;---------------------------------------------------------------------
;                                    ;16位*16位乘法子程序
;時間：2004年7月
;單位: 上海凌陽科技
;作者：周俊峰
;Email:zhoujf@sunplus.com.cn
;Tel:021-50804488 ext.6124
;
;                                    ;16位*16位乘法子程序         
;入口參數：G_Faciend_Buffer,G_Faciend_Buffer+1
;          G_Multiplier_Buffer,G_Multiplier_Buffer+1
;
;出口參數：G_Mul_Result,G_Mul_Result+1,G_Mul_Result+2,G_Mul_Result+3
;----------------------------------------------------------------------
.SYNTAX  6502   ;process standard 6502 addressing syntax
.LINKLIST       ;generate linklist information
.SYMBOLS        ;generate symbolic debug information
.PAGE0          ;define values in the range from 00h to FFh
.include        SPMC810A.inc
ORG     $80
G_Faciend_Buffer                  DS                 2;被乘數
G_Multiplier_Buffer               DS                 2;乘數
G_Mul_Result                      DS                 4;結果
G_LoopTimes                       DS                 1
.CODE
ORG     $EE00		         				
.PUBLIC		V_Reset
V_Reset:
V_PowerOn:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
						sei
						ldx 	#C_STACK_BOTTOM ;set stack bottom
						txs                	; transfer x to  stack                        
;======================================================================                   
                        lda     #B8H
                        sta     G_Faciend_Buffer;裝入被乘數低位數據
                        lda     #0BH
                        sta     G_Faciend_Buffer+1;裝入被乘數高位數據                        
                        
                        lda     #B8H
                		sta     G_Multiplier_Buffer;裝入乘數低位數據
                		lda     #0BH
                		sta     G_Multiplier_Buffer+1;裝入乘數高位數據
                		
                		lda     #0;清除結果單元
                		sta     G_Mul_Result
                		sta     G_Mul_Result+1
                		sta     G_Mul_Result+2
                        sta     G_Mul_Result+3                      
                        
                        lda		#16
	                    sta		G_LoopTimes	;set loop times 
	                                    
	                    	
L_Mul_Loop:
    					clc
						rol		G_Multiplier_Buffer 	;乘數向左移一位，判斷最高位是‘0’還是‘1’ 
    					rol     G_Multiplier_Buffer+1    
    
						bcc		L_Maximal_Bit0       ;c=0 ;if C is not "1" jump to L_Maximal_Bit0
	
L_Maximal_Bit1:  	;結果加上faciend被乘數;32位加16位數
						clc							
						lda		G_Mul_Result
						adc		G_Faciend_Buffer     
						sta     G_Mul_Result
	
						lda     G_Mul_Result+1
						adc     G_Faciend_Buffer+1
						sta     G_Mul_Result+1
	
	
	
						lda     G_Mul_Result+2;加進位
						adc     #0
						sta     G_Mul_Result+2
	
						lda     G_Mul_Result+3;加進位
						adc     #0
						sta     G_Mul_Result+3
	
L_Maximal_Bit0:	 ;left move the result directly
						clc
						rol		G_Mul_Result
						rol		G_Mul_Result+1
    					rol     G_Mul_Result+2
    					rol     G_Mul_Result+3    
	
						dec		G_LoopTimes
						lda		G_LoopTimes
						bne		L_Mul_Loop 
						
						;right move the result
						clc
						ror     G_Mul_Result+3
						ror     G_Mul_Result+2    
						ror     G_Mul_Result+1
						ror     G_Mul_Result
						
						
						
						
;========================================================================						
						
MainLoop: 

                        nop
                        nop
                        nop
                        lda    G_Mul_Result
                        lda    G_Mul_Result+1
                        lda    G_Mul_Result+2
                        lda    G_Mul_Result+3
                        nop
                        nop
                        nop
                        jmp    MainLoop 
;=============================================================================
;    Interrupt   Subroutine
;=============================================================================				
V_IRQ:
		PHA
		TXA
		PHA

IRQ_END:
		PLA
		TAX
		PLA
		RTI
;=====================================================
;Description: 	NMI Interrupt Vector
;=====================================================
.PUBLIC	V_NMI
V_NMI:
		RTI
.ORG	$1FFA					;Define	two different areas since SICE
		DW	V_NMI				;FMay download program emulated	either
		DW	V_PowerOn			;FIn internal memory or	external memory
		DW	V_IRQ

.ORG	$7FFA					;For EPROM with	EV BRD.	IRQ. CPU, or EXT. CPU
		DW	V_NMI
		DW	V_PowerOn
		DW	V_IRQ

.ORG	$FFFA					;For ICE trace.
		DW	V_NMI
		DW	V_PowerOn
		DW	V_IRQ  		
.END