Reduce flicker by waiting for horizontal retrace before switching ROM and

CHARGEN. Can be disabled by setting USEWSYNC to 0.

diff --git a/libsrc/atari/shadow_ram_handlers.s b/libsrc/atari/shadow_ram_handlers.s
index adf9085b1a8a82a5cafa7cfe3bf297ffbb31c7e7..e9b682cf174f3bcce198628181aa34e5907bccc7 100644 (file)
--- a/libsrc/atari/shadow_ram_handlers.s
+++ b/libsrc/atari/shadow_ram_handlers.s
@@ -5,6 +5,7 @@
 ;
 
 DEBUG  =       1
+USEWSYNC=      1
 CHKBUF =       1       ; check if bounce buffering is needed (bounce buffering is always done if set to 0)
 
 .if .defined(__ATARIXL__)
@@ -24,7 +25,22 @@ CHKBUF       =       1       ; check if bounce buffering is needed (bounce buffering is always don
 BUFSZ          =       128             ; bounce buffer size
 BUFSZ_SIO      =       256
 
+.macro wsync
+.if USEWSYNC
+       sta     WSYNC
+.endif
+.endmacro
+
 .macro disable_rom
+       lda     PORTB
+       and     #$fe
+       wsync
+       sta     PORTB
+       lda     #>__CHARGEN_START__
+       sta     CHBAS
+       sta     CHBASE
+.endmacro
+.macro disable_rom_quick
        lda     PORTB
        and     #$fe
        sta     PORTB
@@ -32,7 +48,25 @@ BUFSZ_SIO    =       256
        sta     CHBAS
        sta     CHBASE
 .endmacro
+.macro disable_rom_val val
+       lda     val
+       wsync
+       sta     PORTB
+       lda     #>__CHARGEN_START__
+       sta     CHBAS
+       sta     CHBASE
+.endmacro
+
 .macro enable_rom
+       lda     PORTB
+       ora     #1
+       wsync
+       sta     PORTB
+       lda     #$E0
+       sta     CHBAS
+       sta     CHBASE
+.endmacro
+.macro enable_rom_quick
        lda     PORTB
        ora     #1
        sta     PORTB
@@ -48,9 +82,9 @@ BUFSZ_SIO     =       256
 sram_init:
 
 ; disable all interrupts
-       sei
        ldx     #0
        stx     NMIEN           ; disable NMI
+       sei
 
 ; disable ROMs
        disable_rom
@@ -72,9 +106,9 @@ sram_init:
        sta     $fffb
 
 ; enable interrupts
+       cli
        lda     #$40
        sta     NMIEN
-       cli
 
        rts
 
@@ -104,14 +138,14 @@ bounce_buffer:    .res    BUFSZ_SIO
 .macro int_wrap orgvec
        .local  ret
        pha
-       enable_rom
+       enable_rom_quick
        lda     #>ret
        pha
        lda     #<ret
        pha
        php
        jmp     (orgvec)
-ret:   disable_rom
+ret:   disable_rom_quick
        pla
        rti
 .endmacro
@@ -209,26 +243,6 @@ CIO_filename2:
        jmp     CIO_fn_cont
 
 
-; enable ROM, call CIO, disable ROM
-
-CIO_call_a:
-       lda     CIO_a
-
-CIOV_call:
-       pha
-       lda     PORTB
-       sta     cur_CIOV_PORTB
-       enable_rom
-       pla
-       jsr     CIOV_org
-       php
-       pha
-       lda     cur_CIOV_PORTB
-       sta     PORTB
-       pla
-       plp
-       rts
-
 
 ; CIO handler
 ; We have buffer pointer and length entries in the IOCB, but their
@@ -264,6 +278,28 @@ CIO_handler:
        bcs     CIO_call_a              ; other commands: assume no buffer
 ; not reached
 
+; enable ROM, call CIO, disable ROM
+
+CIO_call_a:
+       lda     CIO_a
+
+CIOV_call:
+       pha
+       lda     PORTB
+       sta     cur_CIOV_PORTB
+       enable_rom
+       pla
+       jsr     CIOV_org
+       php
+       pha
+       disable_rom_val cur_CIOV_PORTB
+;      lda     cur_CIOV_PORTB
+;      sta     PORTB
+       pla
+       plp
+       rts
+
+
 CIO_write_jmp:
        jmp     CIO_write
 
@@ -859,8 +895,9 @@ SIO_call:
        jsr     SIOV_org
        php
        pha
-       lda     cur_SIOV_PORTB
-       sta     PORTB
+       disable_rom_val cur_SIOV_PORTB
+;      lda     cur_SIOV_PORTB
+;      sta     PORTB
        pla
        plp
        rts
@@ -933,7 +970,7 @@ SIO_write:
        bcs     sio_write_len_ok
 
        lda     #DERROR         ; don't know a better status code for this
-       bne     SIO_err
+       jmp     SIO_err
 
 sio_write_len_ok:
        lda     DBUFLO
@@ -1080,8 +1117,9 @@ KEYBDV_handler:
         pha
        rts             ; call keyboard handler
 kret:  pha
-       lda     cur_KEYBDV_PORTB
-       sta     PORTB
+       disable_rom_val cur_KEYBDV_PORTB
+;      lda     cur_KEYBDV_PORTB
+;      sta     PORTB
        pla
        rts
 
@@ -1097,8 +1135,9 @@ SETVBV_handler:
        jsr     SETVBV_org
        php
        pha
-       lda     cur_SETVBV_PORTB
-       sta     PORTB
+       disable_rom_val cur_SETVBV_PORTB
+;      lda     cur_SETVBV_PORTB
+;      sta     PORTB
        pla
        plp
        rts