{
				return ((memoryaddress<<1)&0xFFFE)|((memoryaddress>>13)&1); //SHL 1, MA13 to MA1?
		}
		//Byte mode runs normally!
	}
	return memoryaddress; //Normal operating mode!
}

When the sequencer reads data from memory:

extern uint_32 rowscanaddress; //Row scan address!
extern uint_32 rowscancounter; //Row scan counter!

//Allow wrap is used to determine the hardware rendering!
uint_32 determinewrap(VGA_Type *VGA, uint_32 addr,byte is_renderer)
{
	uint_32 result = addr; //Default: take address itself!
	if (is_renderer) //Hardware side?
	{
		result -= rowscanaddress; //Substract the row scan address to get the base!
		rowscanaddress = addresswrap(VGA,rowscanaddress); //Wrap if needed!
		rowscanaddress = patch_map1314(VGA,rowscancounter,rowscanaddress); //Allow patching of MAP13&14!	
		result += rowscanaddress; //Apply new row scan address!
	}
	return result; //New offset!
}

When the renderer is calling memory reads, is_renderer==1, when the CPU executes reads/writes to video memory is_renderer==0.

The VRAM offset passed to determinewrap is calculated like this:
(((start+offset)*4)+plane)%VRAM_SIZE
VRAM_SIZE is usually 256k (4*65536)

Anyone can help me fix this (or can tell me if this is correct)?


This is supposed to be left half white, right half white.