Initial data commit

Task/Call-a-foreign-language-function/68000-Assembly/call-a-foreign-language-function-1.68000

@@ -0,0 +1,30 @@
+org &0000 ;execution resets here after the 68000 resets the Z80 and sends a bus request.
+jr start
+
+org &0038 ;in IM 1 mode, we jump here for an IRQ. But this isn't being used for this example, so we'll just silently return.
+reti
+
+org &0060
+start:
+DI
+IM 1
+LD SP,&2000
+
+
+main:         ;hardware non-maskable interrupt (NMI) jumps here (address &0066)
+
+ld a,(&1F00)  ;we'll only allow the 68000 to alter the contents of this memory address.
+or a
+jr z,main     ;just keep looping until it's nonzero.
+
+;by counting the bytes each instruction takes, it can be proven that this label points to &006C.
+;The call opcode takes 1 byte and the operand that follows takes two bytes.
+
+smc:
+call &0000    ;we'll overwrite the operand at &006D-&006E with whatever function we want to call.
+
+done:
+jp done       ;loop until next reset
+
+ExampleFunction:   ;ADDR: &0072($A00072)
+ret                ;for simplicity this does nothing but in reality you'd have it do something sound-related here.

Task/Call-a-foreign-language-function/68000-Assembly/call-a-foreign-language-function-2.68000

@@ -0,0 +1,16 @@
+Z80_Call:
+MOVE.W #$100,$A11100  ;write: z80 reset
+.wait:
+BTST #8,$A11100       ;read: check bit 8 to see if the z80 is busy
+BNE .wait             ;loop until not busy
+
+
+;now we write the function address
+;z80 is little-endian so we need to reverse the byte order.
+;also 68000 cannot safely write words at odd addresses so we need to write as bytes.
+
+MOVE.B #$72,$A0006D
+MOVE.B #$00,$A0006E  ;this changes the "call &0000" above to "call ExampleFunction"
+
+MOVE.B #$FF,$A01F01  ;unlock the semaphore
+MOVE.W #0,$A11100    ;Z80 Bus Request - after this write, the Z80 will start executing code.