New SplitBit programs.

Programs/testPrograms/dataPointerTest.asm

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+; Tests the Data Pointer calling convention.
+;
+; Every Data Pointer is aimed at a different marker byte, then a subroutine
+; repoints all four of them at Z and returns.
+;
+; DP0 through DP2 are preserved across a CALL, so they should come back still
+; aimed at their own markers. DP3 is volatile, which is what lets a subroutine
+; hand an address back to its caller, so it should come back aimed at Z.
+;
+; Correct output is ABCZ.
+
+#Program
+
+start:
+  SETD.0 MarkA
+  SETD.1 MarkB
+  SETD.2 MarkC
+  SETD.3 MarkD
+  CALL clobber
+
+  ; Read a byte through each pointer in turn and print it.
+  LDA.0
+  OUTA 0x00
+  LDA.1
+  OUTA 0x00
+  LDA.2
+  OUTA 0x00
+  LDA.3
+  OUTA 0x00
+
+  INIA 0x0A
+  OUTA 0x00
+  HALT
+
+clobber:
+  ; Aim every pointer somewhere else. Only the change to DP3 should outlive the RET.
+  SETD.0 MarkZ
+  SETD.1 MarkZ
+  SETD.2 MarkZ
+  SETD.3 MarkZ
+  RET
+
+#Data
+
+MarkA:
+"A"
+MarkB:
+"B"
+MarkC:
+"C"
+MarkD:
+"D"
+MarkZ:
+"Z"