add testprogram for _sys() function on Atari

testcode/lib/atari/sys.c

@@ -0,0 +1,37 @@
+/*
+ * testprogram for _sys() function on Atari
+ *
+ * 17-Sep-2013, chris@groessler.org
+ *
+ * uses PUTCHR IOCB function to display a string
+ */
+
+#include <atari.h>
+#include <6502.h>
+#include <conio.h>
+
+static struct regs regs;
+static struct __iocb *iocb = &IOCB;  /* use IOCB #0 */
+
+static char message[] = "I'm the sys test text\n";
+
+int main(void)
+{
+    /* setup IOCB for CIO call */
+    iocb->buffer = message;
+    iocb->buflen = sizeof(message) - 1;
+    iocb->command = IOCB_PUTCHR;
+
+    /* setup input registers */
+    regs.x = 0;         /* IOCB #0 */
+    regs.pc = 0xe456;   /* CIOV */
+
+    /* call CIO */
+    _sys(&regs);
+
+    if (regs.y != 1)
+        cprintf("CIO error 0x%02\r\n", regs.y);
+
+    cgetc();
+    return 0;
+}