Add functions for pressing/releasing keys

include/apple2.h

@@ -8,8 +8,19 @@ typedef struct {
      * The apple 2 hardware used an MOS-6502 processor.
      */
     mos6502 *cpu;
+
+    /*
+     * This is the literal memory that the CPU above will create. You
+     * should _not_ attempt to free this memory; allow the CPU's own
+     * delete function to do that.
+     */
+    vm_segment *memory;
 } apple2;
 
 extern apple2 *apple2_create();
+extern void apple2_free(apple2 *);
+extern void apple2_press_key(apple2 *, vm_8bit);
+extern void apple2_clear_strobe(apple2 *);
+extern void apple2_release_key(apple2 *);
 
 #endif

src/apple2.c

@@ -3,7 +3,23 @@
  */
 
 #include "apple2.h"
+#include "vm_segment.h"
 
+/*
+ * This is the memory address where an apple program can find the value
+ * of the key that was last pressed.
+ */
+#define LAST_KEY 0xC000
+
+/*
+ * This is the address in memory where you can find whether a key is
+ * currently pressed or not.
+ */
+#define ANY_KEY_DOWN 0xC010
+
+/*
+ * Create the basic apple2 structure.
+ */
 apple2 *
 apple2_create()
 {
@@ -15,6 +31,65 @@ apple2_create()
     }
 
     mach->cpu = mos6502_create();
+    mach->memory = mach->cpu->memory;
     
     return mach;
 }
+
+/*
+ * Free the memory reserved for an apple2 struct.
+ */
+void
+apple2_free(apple2 *mach)
+{
+    mos6502_free(mach->cpu);
+
+    // NOTE: we do _NOT_ want to clear the memory field of mach, as it's
+    // co-owned with the cpu struct that we just freed above.
+
+    free(mach);
+}
+
+void
+apple2_press_key(apple2 *mach, vm_8bit ch)
+{
+    // The apple2 can only handle ASCII values of 0 through 127.
+    // However, the eigth bit is called the "strobe" bit, and is treated
+    // specially. In particular, the strobe bit is 1 if a key was
+    // pressed down, and remains 1 until you reset it by reading from
+    // the clear-strobe location.
+    ch = ch | 0x80;
+
+    // This is the location in memory where a program will expect to
+    // find the value of the last key that was pressed.
+    vm_segment_set(mach->memory, LAST_KEY, ch);
+
+    // This area is a combination of flags; the eighth bit here is the
+    // "any-key-down" flag, which is a bit of a mouthful. It's 1 if a
+    // key is pressed, and 0 if not. The effect of reading this bit will
+    // also _clear_ the strobe bit in the $C000 address (above).
+    vm_segment_set(mach->memory, ANY_KEY_DOWN, 0x80);
+}
+
+/*
+ * This function will clear the 8th bit, which is the "strobe" bit, from
+ * the position in memory where the value of the last key that was
+ * pressed is held.
+ */
+void
+apple2_clear_strobe(apple2 *mach)
+{
+    vm_8bit ch;
+
+    ch = vm_segment_get(mach->memory, LAST_KEY);
+    vm_segment_set(mach->memory, LAST_KEY, ch & 0x7F);
+}
+
+/*
+ * This function will clear the value of the any-key-down switch/flag.
+ */
+void
+apple2_release_key(apple2 *mach)
+{
+    vm_segment_set(mach->memory, ANY_KEY_DOWN, 0);
+}

tests/apple2.c

@@ -2,11 +2,47 @@
 
 #include "apple2.h"
 
+static apple2 *mach;
+
+void
+setup()
+{
+    mach = apple2_create();
+}
+
+void
+teardown()
+{
+    apple2_free(mach);
+}
+
+TestSuite(apple2, .init = setup, .fini = teardown);
+
 Test(apple2, create)
 {
-    apple2 *mach;
-
-    mach = apple2_create();
     cr_assert_neq(mach, NULL);
     cr_assert_neq(mach->cpu, NULL);
 }
+
+Test(apple2, press_key)
+{
+    apple2_press_key(mach, 123);
+    cr_assert_eq(vm_segment_get(mach->memory, 0xC000), 123 | 0x80);
+    cr_assert_eq(vm_segment_get(mach->memory, 0xC010), 0x80);
+}
+
+Test(apple2, clear_strobe)
+{
+    apple2_press_key(mach, 123);
+    cr_assert_eq(vm_segment_get(mach->memory, 0xC000), 123 | 0x80);
+    apple2_clear_strobe(mach);
+    cr_assert_eq(vm_segment_get(mach->memory, 0xC000), 123);
+}
+
+Test(apple2, release_key)
+{
+    apple2_press_key(mach, 123);
+    cr_assert_eq(vm_segment_get(mach->memory, 0xC010), 0x80);
+    apple2_release_key(mach);
+    cr_assert_eq(vm_segment_get(mach->memory, 0xC010), 0);
+}