Top Level Namespace

Includes:
Asm6502

Defined Under Namespace

Modules: Asm6502

Constant Summary collapse

TIA_BASE_ADDRESS = 
0
TIA_BASE_READ_ADDRESS = 
TIA_BASE_ADDRESS
TIA_BASE_WRITE_ADDRESS = 
TIA_BASE_ADDRESS
VERSION_MACRO =

MACRO.H Version 1.06, 3/SEPTEMBER/2004

106

Instance Method Summary collapse

Instance Method Details

#clean_start ⇒ Object

CLEAN_START Original author: Andrew Davie Standardised start-up code, clears stack, all TIA registers and RAM to 0 Sets stack pointer to $FF, and all registers to 0 Sets decimal mode off, sets interrupt flag (kind of un-necessary) Use as very first section of code on boot (ie: at reset) Code written to minimise total ROM usage - uses weird 6502 knowledge :)



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# File 'lib/asm6502/vcs/macro.rb', line 100

def clean_start
                sei
                cld

                ldx 0
                txa
                tay
Label[:CLEAR_STACK]
                dex
                txs
                pha
                bne :CLEAR_STACK     # SP=$FF, X = A = Y = 0

end

#set_pointer(pointer, address) ⇒ Object

SET_POINTER Original author: Manuel Rotschkar

Sets a 2 byte RAM pointer to an absolute address.

Usage: SET_POINTER pointer, address Example: SET_POINTER SpritePTR, SpriteData

Note: Alters the accumulator, NZ flags IN 1: 2 byte RAM location reserved for pointer IN 2: absolute address



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# File 'lib/asm6502/vcs/macro.rb', line 128

def set_pointer(pointer, address)
    LDA #<.ADDRESS  # Get Lowbyte of Address
    STA .POINTER    # Store in pointer
    LDA #>.ADDRESS  # Get Hibyte of Address
    STA .POINTER+1  # Store in pointer+1
end

#sleep(cycles) ⇒ Object

SLEEP duration Original author: Thomas Jentzsch Inserts code which takes the specified number of cycles to execute. This is useful for code where precise timing is required. ILLEGAL-OPCODE VERSION DOES NOT AFFECT FLAGS OR REGISTERS. LEGAL OPCODE VERSION MAY AFFECT FLAGS Uses illegal opcode (DASM 2.20.01 onwards).



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# File 'lib/asm6502/vcs/macro.rb', line 56

def sleep(cycles)  #usage: sleep n (n>1)
    if cycles < 2
        puts "MACRO ERROR: 'SLEEP': Duration must be > 1"
        exit 1
    end

    if cycles & 1
        bit :VSYNC
    end

    cycles -= 3

    (cycles / 2).times do
        nop
    end
end

#vertical_sync ⇒ Object

OUT: A = 0



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# File 'lib/asm6502/vcs/macro.rb', line 81

def vertical_sync
                lda 0b1110         #%1110          # each '1' bits generate a VSYNC ON line (bits 1..3)
Label[:VSLP1]
                sta :WSYNC   # 1st '0' bit resets Vsync, 2nd '0' bit exit loop
                sta :VSYNC
                lsr
                bne :VSLP1          # branch until VYSNC has been reset

end