PC speaker support

adlib.c

@@ -1,5 +1,6 @@
 #include "adlib.h"
 
+int adlib_present;
 static void adlib_wait(int delay) {
   int i;
   for (i = 0; i < delay; i ++) adlib_read();
@@ -20,7 +21,22 @@ void adlib_reset() {
   }
 }
 
-void adlib_init() {
-  adlib_reset();
-  atexit(adlib_reset);
+void adlib_detect() {
+  int status1, status2;
+  adlib_write(4, 0x60);
+  adlib_write(4, 0x80);
+  status1 = adlib_read();
+  adlib_write(2, 0xff);
+  adlib_write(4, 0x21);
+  adlib_wait(160);
+  status2 = adlib_read();
+  adlib_present = (status1 & 0xe0) == 0 && (status2 & 0xe0) == 0xc0;
+}
+
+void adlib_init() {
+  adlib_detect();
+  if (adlib_present) {
+    adlib_reset();
+    atexit(adlib_reset);
+  }
 }

adlib.h

@@ -1,5 +1,6 @@
 #include <dos.h>
 
+extern int adlib_present;
 void adlib_init();
 #define adlib_read() inp(0x388)
 void adlib_write(int reg, int val);

fakelib.c

@@ -0,0 +1,51 @@
+#include "fakelib.h"
+#include "timer.h"
+
+void fakelib_shutup() {
+  outportb(0x61, inportb(0x61) & 0xfc);
+}
+
+void fakelib_init() {
+  atexit(fakelib_shutup);
+}
+
+static unsigned int remaining_ticks;
+static unsigned int last_tick;
+static unsigned int fnumlow;
+void fakelib_write(int reg, int val) {
+  if (reg == 0xa0) { // writing a new frequency to voice 0
+    fnumlow = (val & 0xff);
+  } else if (reg == 0xb0) {
+    if (val & 0x20) {
+      unsigned long fnum = ((val & 0x03) << 8) | fnumlow;
+      unsigned int oct = (val & 0x1c) >> 2;
+      unsigned long div = (24L << (20 - oct)) / fnum;
+      unsigned char tmp;
+
+      outportb(0x43, 0xb6);
+      outportb(0x42, div & 0xff);
+      outportb(0x42, (div >> 8) & 0xff);
+      outportb(0x61, inportb(0x61) | 0x03);
+
+      // todo: guess at duration based on instrument decay
+      remaining_ticks = 2;
+      last_tick = timer_counter;
+    } else {
+      fakelib_shutup();
+      remaining_ticks = 0;
+    }
+  }
+}
+
+void fakelib_tick() {
+  if (remaining_ticks > 0) {
+    unsigned int tickdiff = timer_counter - last_tick;
+    if (tickdiff >= remaining_ticks) {
+      fakelib_shutup();
+      remaining_ticks = 0;
+    } else {
+      remaining_ticks -= tickdiff;
+    }
+  }
+  last_tick = timer_counter;
+}

fakelib.h

@@ -0,0 +1,3 @@
+void fakelib_init();
+void fakelib_write(int reg, int val);
+void fakelib_tick();

testbed.c

@@ -18,6 +18,7 @@
 #include "jorth.h"
 #include "egamap.h"
 #include "adlib.h"
+#include "fakelib.h"
 
 /*** T E X T ***/
 char far *font = NULL;
@@ -270,6 +271,8 @@ void game_init() {
   timer_init(TIMER_30HZ);
   text_init();
   adlib_init();
+  fakelib_init();
+  timer_setcallback(fakelib_tick);
 
   loadscr("title");
 /*  f = fopen("TITLE.TIF", "rb");
@@ -407,11 +410,20 @@ void f_drawportrait() {
   DROP(1);
 }
 
+int use_adlib;
 void f_adlib() {
-  adlib_write(TOP().u, ST1().u);
+  if (use_adlib) {
+    adlib_write(TOP().u, ST1().u);
+  } else {
+    fakelib_write(TOP().u, ST1().u);
+  }
   DROP(2);
 }
 
+void f_adlib_present() {
+  PUSHI(adlib_present);
+}
+
 cell f_atexit;
 void f_cleanup() {
   f_execcp(f_atexit);
@@ -827,6 +839,9 @@ void game_f_init(char *exe, char *bootjor) {
   CDEF("boss", f_showboss);
   CDEF("system", f_system);
   CDEF("adlib!", f_adlib);
+  CDEF("adlib?", f_adlib_present);
+  PCONST("use-adlib", &use_adlib);
+  use_adlib = adlib_present;
 
   CDEF("mouseshow", f_mouseshow);
   CDEF("mousehide", f_mousehide);