Atari: fix interrupt handling if extended memory is banked in

Extendend memory is mapped over the main memory in the 0x4000..0x7FFF
area. Many DOSes disable interrupts while extended memory is banked in,
but not all (e.g. SpartaDOS-X).
This change modifies the initial interrupt handler to map in main memory
before chaining to the "worker" handlers.
Since the initial interrupt handler uses a data segment to store the
trampoline to chain to the original handler, introduce a new "LOWBSS"
segment to hold this trampoline. Otherwise the trampoline may end up
inside the 0x4000..0x7FFF area.

Add a link time warning if "LOWCODE" segment lays within the extended
memory window.

diff --git a/cfg/atari-cart.cfg b/cfg/atari-cart.cfg
index 31d2cb1b97ec93a9554a14c666b9148d6318db15..16208f90d9b0977a406e392ec94a1aae74217e45 100644 (file)
--- a/cfg/atari-cart.cfg
+++ b/cfg/atari-cart.cfg
@@ -10,23 +10,25 @@ SYMBOLS {
     __CARTFLAGS__:       type = weak,   value = $01;   # see documentation for other possible values
 }
 MEMORY {
-    ZP:     file = "", define = yes, start = $0082,                size = $007E;
-    MAIN:   file = "", define = yes, start = %S,                   size = __CARTSIZE__;
-    ROM:    file = %O, define = yes, start = $C000 - __CARTSIZE__, size = __CARTSIZE__ - 6, fill = yes, fillval = $FF;
-    CARTID: file = %O,               start = $BFFA,                size = $0006;
+    ZP:      file = "", define = yes, start = $0082,                size = $007E;
+    MAIN:    file = "", define = yes, start = %S,                   size = __CARTSIZE__;
+    ROM:     file = %O, define = yes, start = $C000 - __CARTSIZE__, size = __CARTSIZE__ - 6, fill = yes, fillval = $FF;
+    CARTID:  file = %O,               start = $BFFA,                size = $0006;
+    DISCARD: file = "",               start = $0100,                size = $FF00;
 }
 SEGMENTS {
-    ZEROPAGE: load = ZP,              type = zp,                optional = yes;
-    EXTZP:    load = ZP,              type = zp,                optional = yes;
-    STARTUP:  load = ROM,             type = ro,  define = yes, optional = yes;
-    LOWCODE:  load = ROM,             type = ro,  define = yes, optional = yes;
-    ONCE:     load = ROM,             type = ro,                optional = yes;
-    CODE:     load = ROM,             type = ro,  define = yes;
-    RODATA:   load = ROM,             type = ro,                optional = yes;
-    DATA:     load = ROM, run = MAIN, type = rw,  define = yes, optional = yes;
-    INIT:     load = MAIN,            type = bss,               optional = yes;
-    BSS:      load = MAIN,            type = bss, define = yes, optional = yes;
-    CARTHDR:  load = CARTID,          type = ro;
+    ZEROPAGE: load = ZP,                  type = zp,                optional = yes;
+    EXTZP:    load = ZP,                  type = zp,                optional = yes;
+    STARTUP:  load = ROM,                 type = ro,  define = yes, optional = yes;
+    LOWBSS:   load = DISCARD, run = MAIN, type = rw,                optional = yes;  # not zero-initialized
+    LOWCODE:  load = ROM,                 type = ro,  define = yes, optional = yes;
+    ONCE:     load = ROM,                 type = ro,                optional = yes;
+    CODE:     load = ROM,                 type = ro,  define = yes;
+    RODATA:   load = ROM,                 type = ro,                optional = yes;
+    DATA:     load = ROM, run = MAIN,     type = rw,  define = yes, optional = yes;
+    INIT:     load = MAIN,                type = bss,               optional = yes;
+    BSS:      load = MAIN,                type = bss, define = yes, optional = yes;
+    CARTHDR:  load = CARTID,              type = ro;
 }
 FEATURES {
     CONDES: type    = constructor,

diff --git a/cfg/atari-cassette.cfg b/cfg/atari-cassette.cfg
index 5e99c303e8bcff3c4648142aa66236940a36cec3..465add95e3bc809a7943c8f143908dfc4646e650 100644 (file)
--- a/cfg/atari-cassette.cfg
+++ b/cfg/atari-cassette.cfg
@@ -16,6 +16,7 @@ SEGMENTS {
     EXTZP:    load = ZP,   type = zp,                optional = yes;
     CASHDR:   load = MAIN, type = ro;
     STARTUP:  load = MAIN, type = ro,  define = yes, optional = yes;
+    LOWBSS:   load = MAIN, type = rw,                optional = yes;  # not zero-initialized
     LOWCODE:  load = MAIN, type = ro,  define = yes, optional = yes;
     ONCE:     load = MAIN, type = ro,                optional = yes;
     CODE:     load = MAIN, type = ro,  define = yes;

diff --git a/cfg/atari-overlay.cfg b/cfg/atari-overlay.cfg
index 87e62d7648936db308695de14d71e4f41f4426d4..fdf2e983c63e412f922c7fc0f90e4248fe21cb6a 100644 (file)
--- a/cfg/atari-overlay.cfg
+++ b/cfg/atari-overlay.cfg
@@ -46,6 +46,7 @@ SEGMENTS {
     SYSCHKTRL: load = SYSCHKTRL,  type = ro,                optional = yes;
     MAINHDR:   load = MAINHDR,    type = ro;
     STARTUP:   load = MAIN,       type = ro,  define = yes;
+    LOWBSS:    load = MAIN,       type = rw,                optional = yes;  # not zero-initialized
     LOWCODE:   load = MAIN,       type = ro,  define = yes, optional = yes;
     ONCE:      load = MAIN,       type = ro,                optional = yes;
     CODE:      load = MAIN,       type = ro,  define = yes;

diff --git a/cfg/atari.cfg b/cfg/atari.cfg
index 4680a89edb0537cefb773d053171f75a1d43ae5e..9e0ea474fc62a41930bc89ad53145f3ebfe5fdff 100644 (file)
--- a/cfg/atari.cfg
+++ b/cfg/atari.cfg
@@ -34,6 +34,7 @@ SEGMENTS {
     SYSCHKTRL: load = SYSCHKTRL,  type = ro,                optional = yes;
     MAINHDR:   load = MAINHDR,    type = ro;
     STARTUP:   load = MAIN,       type = ro,  define = yes;
+    LOWBSS:    load = MAIN,       type = rw,                optional = yes;  # not zero-initialized
     LOWCODE:   load = MAIN,       type = ro,  define = yes, optional = yes;
     ONCE:      load = MAIN,       type = ro,                optional = yes;
     CODE:      load = MAIN,       type = ro,  define = yes;

diff --git a/cfg/atarixl-largehimem.cfg b/cfg/atarixl-largehimem.cfg
index 56d2af15bbbdcf6d3e57ec195f1087e87039e275..842a485a1a8821c25a554cf2fb697ebac090791e 100644 (file)
--- a/cfg/atarixl-largehimem.cfg
+++ b/cfg/atarixl-largehimem.cfg
@@ -61,6 +61,7 @@ SEGMENTS {
 
     MAINHDR:     load = MAINHDR,                      type = ro;
     STARTUP:     load = MAIN,                         type = ro,  define = yes;
+    LOWBSS:      load = MAIN,                         type = rw,                optional = yes;  # not zero-initialized
     LOWCODE:     load = MAIN,                         type = ro,  define = yes, optional = yes;
     ONCE:        load = MAIN,                         type = ro,                optional = yes;
     CODE:        load = MAIN,                         type = ro,  define = yes;

diff --git a/cfg/atarixl-overlay.cfg b/cfg/atarixl-overlay.cfg
index 923436497558b77768bae748419c37b8d78291b9..f3a40b6a73c18b468f7bb96949ffaebc9577f8f6 100644 (file)
--- a/cfg/atarixl-overlay.cfg
+++ b/cfg/atarixl-overlay.cfg
@@ -72,6 +72,7 @@ SEGMENTS {
 
     MAINHDR:     load = MAINHDR,                       type = ro;
     STARTUP:     load = MAIN,                          type = ro,  define = yes;
+    LOWBSS:      load = MAIN,                          type = rw,                optional = yes;  # not zero-initialized
     LOWCODE:     load = MAIN,                          type = ro,  define = yes, optional = yes;
     ONCE:        load = MAIN,                          type = ro,                optional = yes;
     CODE:        load = MAIN,                          type = ro,  define = yes;

diff --git a/cfg/atarixl.cfg b/cfg/atarixl.cfg
index 197daace6a67b18fc9a4b4b38c32b72e8edf1b36..c2d331fab793c6a1e7e2f30af420f53eec704736 100644 (file)
--- a/cfg/atarixl.cfg
+++ b/cfg/atarixl.cfg
@@ -59,6 +59,7 @@ SEGMENTS {
 
     MAINHDR:     load = MAINHDR,                       type = ro;
     STARTUP:     load = MAIN,                          type = ro,  define = yes;
+    LOWBSS:      load = MAIN,                          type = rw,                optional = yes;  # not zero-initialized
     LOWCODE:     load = MAIN,                          type = ro,  define = yes, optional = yes;
     ONCE:        load = MAIN,                          type = ro,                optional = yes;
     CODE:        load = MAIN,                          type = ro,  define = yes;

diff --git a/libsrc/atari/crt0.s b/libsrc/atari/crt0.s
index d14567491cb40e44069e2cb310e5350af2c3016d..97b7d7e95df3f344e66f5047770ecda27f1a0750 100644 (file)
--- a/libsrc/atari/crt0.s
+++ b/libsrc/atari/crt0.s
@@ -15,6 +15,7 @@
         .import         callmain, zerobss
         .import         __RESERVED_MEMORY__
         .import         __MAIN_START__, __MAIN_SIZE__
+        .import         __LOWCODE_RUN__, __LOWCODE_SIZE__
 .ifdef __ATARIXL__
         .import         __STACKSIZE__
         .import         sram_init
@@ -199,3 +200,11 @@ LMARGN_save:    .res    1
 .ifndef __ATARIXL__
 APPMHI_save:    .res    2
 .endif
+
+; ------------------------------------------------------------------------
+
+.segment "LOWCODE"       ; have at least one (empty) segment of LOWCODE, so that the next line works even if the program doesn't make use of this segment
+.assert (__LOWCODE_RUN__ + __LOWCODE_SIZE__ <= $4000 || __LOWCODE_RUN__ > $7FFF || __LOWCODE_SIZE__ = 0), warning, "'lowcode area' reaches into $4000..$7FFF bank memory window"
+; check for LOWBSS_SIZE = 0 not needed since the only file which uses LOWBSS (irq.s) also uses LOWCODE
+; check for LOWCODE_RUN > $7FFF is mostly for cartridges, where this segment is loaded high (into cart ROM)
+; there is a small chance that if the user loads the program really high, LOWCODE is above $7FFF, but LOWBSS is below -- no warning emitted in this case

diff --git a/libsrc/atari/irq.s b/libsrc/atari/irq.s
index 1878ea0a2bd0e35df46a9a5e783c3330fddb925b..86fef609b3044861a2294c7b75bd93a986f4d262 100644 (file)
--- a/libsrc/atari/irq.s
+++ b/libsrc/atari/irq.s
@@ -16,6 +16,8 @@
 .segment        "ONCE"
 
 initirq:
+        lda     #$4C                    ; JMP opcode
+        sta     IRQInd
         lda     VVBLKD
         ldx     VVBLKD+1
         sta     IRQInd+1
@@ -45,17 +47,22 @@ IRQStub:
 .ifdef CHARGEN_RELOC
         lda     CHBAS
         pha
+.endif
 .endif
         lda     PORTB
         pha
-        and     #$FE
-        sta     PORTB                   ; disable ROM
+.ifdef __ATARIXL__
+        and     #$FE                    ; disable ROM
+.endif
+        ora     #$10                    ; map main memory into $4000..$7FFF area
+        sta     PORTB
+.ifdef __ATARIXL__
         set_chbase >__CHARGEN_START__
 .endif
         jsr     callirq                 ; Call the functions
-.ifdef __ATARIXL__
         pla
-        sta     PORTB                   ; restore old ROM setting
+        sta     PORTB                   ; restore old memory settings
+.ifdef __ATARIXL__
 .ifdef CHARGEN_RELOC
         pla
         sta     CHBAS
@@ -66,6 +73,8 @@ IRQStub:
 
 ; ------------------------------------------------------------------------
 
-.data
+.segment        "LOWBSS"
+
+IRQInd: .res    3
 
-IRQInd: jmp     $0000
+.end