DSP2

DSP2 Gamepaks

Dungeon Master

DSP2 Status Register

The status register is a 16-bit register which holds the status bits needed by the DSP to transfer data to and from external devices. Only the upper 8 bits can be read from an external device.

The Request for Master (RQM) indicates that the DSP is requesting host CPU for data read/write.

"0" : Internal Data Register transfer.
"1" : External Data Register transfer.

DSP2 Memory Mapping

PCB	Mode	Memory Size	Bank	Data Register (DR)	Status Register (SR)
SHVC-1B5B-01	20H	8M MASKROM 256K SRAM	20H ~ 3FH	8000H ~ BFFFH	C000H ~ FFFFH

DSP2 Commands

0FH	Process Command

01H	Convert Bitmap to Bitplane Tile (Bit Perfect)
03H	Set Transparent Color (Bit Perfect)
05H	Replace Bitmap using Transparent Color (Bit Perfect)
06H	Reverse Bitmap (Bit Perfect)
07H	Add (Bit Perfect)
08H	Subtract (Bit Perfect)
09H	Multiply (Bit Perfect)
0DH	Scale Bitmap

Source Code Contributors

Reverse Engineered by Overload (Computer Science)

unsigned char xColor;

01H - Convert Bitmap to Bitplane Tile (Bit Perfect)

Input	byte(01H) byte(Bitmap[32])
Output	byte(Bitplane[32])

void DSP2_Convert(unsigned char Bitmap[32], unsigned char Bitplane[32])
{
	int Offset = 0;

	for (int i = 0; i < 16; i += 2)
	{
		unsigned char P0, P1, P2, P3;
		
		for (int j = 0; j < 4; j++)
		{
			unsigned char Data = Bitmap[Offset];
			
			P0 = (P0 << 2) + (Data & 0x01); Data >>= 1;
			P1 = (P1 << 2) + (Data & 0x01); Data >>= 1;
			P2 = (P2 << 2) + (Data & 0x01); Data >>= 1;
			P3 = (P3 << 2) + (Data & 0x01);
			
			P0 += (Data & 0x02); Data >>= 1;
			P1 += (Data & 0x02); Data >>= 1;
			P2 += (Data & 0x02); Data >>= 1;
			P3 += (Data & 0x02);
			
			Offset++;
		}
		
		Bitplane[i + 0x00] = P0;
		Bitplane[i + 0x01] = P1;
		Bitplane[i + 0x10] = P2;
		Bitplane[i + 0x11] = P3;
	}	
}

03H - Set Transparent Color (Bit Perfect)

Input	byte(03H) byte(Color)
Output	None

void DSP2_SetTransparent(unsigned char Color)
{
	xColor = Color & 0x0f;
}

05H - Replace Bitmap using Transparent Color (Bit Perfect)

Input	byte(05H) byte(n) byte(Bitmap1[n]) byte(Bitmap2[n])
Output	byte(Bitmap[n])

void DSP2_Replace(unsigned char Count, unsigned char Bitmap[255], unsigned char xBitmap[255], unsigned char nBitmap[255])
{
	for (int i = 0; i < Count; i++)
	{
		unsigned char data = xBitmap[i];

		if ((data & 0x0f) == xColor)
			data = (data & 0xf0) + (Bitmap[i] & 0x0f);

		if ((data >> 4) == xColor)
			data = (data & 0x0f) + (Bitmap[i] & 0xf0);

		nBitmap[i] = data;
	}
}

06H - Reverse Bitmap (Bit Perfect)

Input	byte(06H) byte(n) byte(Bitmap[n])
Output	byte(Bitmap[n])

void DSP2_Reverse(unsigned char Count, unsigned char Bitmap[255], unsigned char nBitmap[255])
{
	for (int i = 0; i < Count; i++)
	{
		unsigned char data = Bitmap[Count - i - 1];	
		nBitmap[i] = (data >> 4) + (data << 4);
	}	
}

07H - Add (Bit Perfect)

Input	byte(07H) double(A) double(B)
Output	double(Sum)

void DSP2_Add(int A, int B, int &Sum)
{
	Sum = A + B;
}

08H - Subtract (Bit Perfect)

Input	byte(08H) double(A) double(B)
Output	double(Difference)

void DSP2_Subtract(int A, int B, int &Difference)
{
	Difference = A - B;
}

09H - Multiply (Bit Perfect)

Input	byte(09H) integer(Multiplicand) integer(Multiplier)
Output	double(Product)

void DSP2_Multiply(short Multiplicand, short Multiplier, int &Product)
{
	int mn = Multiplicand * Multiplier << 1;
	
	// Bug is present in Dungeon Master (J) (1.0)
		
	short n = mn;
	unsigned short m = mn >> 16;
	
	n >>= 1;
	m >>= 1;
	
	Product = (m << 16) + (n & 0xffff);
}

0DH - Scale Bitmap

Input	byte(0DH) byte(n) byte(m) byte(Bitmap[(n+1) / 2])
Output	byte(Bitmap[(m+1) / 2])

0FH - Process Command

Input	byte(0FH) byte(Command) . . .
Output	None

This code must be sent to start the command processor.