initial commit

Makefile

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+CC65    =       $(HOME)/trees/cc65/bin/
+CPU     =       6502
+
+a.out: main.o interrupt.o vectors.o apple2rom.cfg apple2rom.lib
+	$(CC65)/ld65 -C apple2rom.cfg -m main.map --dbgfile main.dbg interrupt.o vectors.o main.o apple2rom.lib
+
+clean:
+	rm *.o a.out main.s
+
+main.s: main.c
+	$(CC65)/cc65 -t none -O --cpu $(CPU) main.c
+
+main.o: main.s
+	$(CC65)/ca65 --cpu $(CPU) main.s
+
+interrupt.o: interrupt.s
+	$(CC65)/ca65 --cpu $(CPU) interrupt.s
+
+vectors.o: vectors.s
+	$(CC65)/ca65 --cpu $(CPU) vectors.s
+
+crt0.o: crt0.s
+	$(CC65)/ca65 --cpu $(CPU) crt0.s
+
+apple2rom.lib: crt0.o
+	../cc65/bin/ar65 a apple2rom.lib crt0.o

apple2rom.cfg

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+MEMORY {
+    ZP:        start =    $0, size =  $100, type   = rw, define = yes;
+    RAM:       start =  $4000, size = $4000, define = yes;
+    ROM:       start = $D000, size = $3000, file   = %O;
+}
+
+SEGMENTS {
+    ZEROPAGE: load = ZP,  type = zp,  define   = yes;
+    DATA:     load = ROM, type = rw,  define   = yes, run = RAM;
+    BSS:      load = RAM, type = bss, define   = yes;
+    HEAP:     load = RAM, type = bss, optional = yes;
+    STARTUP:  load = ROM, type = ro;
+    ONCE:     load = ROM, type = ro,  optional = yes;
+    CODE:     load = ROM, type = ro;
+    RODATA:   load = ROM, type = ro;
+    VECTORS:  load = ROM, type = ro,  start    = $FFFA;
+}
+
+FEATURES {
+    CONDES:    segment = STARTUP,
+               type    = constructor,
+               label   = __CONSTRUCTOR_TABLE__,
+               count   = __CONSTRUCTOR_COUNT__;
+    CONDES:    segment = STARTUP,
+               type    = destructor,
+               label   = __DESTRUCTOR_TABLE__,
+               count   = __DESTRUCTOR_COUNT__;
+}
+
+SYMBOLS {
+    # Define the stack size for the application
+    __STACKSIZE__:  value = $0200, type = weak;
+    # __STACKSIZE__: type = weak, value = $0800; # 2k stack
+}
+

crt0.s

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+; ---------------------------------------------------------------------------
+; crt0.s
+; ---------------------------------------------------------------------------
+;
+; Startup code for cc65 (Single Board Computer version)
+
+.export   _init, _exit
+.import   _main
+
+.export   __STARTUP__ : absolute = 1        ; Mark as startup
+.import   __RAM_START__, __RAM_SIZE__       ; Linker generated
+
+.import    copydata, zerobss, initlib, donelib
+
+.include  "zeropage.inc"
+
+; ---------------------------------------------------------------------------
+; Place the startup code in a special segment
+
+.segment  "STARTUP"
+
+; ---------------------------------------------------------------------------
+; A little light 6502 housekeeping
+
+_init:    LDX     #$FF                 ; Initialize stack pointer to $01FF
+          TXS
+          CLD                          ; Clear decimal mode
+
+; ---------------------------------------------------------------------------
+; Set cc65 argument stack pointer
+
+          LDA     #<(__RAM_START__ + __RAM_SIZE__)
+          STA     sp
+          LDA     #>(__RAM_START__ + __RAM_SIZE__)
+          STA     sp+1
+
+; ---------------------------------------------------------------------------
+; Initialize memory storage
+
+          JSR     zerobss              ; Clear BSS segment
+          JSR     copydata             ; Initialize DATA segment
+          JSR     initlib              ; Run constructors
+
+; ---------------------------------------------------------------------------
+; Call main()
+
+          JSR     _main
+
+; ---------------------------------------------------------------------------
+; Back from main (this is also the _exit entry):  force a software break
+
+_exit:    JSR     donelib              ; Run destructors
+          BRK
+

interrupt.s

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+; ---------------------------------------------------------------------------
+; interrupt.s
+; ---------------------------------------------------------------------------
+;
+; Interrupt handler.
+;
+; Checks for a BRK instruction and returns from all valid interrupts.
+
+.import   _stop
+.export   _irq_int, _nmi_int
+
+.segment  "CODE"
+
+.PC02                             ; Force 65C02 assembly mode
+
+; ---------------------------------------------------------------------------
+; Non-maskable interrupt (NMI) service routine
+
+_nmi_int:  RTI                    ; Return from all NMI interrupts
+
+; ---------------------------------------------------------------------------
+; Maskable interrupt (IRQ) service routine
+
+_irq_int:  PHX                    ; Save X register contents to stack
+           TSX                    ; Transfer stack pointer to X
+           PHA                    ; Save accumulator contents to stack
+           INX                    ; Increment X so it points to the status
+           INX                    ;   register value saved on the stack
+           LDA $100,X             ; Load status register contents
+           AND #$10               ; Isolate B status bit
+           BNE break              ; If B = 1, BRK detected
+
+; ---------------------------------------------------------------------------
+; IRQ detected, return
+
+irq:       PLA                    ; Restore accumulator contents
+           PLX                    ; Restore X register contents
+           RTI                    ; Return from all IRQ interrupts
+
+; ---------------------------------------------------------------------------
+; BRK detected, stop
+
+break:     JMP break              ; If BRK is detected, something very bad
+                                  ;   has happened, so stop running
+

main.c

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+char *title = "Apple IIa";
+unsigned char title_length = 9;
+
+unsigned char *text_page1_base = (unsigned char *)0x400;
+
+int main(void)
+{
+    int offset = (80 - title_length) / 2;
+
+    unsigned char *loc = text_page1_base + offset;
+
+    int i;
+
+    for(i = 0; i < 80 * 24; i++)
+        text_page1_base[i] = ' ' | 0x80;
+
+    for(i = 0; i < title_length; i++)
+        loc[i] = title[i] | 0x80;
+
+    while(1);
+}

vectors.s

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+; ---------------------------------------------------------------------------
+; vectors.s
+; ---------------------------------------------------------------------------
+;
+; Defines the interrupt vector table.
+
+.import    _init
+.import    _nmi_int, _irq_int
+
+.segment  "VECTORS"
+
+.addr      _nmi_int    ; NMI vector
+.addr      _init       ; Reset vector
+.addr      _irq_int    ; IRQ/BRK vector
+