i_bcc.c

SkyEye是一个可以运行嵌入式操作系统的硬件仿真工具

/**********************************/
/*                                */
/*  Copyright 2000, David Grant   */
/*                                */
/*  see LICENSE for more details  */
/*                                */
/**********************************/

#include "coldfire.h"

/* Branch Contitionally, Branch Always (BRA) and 
    Branch To Subroutine (BSR) instructions */

/* Format 
   
 15  14  13  12  11  10   9   8   7   6   5   4   3   2   1   0
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 1 | 1 | 0 |   Condition   |  8-Bit displacement           |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|                16-Bit displacement if 8bit is 00              |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

*/

int BRATime = 2;
int BSRTime = 3;
int BCCTime[] = { 3, 1, 2, 3 };


INSTRUCTION_3ARGS(BCC, 
	unsigned Code1,4,
	unsigned Condition,4,
	signed Displacement,8);

static void execute(void)
{

	unsigned int Displacement;
	/* The PC for the branch contains the address of the BCC
            instruction _plus two_ */
	unsigned int ReferencePC=memory_core.pc+2; 
	BCC_Instr Instr;

	Memory_RetrWordFromPC(&Instr.Code);
	Displacement=Instr.Bits.Displacement;
	if(Displacement==0) {
		Memory_RetrWordFromPC(&Displacement);
		Displacement = (short)Displacement;
	}	

	switch(Instr.Bits.Condition) {
	case 0: /* BRA */
		/* Do nothing, this is always true */
		cycle(BRATime);
		goto i_bcc_do_branch;
	case 1: /* BSR */
		/* Save the PC in the A7 stack pointer */
		Stack_Push(32, memory_core.pc);
		cycle(BSRTime);
		goto i_bcc_do_branch;
	case 2: /* BHI */
		/* Branch if not carry, or not zero */
		if(!SRBits->C && !SRBits->Z) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 3: /* BLS */
		/* Branch if low or same  */
		if(SRBits->C || SRBits->Z) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 4: /* BCC */
		/* Branch if carry cleared */
		if(!SRBits->C) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 5: /* BCS */
		/* Branch if carry set */
		if(SRBits->C) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 6: /* BNE */
		/* Branch if they are not equal, ie Dest-Source != 0 */
		if(!SRBits->Z) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 7: /* BEQ */
		/* Don't branch if they are not equal */
		if(SRBits->Z) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 8: /* BVC */
		if(!SRBits->V) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 9: /* BVS */
		if(SRBits->V) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	
	case 10: /* BPL */
		if(!SRBits->N) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 11: /* BMI */
		if(SRBits->N) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 12: /* BGE */
		if((SRBits->N && SRBits->V) || (!SRBits->N && !SRBits->V)) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 13: /* BLT */
		if((SRBits->N && !SRBits->V) || (!SRBits->N && SRBits->V)) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 14: /* BGT */
		if((SRBits->N && SRBits->V && !SRBits->Z) || (!SRBits->N && !SRBits->V && !SRBits->Z)) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;
	case 15: /* BLE */
		if((SRBits->Z) || (SRBits->N && !SRBits->V) || (!SRBits->N && SRBits->V)) {
			goto i_bcc_branch_taken;
		}
		goto i_bcc_branch_not_taken;

	default:
		SKYEYE_ERR("Unknown Condition Code 0x%02x\n", Instr.Bits.Condition);
		break;
	}
	SKYEYE_ERR("This should NOT happen!\n");
	return;
	/* Set the new PC */
i_bcc_branch_taken:
	cycle(BCCTime[ (Displacement > 0) ? 2 : 0 ]);
i_bcc_do_branch:
	memory_core.pc=ReferencePC+Displacement;
	return;

i_bcc_branch_not_taken:
	cycle(BCCTime[ (Displacement > 0) ? 3 : 1 ]);
	return;
}


static int disassemble(char *Instruction, char *Arg1, char *Arg2)
{
	unsigned int ReferencePC=memory_core.pc+2;
	unsigned int Displacement;
	BCC_Instr Instr;
	Memory_RetrWordFromPC(&Instr.Code);
	Displacement=Instr.Bits.Displacement;
	switch(Instr.Bits.Condition) {
	case 0: /* BRA */
		sprintf(Instruction, "BRA");
		break;
	case 1: /* BSR */
		sprintf(Instruction, "BSR");
		break;
	case 2: /* BHI */
		sprintf(Instruction, "BHI");
		break;
	case 3: /* BLS */
		sprintf(Instruction, "BLS");
		break;
	case 4: /* BCC */
		sprintf(Instruction, "BCC");
		break;
	case 5: /* BCS */
		sprintf(Instruction, "BCS");
		break;
	case 6: /* BNE */
		sprintf(Instruction, "BNE");
		break;
	case 7: /* BEQ */
		sprintf(Instruction, "BEQ");
		break;
	case 8: /* BVC */
		sprintf(Instruction, "BVC");
		break;
	case 9: /* BVS */
		sprintf(Instruction, "BVS");
		break;
	case 10: /* BPL */
		sprintf(Instruction, "BPL");
		break;
	case 11: /* BMI */
		sprintf(Instruction, "BMI");
		break;
	case 12: /* BGE */
		sprintf(Instruction, "BGE");
		break;
	case 13: /* BLT */
		sprintf(Instruction, "BLT");
		break;
	case 14: /* BGT */
		sprintf(Instruction, "BGT");
		break;
	case 15: /* BLE */
		sprintf(Instruction, "BLE");
		break;
	}

	if(Displacement==0) {
		Memory_RetrWordFromPC(&Displacement);
		Displacement = (short)Displacement;
/*		sprintf(&Instruction[3], ".W");*/
	}
/*	else
		sprintf(&Instruction[3], ".B");*/
	sprintf(Arg1, "0x%08lX", ReferencePC+Displacement);
	Arg2[0]=0;	
	return 0;
}

int bcc_5206_register(void)
{
	instruction_register(0x6000, 0xF000, &execute, &disassemble);
	return 3;
}