; **************************************************************************************************
; **************************************************************************************************
;  THIS WILL NOT RUN ON REAL HARDWARE UNLESS YOU BURN THE NATIVE CODE AT THE BOTTOM
;  OF THIS FILE INTO THE GIGATRONS ROM AT THE CORRECT ADDRESS, EMULATION ONLY!
; **************************************************************************************************
; **************************************************************************************************

vram        EQU     0x0800
REENTER     EQU     0x03CB
sysFn       EQU     0x22 

i           EQU     0x30
j           EQU     0x31
vbase       EQU     0x40

                                        
SYS_ClearRow32_56   EQU     0x2300      ; clear 32 pixels at a time, native code that is defined with either DBR or DWR is written to ROM at this address

                                        
            LDWI    vram
            STW     vbase       ; vram base address
            
            LDWI    SYS_ClearRow32_56   ; clears 32 row pixels at a time
            STW     sysFn

clear       SYS     56
            LDWI    0x0020
            ADDW    vbase
            STW     vbase
            LD      vbase+1
            SUBI    0x7F
            BLT     clear
            LDI     0x08        ; finish off last row
            ST      i
last_row    SYS     56
            LDWI    0x0020
            ADDW    vbase
            STW     vbase
            LD      i
            SUBI    0x01
            ST      i
            BGT     last_row
            
loop        BRA     loop


; these are native code routines that are written into ROM using the DBR command, (Define Byte ROM), at the equate defined
; above: this native code is specific to this vCPU asm module with the input registers that it accepts
;SYS_ClearRow32_56       DBR $11 $40 $15 $41 $00 $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00
;                        DBR $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00
;                        DBR $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00
;                        DBR $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $DE $00 $14 $03 $E0 $CB $00 $E4

SYS_ClearRow32_56       .LD     [0x40],X
                        .LD     [0x41],Y
                        .LD     0x00
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .ST     [Y,X++]
                        .NOP                ; pad instructions so odd(14 + number of instructions) = true

                        .LD     REENTER >>8,y
                        .JMP    y,REENTER
                        .LD     0xE4        ; 0 - ((14 + number of instructions + 3) / 2), odd(14 + number of instructions) = true