new cpu throttling routine

src/timing.c

@@ -0,0 +1,102 @@
+/* 
+ * Apple // emulator for Linux
+ *
+ * CPU Timing Support.
+ *
+ * Mostly this adds support for specifically throttling the emulator speed to
+ * match a 1.02MHz Apple //e.
+ *
+ * Added 2013 by Aaron Culliney
+ * 
+ */
+
+#include "timing.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <time.h>
+
+#define DEFAULT_SLEEP 60
+
+static unsigned int sleep_hz             = DEFAULT_SLEEP;               // sleep intervals per sec
+static unsigned long cpu_target_hz       = APPLE2_HZ;                   // target clock speed
+static unsigned long cycles_interval     = APPLE2_HZ / DEFAULT_SLEEP;   // Number of 65c02 instructions to be executed at sleep_hz
+static unsigned long processing_interval = NANOSECONDS / DEFAULT_SLEEP; // Number of nanoseconds in sleep_hz intervals
+
+static struct timespec deltat, t0, ti, tj;
+static unsigned long cycle=0;
+static long sleep_adjust=0;
+static long sleep_adjust_inc=0;
+
+// -----------------------------------------------------------------------------
+
+// assuming end > start, returns end - start
+static inline struct timespec timespec_diff (struct timespec start, struct timespec end) {
+    struct timespec t;
+
+    // assuming time_t is signed ...
+    if (end.tv_nsec < start.tv_nsec) {
+        t.tv_sec  = end.tv_sec - start.tv_sec - 1;
+        t.tv_nsec = NANOSECONDS + end.tv_nsec - start.tv_nsec;
+    } else {
+        t.tv_sec  = end.tv_sec  - start.tv_sec;
+        t.tv_nsec = end.tv_nsec - start.tv_nsec;
+    }
+
+    return t;
+}
+
+static inline long timespec_nsecs (struct timespec t) {
+    return t.tv_sec*NANOSECONDS + t.tv_nsec;
+}
+
+void timing_initialize () {
+    clock_gettime(CLOCK_MONOTONIC, &t0);
+    ti=t0;
+}
+
+void timing_set_cpu_target_hz (unsigned long hz) {
+    cpu_target_hz = hz;
+}
+
+void timing_set_sleep_hz (unsigned int hz) {
+    sleep_hz = hz;
+}
+
+/*
+ * Throttles the 65c02 CPU down to a target frequency of X.
+ * Currently set to target the Apple //e @ 1.02MHz
+ */
+void timing_throttle () {
+    ++cycle;
+
+    if ((cycle%cycles_interval) == 0) {
+        clock_gettime(CLOCK_MONOTONIC, &tj);
+        deltat = timespec_diff(ti, tj);
+        ti=tj;
+        if (deltat.tv_sec != 0) {
+            // severely lagging ...
+        } else {
+            deltat.tv_nsec = processing_interval - deltat.tv_nsec + sleep_adjust_inc;
+            nanosleep(&deltat, NULL); // NOTE: spec says will return right away if deltat.tv_nsec value < 0 ...
+            ti.tv_nsec += deltat.tv_nsec;
+        }
+
+        if ((cycle%cpu_target_hz) == 0) {
+            clock_gettime(CLOCK_MONOTONIC, &tj);
+
+            deltat = timespec_diff(t0, tj);
+            struct timespec t = (struct timespec){.tv_sec=1, .tv_nsec=0};
+
+            long adj = (deltat.tv_sec == 0)
+                ?      timespec_nsecs(timespec_diff(deltat, t))
+                : -1 * timespec_nsecs(timespec_diff(t, deltat));
+
+            sleep_adjust += adj;
+            sleep_adjust_inc = sleep_adjust/sleep_hz;
+
+            t0=tj;
+            ti=t0;
+        }
+    }
+}

src/timing.h

@@ -0,0 +1,27 @@
+/* 
+ * Apple // emulator for Linux
+ *
+ * CPU Timing Support.
+ *
+ * Mostly this adds support for specifically throttling the emulator speed to
+ * match a 1.02MHz Apple //e.
+ *
+ * Added 2013 by Aaron Culliney
+ * 
+ */
+
+#ifndef _TIMING_H_
+#define _TIMING_H_
+
+#define APPLE2_HZ      1020000
+#define NANOSECONDS 1000000000
+
+void timing_set_cpu_target_hz (unsigned long hz);
+
+void timing_set_sleep_hz (unsigned int hz);
+
+void timing_initialize ();
+
+void timing_throttle ();
+
+#endif // whole file