dolphin/Source/Core/DSPCore/Src/DspIntBranch.cpp

// Copyright (C) 2003 Dolphin Project.

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, version 2.0.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License 2.0 for more details.

// A copy of the GPL 2.0 should have been included with the program.
// If not, see http://www.gnu.org/licenses/

// Official SVN repository and contact information can be found at
// http://code.google.com/p/dolphin-emu/

// Additional copyrights go to Duddie and Tratax (c) 2004

#include "DSPInterpreter.h"
#include "DSPCore.h"
#include "DSPMemoryMap.h"
#include "DSPStacks.h"

#include "DSPIntCCUtil.h"
#include "DSPIntUtil.h"

namespace DSPInterpreter {

// Generic call implementation
// CALLcc addressA
// 0000 0010 1011 cccc
// aaaa aaaa aaaa aaaa
// Call function if condition cc has been met. Push program counter of
// instruction following "call" to $st0. Set program counter to address
// represented by value that follows this "call" instruction.
void call(const UDSPInstruction opc)
{
	// must be outside the if.
	u16 dest = dsp_fetch_code();
	if (CheckCondition(opc & 0xf))
	{
		dsp_reg_store_stack(DSP_STACK_C, g_dsp.pc);
		g_dsp.pc = dest;
	}
}

// Generic callr implementation
// CALLRcc $R
// 0001 0111 rrr1 cccc
// Call function if condition cc has been met. Push program counter of 
// instruction following "call" to call stack $st0. Set program counter to 
// register $R.
void callr(const UDSPInstruction opc)
{
	if (CheckCondition(opc & 0xf))
	{
		u8 reg  = (opc >> 5) & 0x7;
		u16 addr = dsp_op_read_reg(reg);
		dsp_reg_store_stack(DSP_STACK_C, g_dsp.pc);
		g_dsp.pc = addr;
	}
}

// Generic if implementation
// IFcc
// 0000 0010 0111 cccc
// Execute following opcode if the condition has been met.
void ifcc(const UDSPInstruction opc)
{
	if (!CheckCondition(opc & 0xf))
	{
		// skip the next opcode - we have to lookup its size.
		dsp_skip_inst();
	}
}

// Generic jmp implementation
// Jcc addressA
// 0000 0010 1001 cccc
// aaaa aaaa aaaa aaaa
// Jump to addressA if condition cc has been met. Set program counter to
// address represented by value that follows this "jmp" instruction.
void jcc(const UDSPInstruction opc)
{
	u16 dest = dsp_fetch_code();
	if (CheckCondition(opc & 0xf))
	{
		g_dsp.pc = dest;
	}
}

// Generic jmpr implementation
// JMPcc $R
// 0001 0111 rrr0 cccc
// Jump to address; set program counter to a value from register $R.
void jmprcc(const UDSPInstruction opc)
{
	if (CheckCondition(opc & 0xf))
	{
		u8 reg  = (opc >> 5) & 0x7;
		g_dsp.pc = dsp_op_read_reg(reg);
	} 
}

// Generic ret implementation
// RETcc
// 0000 0010 1101 cccc
// Return from subroutine if condition cc has been met. Pops stored PC
// from call stack $st0 and sets $pc to this location.
void ret(const UDSPInstruction opc)
{
	if (CheckCondition(opc & 0xf))
	{
		g_dsp.pc = dsp_reg_load_stack(DSP_STACK_C);
	}
}

// RTI
// 0000 0010 1111 1111
// Return from exception. Pops stored status register $sr from data stack
// $st1 and program counter PC from call stack $st0 and sets $pc to this
// location.
void rti(const UDSPInstruction opc)
{
	g_dsp.r.sr = dsp_reg_load_stack(DSP_STACK_D);
	g_dsp.pc = dsp_reg_load_stack(DSP_STACK_C);

}

// HALT
// 0000 0000 0020 0001 
// Stops execution of DSP code. Sets bit DSP_CR_HALT in register DREG_CR.
void halt(const UDSPInstruction opc)
{
	g_dsp.cr |= 0x4;
	g_dsp.pc--;
}


// LOOP handling: Loop stack is used to control execution of repeated blocks of
// instructions. Whenever there is value on stack $st2 and current PC is equal
// value at $st2, then value at stack $st3 is decremented. If value is not zero
// then PC is modified with value from call stack $st0. Otherwise values from
// call stack $st0 and both loop stacks $st2 and $st3 are popped and execution
// continues at next opcode.
void HandleLoop()
{
	// Handle looping hardware. 
	const u16 rCallAddress = g_dsp.r.st[0];
	const u16 rLoopAddress = g_dsp.r.st[2];
	u16& rLoopCounter = g_dsp.r.st[3];

	if (rLoopAddress > 0 && rLoopCounter > 0)
	{
		// FIXME: why -1? because we just read past it.
		if (g_dsp.pc - 1 == rLoopAddress)
		{
			rLoopCounter--;
			if (rLoopCounter > 0)
			{
				g_dsp.pc = rCallAddress;
			}
			else
			{
				// end of loop
				dsp_reg_load_stack(0);
				dsp_reg_load_stack(2);
				dsp_reg_load_stack(3);
			}
		}
	}
}


// LOOP $R
// 0000 0000 010r rrrr
// Repeatedly execute following opcode until counter specified by value
// from register $R reaches zero. Each execution decrement counter. Register
// $R remains unchanged. If register $R is set to zero at the beginning of loop
// then looped instruction will not get executed.
// Actually, this instruction simply prepares the loop stacks for the above.
// The looping hardware takes care of the rest.
void loop(const UDSPInstruction opc)
{
	u16 reg = opc & 0x1f;
	u16 cnt = dsp_op_read_reg(reg);
	u16 loop_pc = g_dsp.pc;

	if (cnt)
	{
		dsp_reg_store_stack(0, g_dsp.pc);
		dsp_reg_store_stack(2, loop_pc);
		dsp_reg_store_stack(3, cnt);
	}
}

// LOOPI #I
// 0001 0000 iiii iiii
// Repeatedly execute following opcode until counter specified by
// immediate value I reaches zero. Each execution decrement counter. If
// immediate value I is set to zero at the beginning of loop then looped
// instruction will not get executed.
// Actually, this instruction simply prepares the loop stacks for the above.
// The looping hardware takes care of the rest.
void loopi(const UDSPInstruction opc)
{
	u16 cnt = opc & 0xff;
	u16 loop_pc = g_dsp.pc;

	if (cnt)
	{
		dsp_reg_store_stack(0, g_dsp.pc);
		dsp_reg_store_stack(2, loop_pc);
		dsp_reg_store_stack(3, cnt);
	}
}


// BLOOP $R, addrA
// 0000 0000 011r rrrr
// aaaa aaaa aaaa aaaa
// Repeatedly execute block of code starting at following opcode until
// counter specified by value from register $R reaches zero. Block ends at
// specified address addrA inclusive, ie. opcode at addrA is the last opcode
// included in loop. Counter is pushed on loop stack $st3, end of block address
// is pushed on loop stack $st2 and repeat address is pushed on call stack $st0.
// Up to 4 nested loops are allowed.
void bloop(const UDSPInstruction opc)
{
	u16 reg = opc & 0x1f;
	u16 cnt = dsp_op_read_reg(reg);
	u16 loop_pc = dsp_fetch_code();

	if (cnt)
	{
		dsp_reg_store_stack(0, g_dsp.pc);
		dsp_reg_store_stack(2, loop_pc);
		dsp_reg_store_stack(3, cnt);
	}
	else
	{
		g_dsp.pc = loop_pc;
		dsp_skip_inst();
	}
}

// BLOOPI #I, addrA
// 0001 0001 iiii iiii
// aaaa aaaa aaaa aaaa
// Repeatedly execute block of code starting at following opcode until
// counter specified by immediate value I reaches zero. Block ends at specified
// address addrA inclusive, ie. opcode at addrA is the last opcode included in
// loop. Counter is pushed on loop stack $st3, end of block address is pushed
// on loop stack $st2 and repeat address is pushed on call stack $st0. Up to 4
// nested loops are allowed.
void bloopi(const UDSPInstruction opc)
{
	u16 cnt = opc & 0xff;
	u16 loop_pc = dsp_fetch_code();

	if (cnt) 
	{
		dsp_reg_store_stack(0, g_dsp.pc);
		dsp_reg_store_stack(2, loop_pc);
		dsp_reg_store_stack(3, cnt);
	}
	else
	{
		g_dsp.pc = loop_pc;
		dsp_skip_inst();
	}
}

}  // namespace