Subversion Repositories rf6809

; ============================================================================
;        __
;   \\__/ o\    (C) 2022  Robert Finch, Waterloo
;    \  __ /    All rights reserved.
;     \/_//     robfinch<remove>@opencores.org
;       ||
;  
;
; Timer routines for a WDC6522 compatible circuit.
;
; This source file is free software: you can redistribute it and/or modify 
; it under the terms of the GNU Lesser General Public License as published 
; by the Free Software Foundation, either version 3 of the License, or     
; (at your option) any later version.                                      
;                                                                          
; This source file 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 for more details.                             
;                                                                          
; You should have received a copy of the GNU General Public License        
; along with this program.  If not, see <http://www.gnu.org/licenses/>.    
;                                                                          
; ============================================================================
;
TimerInit:
        ldd             #$61A80                                 ; compare to 400000 (100 Hz assuming 40MHz clock)
        stb             VIA+VIA_T3CMPL
        sta             VIA+VIA_T3CMPH
        clr             VIA+VIA_T3LL
        clr             VIA+VIA_T3LH
        lda             VIA+VIA_ACR                     ; set continuous mode for timer
        ora             #$100
        sta             VIA+VIA_ACR                     ; enable timer #3 interrupts
        lda             #$810
        sta             VIA+VIA_IER
        rts

TimerIRQ:
        ; Reset the edge sense circuit in the PIC
        lda             #31                                                     ; Timer is IRQ #31
        sta             IrqSource               ; stuff a byte indicating the IRQ source for PEEK()
        sta             PIC+16                                  ; register 16 is edge sense reset reg   
        lda             VIA+VIA_IFR
        bpl             notTimerIRQ
        bita    #$800
        beq             notTimerIRQ
        clr             VIA+VIA_T3LL
        clr             VIA+VIA_T3LH
        inc             $E00037                                 ; update timer IRQ screen flag
notTimerIRQ:
        rts