Add missing file.

arch/c64/c64.cc

@@ -0,0 +1,38 @@
+#include "globals.h"
+#include "c64.h"
+
+/*
+    *   Track   Sectors/track   # Sectors   Storage in Bytes   Clock rate
+    *   -----   -------------   ---------   ----------------   ----------
+    *    1-17        21            357           7820             3.25
+    *   18-24        19            133           7170             3.5
+    *   25-30        18            108           6300             3.75
+    *   31-40(*)     17             85           6020             4
+    *                              ---
+    *                              683 (for a 35 track image)
+    * 
+    * The clock rate is normalised for a 200ms drive.
+    */
+unsigned sectorsForC64Track(unsigned track)
+{
+    if (track < 17)
+        return 21;
+    if (track < 24)
+        return 19;
+    if (track < 30)
+        return 18;
+    return 17;
+}
+
+nanoseconds_t clockPeriodForC64Track(unsigned track)
+{
+    constexpr double BYTE_SIZE = 8.0;
+
+    if (track < 17)
+        return 26.0 / BYTE_SIZE;
+    if (track < 24)
+        return 28.0 / BYTE_SIZE;
+    if (track < 30)
+        return 30.0 / BYTE_SIZE;
+    return 32.0 / BYTE_SIZE;
+}